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ODMP Monitoring Recommendations

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Government of Kingdom of Denmark
Ministry of Foreign Affairs Danida Ref No: 104.Botswana.1.MFS.8

Government of Republic of Botswana
National Conservation and Strategy Agency Department of Water Affairs (DWA) Harry Oppenheimer Okavango Research Centre

Okavango Delta Management Plan
Hydrology and Water Resources

Recommendations for Improved Hydrologic Monitoring
May 2004
Scanagri Denmark A/S
DHI Water and Environment Hedeselskabet CSIR Liebenberg and Stander Engineering Hydrological and Environmental Services

Okavango Delta Management Plan

Hydrology and Water Resources

Table of Contents
1 2 3
3.1 3.2

Introduction............................................................................................................1 DWA Monitoring Programme and Context for ODMP.....................................2 Important Features in Monitoring Design...........................................................3
Hydrological and biophysical processes......................................................................... 3 Experience and lessons learnt from previous monitoring attempts ................................ 6

4 5 6
6.1

Monitoring Programme Objectives......................................................................8 Overview of Existing Monitoring Network .........................................................9 Assessment of Surface Hydrology Monitoring ..................................................10
Network status .............................................................................................................. 10 6.1.1 Water level measurements...................................................................................... 12 6.1.2 Discharge measurements ........................................................................................ 13 6.2 6.3 Dataflow, databases and data availability..................................................................... 13 Proposal for upgrading and rehabilitation .................................................................... 14

7
7.1 7.2

Assessment of Sediment Transport Monitoring................................................21
Existing monitoring ...................................................................................................... 21 Proposal for sediment transport monitoring ................................................................. 21 7.2.1 One year initial study at Mohembo ........................................................................ 21 7.2.2 Horizontal distribution and assessment of riverbed material.................................. 22

8
8.1 8.2 8.3

Assessment of Groundwater Hydrology and Water Quality Monitoring ......23
Monitoring network status............................................................................................ 23 Dataflow, databases and data availability..................................................................... 24 Proposal for groundwater monitoring........................................................................... 25 8.3.1 Delta peripheral monitoring holes .......................................................................... 25 8.3.2 Delta monitoring holes ........................................................................................... 27 8.3.3 Sedimentology ........................................................................................................ 29 8.3.4 Discussion............................................................................................................... 29 8.3.5 Costing for drills..................................................................................................... 30 8.4 Implementation ............................................................................................................. 30

9
9.1 9.2 9.3

Assessment of Water Quality Monitoring .........................................................32
Existing monitoring and assessments ........................................................................... 32 Need for Water Quality Monitoring ............................................................................. 33 Proposal for Water Quality Monitoring........................................................................ 34

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10

Assessment of Hydroclimatic Monitoring..........................................................38
10.1 Network status ............................................................................................................. 38 10.2 Proposal for upgrading and rehabilitation.................................................................... 38

11 12 13

Remote Sensing supporting Hydrologic Monitoring ........................................40 Cost Estimate........................................................................................................41 Implementation Strategy .....................................................................................43
13.1 Formation of task force................................................................................................ 43 13.2 Specification, final site selection and equipment procurement.................................... 44 13.3 Installation, operation and training .............................................................................. 45 13.4 Data dissemination....................................................................................................... 46 13.5 Timing and work schedule........................................................................................... 46

14 15

Summary and Recommendations.......................................................................48 References .............................................................................................................54

Appendix
1 Discharge at Mohembo and Boro Junction and Precipitation. 2 Water level observations at selected stations. 3 Existing discharge measurement sites. 4 Existing water level measurement sites. 5 Existing precipitation measurement sites. 6 Existing sites where Data Collection Platforms (type STS) are installed. 7 Potential upgrade sites for automatic water level data loggers and precipitation gauges. 8 Surface water stations, tentative list. 9 Recommendations to upgrade the surface water monitoring network 10 Proposal and cost estimate for a monitoring/piezometer drilling programme using EUREKA porta-rig 11 Planned methodology for groundwater recharge monitoring (Piezometry)

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1 Introduction
This working paper contains a review of existing monitoring within hydrology and reommendations on improving the data collection and data management of hydrology and water quality in the Okavango Delta in the context of the Okavango Delta Management Plan (ODMP). The review and recommendations are made as part of the DANIDA supported assistance to the Department of Water Affairs (DWA) under the umbrella of the ODMP. The paper was prepared in September/October 2003 and a first draft distributed to the Hydrology and Water Resources Technical Committee under the ODMP in November 2003. The Committee met on 30th January 2004 to discuss the findings and the further approach to embarking on the implementation phase. Reflections on the comprehensive process and valuable information were received enabling a refinement of the recommendations for final approval in May 2004. This working paper is prepared by Steen Øgaard Dahl and Ole Smith both members of the project team (Hedeselskabet – DDH Consulting) based on information and support from the DWA staff in Gaborone and Maun. Background information on groundwater has been gathered by national consultants Israel Mabua and Margaret Joan MacFarlane, who have also assisted in drafting the conceptual approach in improved groundwater monitoring (included in Chapter 8 and Appendicws 10 and 11). The national consultant Francis Sefe has compiled and evaluated the hydrology data, and participated in discussions on surface water monitoring.

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Hydrology and Water Resources

2 DWA Monitoring Programme and Context for ODMP
Water is the lifeline to the Okavango Delta. Data on hydrologic and climatic parameters are essential to assess the functionality and long term trends in the delta and the wise use of the wetland and surrounding area, all part of the 65,000 km2 Ramsar site. As the responsible agency for national water resources planning and development, the Department of Water Affairs (DWA) has an important obligation to provide reliable, comprehensive and systematic information of the hydrology essential for the Okavango Delta Management Plan (ODMP). The review of the existing monitoring programme and proposals for upgrading the programme within the DWA shall be seen in this context. The monitoring programme can also contribute to the OKACOM investigations (Permanent Okavango River Basin Water Commission) to accommodate the legitimate water needs in the entire catchment in a sustainable manner. The review of the monitoring programme has focused on ways to establish long term data series of relevant parameters and further improve the existing monitoring carried out by DWA.

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3 Important Features in Monitoring Design
Consideration and design of any monitoring programme shall take its offset in the function and key processes in the hydrologic dynamics and the interference to the ecosystem (time wise and spatial variation) with due consideration of the likely human impacts. It is not the intention to make a comprehensive overview of the perception of the delta functions from the numerous authors and researchers who have studied the complex interactions in the delta but a few key features have to be kept in mind in the monitoring design. These are summarised in this section of the report.

3.1

Hydrological and biophysical processes

The catchment area of the Okavango River is part of the Makgadikgadi Basin. The basin can be subdivided into several sub-catchments and depression pans that seldom have direct hydraulic contact with one and another (Turton, 2003). The Boteti river catchment directs occasional outflows (seldom and irregular in recent times) of the delta to the Makgadikgadi Pans. The Magwagqana spillway may during very high floods conduct water towards the KwandoLinyanti and Chobe river system, which forms part of the Zambezi River. Thus at times the Okavango River is interlinked with the Zambezi River basin. A sketch of the delta area and temporary outflow pathways are depicted in figure 3.1 and key data on the catchment areas are summarised in Table 3.1. Catchment area Okavango River catchment area upstream of the Delta Okavango Delta (the Ramsar Core area) Boteti River sub-catchment south of the delta Deception, Ntwetwe and Sowa Pan (catchment area south of the delta area proper) Total catchment area of the Makgadikgadi basin Size 413,550 km2 15,844 km2 10,920 km2 284,979 km2 725,293 km2

Table 3.1 - Major river systems in the Makgadikgadi basin and catchment areas (data from Turton, 2003)

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Figure 3.1 – Sketch of the delta area and surrounding pans (from Murray, 1997) The Okavango Delta demarcated as a Ramsar site comprises 65,000 km2 in total, including the 15,844 km2 core area of the delta proper. The peripheral areas of terrestrial ecosystem are thus some four times larger than the wetland site itself. The Okavango River enters Botswana as a single broad river approximately 200 m wide and with depths of around 4 to 5 metres. The river meanders through the floodplain of the Panhandle before it branches into the alluvial fan of the delta. The delta consists of permanent swamps sustained by the base flow from the Okavango River, semi-permanent channels and seasonal swamps relying on the annual flood from the Okavango River and intermittently flooded areas inundated to various degrees during periods of high rainfall in the region. Ecological zones and habitats can be recognised in the delta. In the delta numerous lagoons and oxbows are found and more that 150,000 islands that vary in size from a few metres to kilometres. The sub-stratum of the delta comprises thick layers of sand deposits interspersed with silt layers. The inflow to the delta from the Okavango River is on average approximately 10,000 Mm3 per annum, while direct rainfall to the delta accounts for approximately one quarter of the water budget. Evapotranspiration is the determining factor for the loss of water from the delta although the exact amount is debatable as well as the recharge of the groundwater, making these crucial parameters two uncertain terms in the water balance equation.
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The annual variation in water flow upstream of the delta (Mohembo in the Panhandle) and the southern part of the delta (eg at Boro Junction upstream of the confluence with the Thamalakane River) is illustrated in figure (3.2). The inflow variation at Mohembo (the hydrograph) is fairly gentle over the year. Flooding of the delta slowly propagates southward and the peak reaches the distal part at Maun some 3 to 4 months later - if the inflow and rainfall has been sufficient.
800

700

600

500 Q [m3/s]

400

300

200

100

0 1978 1979 71.12 Mohembo, discharge 1980 1981 74.12 Boro Junction, discharge 1982

Figure 3.2 – Variations in flow at Mohembo and Boro Junction in the period November 1977 to January 1982 (example). The water level variation in the Panhandle is up to 2 m but the variation in water level in the permanent swamps is not very distinct and in parts of the delta is as low as 10 to 15 cm over the year. This is due to the water spreading out over a large area in the alluvial fan (Figure 3.3).

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3.00 2.75 2.50 2.25 2.00 1.75 H [m] 1.50 1.25 1.00 0.75 0.50 0.25 0.00 May 1992 Jul Sep Nov Jan 1992 1992 1992 1993 71.12 Mohembo, waterlevel 72.15 G aenga, water level Mar 1993 May 1993 Jul 1993 Sep Nov Jan Mar 1993 1993 1994 1994 74.12 Boro junction, waterlevel May 1994 Jul 1994

Figure 3.3 – Water level variation at Mohembo, Boro Junction and Gaenga, in the period April 1992 to July 1994. Y-scale is 3 meter. Variations at 2.8 m at Mohembo, 1.2 m at Boro and only 0.1 m at the Eastern delta station Gaenga (example). The sediment transport into the delta in combination with dense vegetation in the inundated floodplain, temporary blockages in channels due to build up of weeds, new tracks made by hippopotami, peat fires in blocked and inactive channels, etc make the flow pattern dynamic and ever changing. Tectonic disturbances altering the weak gradients are believed to add to the dynamics of the water distribution in between the eastern and western channels. In general, the flowing waters in the delta are fresh (low in salts) but in stagnant water pools, peat and soil matrices in islands, salt accumulates through the processes of evaporation and transpiration from the vegetation. The role of vegetation is a central and complex mechanism in preventing the delta becoming a saltpan. Some of the mechanisms are illustrated in Figure 3.4 and Figure 3.5. The monitoring programme of the hydrologic features has thus to take account of the pronounced heterogeneity of the area (patchiness). The extreme variations and dynamics in the processes are in no way fully understood. The monitoring programme of DWA is aimed at keeping the broad hydrologic functions under observation and not entering into a detailed assessment of process dynamics which are beyond a systematic and routine monitoring approach.

3.2

Experience and lessons learnt from previous monitoring attempts

Considerable effort has over time been expended on monitoring programmes on hydrologic parameters and for years intensive monitoring of surface waters has been carried out. The lesson learnt from previous and present monitoring is that logistic difficulties are significant and shall be taken into account in the setup of additional monitoring. Transport in the delta area with vehicles (4x4) or by boat is time consuming and for periods even impossible.

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Figure 3.4 - Diagram illustrating some processes in the permanent swamp vegetation (from Murray)

Figure 3.5 - Schematic floodplain-island groundwater interaction in the Okavango Delta explained by McCarthy & Ellery, 1994

Manual measurements at the field stations in the delta face risks from wildlife. Remotely operated data collection platforms (DCP) are constantly subject to the threat of damage from wildlife and theft of vital parts. Fieldwork has to face drawbacks and it will be too optimistic to expect a smooth operation of the fieldwork even with thoughtful planning. However there is room for improvements in procedures. The lack of skilled staff in maintenance of advanced equipment, lack of staff to run the laboratories, data processing and interpretation is another constraint that has to be balanced with the vision of establishing a comprehensive monitoring programme.

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4 Monitoring Programme Objectives
The overall objectives and the principles for the monitoring programme for the Okavango Delta are reflected in the objectives and principles stated below. The objectives have guided the review and recommendations: 1. The monitoring programme shall add to sound and reliable hydrologic data to be provided by DWA and to be used for the integrated hydrologic model within and beyond the project period, and for other stakeholders active in the management of the delta 2. The monitoring programme shall make possible documenting long term trends in the hydrology, sediment transport and basic water quality parameters caused by natural dynamics as well as man induced impacts 3. The monitoring programme shall focus on the most likely pressures and future impacts from upstream the delta and changes within the delta with respect to - changes in land use upstream (agriculture, erosion, sediment transport and catchment changes) - increased water abstraction for irrigation and water demand upstream in Angola and Namibia including dam construction and alterations in sediment transport to the delta - increased water abstraction from the delta area (fringe area) itself - concerns of climate changes - concerns of in-stream flow requirements (environmental water requirements) ie what is required in terms of water inflow to the delta in order to sustain the delta function - water pollution from activities upstream of the delta and likely impact within the delta 4. The monitoring programme shall be within the scope of DWA’s activities and be carried out as a systematic and ongoing programme 5. The programme shall be a balance between the cost and the usefulness of the data for the future 6. The monitoring shall not have the character of research – that is left for other institutions to carry out.

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Okavango Delta Management Plan

Hydrology and Water Resources

5 Overview of Existing Monitoring Network
The coverage of surface water measurement stations in the delta is dense. More than 60 water level sites with gauge boards have over the years been established in the delta and some 9 stations are (or have been) equipped with mechanical paper chart recorders. Discharge is measured at nearly 30 sites with a varying frequency. A total of 8 remotely operated Data Collection Platforms (DCP) is installed in the delta in 1995, but unfortunately hardly any reliable data have been gathered. The majority of the stations is presently out of function. The DCP stations are equipped with water level recorders and raingauges. Furthermore 2 DCPs in the delta have several extra sensors for hydroclimatic measurements. In Mohembo an extra DCP is installed (SADC-Hycos) and this station is measuring several water parameters and hydroclimatic parameters. Data are available from the internet. Precipitation is also measured by the Department of Meteorological Services (DMS) at Mohembo, Maun, Shakawe, Gumare, Nokaneng and Sehitwa, all in the fringe area of the delta. Regular groundwater monitoring is mainly confined to wellfields in the southern part of the delta around Maun. An overview of the stations and parameters can be found in Appendices 3 to 6. Owing to a number of discrepancies between various data sources having different spelling of geographical names, misunderstanding of ID numbers, etc there are some inconsistencies and missing locations in the overview. These are highlighted and the DWA Modelling Unit is in the process of rectifying the names, correct locations and ground truthing the existing locations with geographical coordinates.

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6 Assessment of Surface Hydrology Monitoring
This chapter comprises an overview of the present status of water level and discharge measurements in the delta and an outline for improved surface hydrology is proposed. Basically, monitoring of surface water hydrology comprises water level (stage) readings, discharge (flow) measurements and parameters used for calculating the discharge (cross section and water velocity) and all stages of data gathering from fieldwork, data entry, data handling, storage, interpretation and derived values, etc. A dense network of surface hydrology stations enables a description of regional water level variations both of long term trends and within the season (short term), and also the discharge distribution in a lengthwise and crosswise direction of the delta. Furthermore, information on river cross sections is of importance when river routing has to be modelled. Finally overall water balances on inflow and outflow require systematic flow measurements. The Okavango Delta has been subject to intensive water level and discharge monitoring during the past decades. Gauge boards totalling at least 60 locations are fairly well distributed throughout the delta although long and systematic time series of water level readings are far less than the number of gauge plates. Likewise discharge measurements have been made periodically throughout the delta totalling at least 30 locations. Discharge measurements also suffer from gaps in monitoring and a large number of the discharge stations has only few annual readings. For the time being less than 10 stations have long time series with a dense number of annual readings also covering the recent years. Of utmost importance to the interpretation of discharge measurements and flows in the river system and channels in the Okavango Delta is the fact that hardly any locations in the delta have a well confined river cross section containing the full flow. Part of the discharge in a river valley cross section will trickle through the floodplains comprising vast areas of reed, papyrus and other aquatic vegetation. The proportion of bypass discharge depends on the actual water level (flood versus dry season) and thus hampers interpretations. Examples of variations in flow and water level are presented in Appendices 1 and 21. The variation is depicted for three stations in the delta (discharge on the left axis and water level on the right axis). The upper plot includes data from Station 7215 Gaenga in River Ngoqa, Station 7445 Xakue in Boro River and station 7565 Txaba (or Dxaba) at the Santantadibe River. It is obvious that the Boro River has the largest annual variation in both discharge and water level while the two stations in the north eastern and eastern part have minor variations only.

6.1

Network status

Knowledge of the hydraulic function of the delta is crucial in designing the monitoring network. The major river in the delta is the Boro River system, also named Jao River in the upstream part. The Boro River consists of a variety of channels dividing and converging on its way to the Thamalakane River, which routes the water through Maun. Before the confluence, some flow is diverted to the Xudum system, which routes water to a confluence upstream lake Ngami, south west of Maun.

Note: The data and the times series have not been subject to exhaustive data check and validation – this is ongoing Recommendations for Improved Hydrologic Monitoring

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Downstream of the Panhandle waters from the Okavango River are routed to the west to the Thaoge River system that has gradually become blocked over the last decades although water still trickles through the river system. The other major river system is the Ngoqa river flowing to the east of the Boro. The Nqoga river system is further east divided into the Maunachira–Khwai and Mboroga. The latter is diverted into in the Santantadibe and Gomoti Rivers.

#

Muhembo

#

Sepupa
#

rivers towns roads swamp

Gumare

Nokaneng
#

Maun

Tha

N W S E

Tsau
#

oge

Th am

al ak an e
# #

Figure 6.1 - The river systems in the Okavango Delta. The network of water level stations, discharge stations, precipitation and DCPs (Data Collection Platforms) is illustrated in Appendices 3 to 6. Appendix 8 shows the stylised river system, the measurement station, number and name, coordinates and the gauge zero, and which parameters are measured and type of measurement system. The table is an outline of the information gathered in October 2003 and updated in May 2004. Comparing various data sources in DWA there are discrepancies in names and numbers. The Hydrological Model Unit is in the process of making the data identification homogeneous.

Recommendations for Improved Hydrologic Monitoring

Okava
Etsha 6
#
#

ngo
Seronga
#

N qo ga
chira Mauna Ja o

Kh wa i
G om ot i

ro Bo
Shorobe
#

Toteng
#

e yer Kun

Matlapaneng

Makalamabedi

Bo te ti
#

Sehithwa
#

0

40

80 Kilometers

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Okavango Delta Management Plan

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6.1.1 Water level measurements In the Okavango Delta there are located over the years at least 60 water level observation stations. These are either equipped with automatic recorders (8 DCP and 9 chart recorders) or they are manual gauge board readings. A few of the gauge board readings are daily and some are periodic. A fairly high number is not read anymore because of damage, the river section has been inaccessible due to vegetation blockages or has been dry for years. The annual water level variation in the delta ranges from only 10 cm at certain stations in the middle of the delta to several metres both in the Panhandle and at the outlet eg at Boro Junction. The automatic chart recorders are either of the type OTT (German manufacture) with a reputation for reliability, or they are chart recorders from the US mark Stevenson. Both types use the flotation principle to measure water level and data is recorded on paper charts. The recorders are in general old and spare parts are often absent when the local field staff have to repair and maintain the equipment. Illustrative examples from gauge boards and automatic water level recorders are seen in Figure 6.2.

Figure 6.2 – Automatic water level recorder (left) at station 7425 - Kwihum, (Jao-Boro River) and gauge board 7154 - Duba on the Nqoga River. Both stations are located in the permanent swamp area. In 1995 eight DCP measurement stations of the type STS (from Space Technology Systems in UK) were erected in the delta (and a further 12 stations elsewhere in Botswana). Six of the eight DCPs were equipped with water level and precipitation sensors only. The last two stations were extended with other climatic parameters namely air temperature, relative humidity, soil temperature, solar radiation, wind speed, wind direction, conductivity, and turbidity. The data are transferred to DMS by satellite and only distributed to DWA if requested. Water level is measured based upon the pressure transducer principle where cables have been wired from the station to the riverbank through PVC pipes. The transducers are located in the riverbank. The transducers compensate the influence of the atmospheric pressure through small air tubing in the cable. The systems can be very sensitive and precautions have to be made when operating the transducers. Despite securing the stations with electric fences several stations have been out of function due to vandalism and some of the cables to the water level sensors have been dug up the ground by animals. So far no usable data has been retrieved from the stations due to vandalism shortly after installation or due to the fact that nobody has requested the data collected by DMS.

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Figure 6.3 - The DCP station (left) at Moumo, Boro River in October 2003. The station was in function until 2002 where the solar panel was stolen. The remaining equipment seems to be in good order. The DCP station (right) at Xugana, Maunachira River in August 2003

6.1.2 Discharge measurements Discharge measurements are carried out with current meter instruments procured from OTT. The OTT instruments are reputed as reliable and robust. The measurement standard used is the 2-point method (0.2 and 0.8 of the depth). Mean velocity is calculated in the vertical and the midsection method used to calculate the discharge. At Mohembo the distance between the verticals is 5 metres as standard and consequently around 20 verticals are measured. The 2-point method is one off the international standard methods commonly used. To improve the discharge, additional points in the verticals could be introduced and another calculation algorithm used but the impact is increased measurement time and more complex calculations. A computer programme might be necessary. In the delta, around 30 discharge stations are distributed. At the Mohembo station the discharge measurements are carried out on a daily basis. Other stations are measured at monthly intervals or more intensively in periods with floods. A complete overview of the time series is in the process of being made available and cross checked as part of the hydraulic modelling. The regional office at Gumare is measuring the sites in the Panhandle and the upper and Western part of the delta while the Maun office is in charge of the Southern, Middle and Eastern part of the Delta. According to information obtained in 2003 at least three current meters are available for the staff in Maun whereas one is positioned in Gumare.

6.2

Dataflow, databases and data availability

All monitoring is managed by the local DWA offices in Maun and Gumare. The field personal read the water level and keep the gauge boards levelled to local benchmarks positioned nearby on solid ground. They also maintain the mechanical water level recorders, change the chart, wind the clock, etc. The manual water level readings are entered on standard forms. The final results are forwarded to the DWA head office in Gaborone. The data from the forms are entered into the HYDATA database system. Original forms containing raw data are kept in the local DWA office.

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The discharge measurements are noted on specific discharge forms in the field, with information of the instrument number, start time, end time, water level, distance from the bank, depth in verticals, depth of measurement point, time of measuring, and rotations. When the measurement is finished the discharge is calculated at the local office or immediately in the field. No standard calculation programme is used for this operation and the calculation is made with a pocket calculator. The final results of discharge, the mean velocity, the cross section area and water level are forwarded to DWA in Gaborone but all other information is only kept in the paper forms. The charts from the mechanical chart recorders are brought to the local office where daily readings are converted into a second form. These forms are mailed to Gaborone where an operator manually keys these figures into the HYDATA database for storage.

6.3

Proposal for upgrading and rehabilitation

Based on the assessment of the water levelling, discharge measurements and area distribution of the stations a set of recommendations is made divided into network coverage, equipment, measurements and dataflow. Tentative recommendations on the future monitoring network are detailed in Appendix 9 and summarised below. Network In broad terms the existing network of water level and discharge stations is sufficient to cover the delta dynamics in a reasonable way although a few additional stations at key points could be desirable, such as those proposed by Dr Naidu. A crucial point in improving the monitoring programme is to determine the frequency and density of gauge readings and discharge measurements carried out by the field staff. At present most of the DWA stations listed in Appendix 8 are in operation - at least in principle, but data are not available at all stations. Lack of data on certain stations is either due to long dry periods of the river section or blockage of the river system making access to the gauge board impossible or other reasons. Based on a tentative analysis by Francis Sefe (EHAS, 2003) on available readings entered into the DWA database, the stations with reasonable data coverage within the last 5 years can be condensed to


7 stations with discharge measurements taken frequently (almost daily) and around 14 stations with scattered frequency (or seasonally) 13 stations with water level readings are taken frequently



In additional to the existing water level stations presented in Appendix 8 it is proposed to establish one additional station at Xudum River near the Buffalo Fence. The existing network of discharge stations and the frequency of measurement will be refined based on results from the hydrologic model. Measurement equipment, water level Firstly it is recommended to make an initial check of the few existing mechanical recorders to check the status and function. This was not possible during the mission but according to information received it appears that in general the recorders are not functioning well. It might therefore be reasonable to build up a new system of automatic water level recorders. The recorders shall in some areas be able to record an annual water level variation as low as 0.1 metre and in other areas a variation of several metres.
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The recorders shall be capable of storing data for at least one year, recording every hour, and there shall be an easy data collection facility not sensitive to adverse and harsh weather conditions. One option would be to use a data logger type measuring the water level by the capacitive principle. These data loggers are either a 1 metre or 2 metre unit in non-corrosive steel pipes. In the top of the pipe, the data logger is located and a small lithium battery lasting for around 5 years of operation powers it. These data loggers could be installed inside a normal steel pipe secured to the gauge board. The field staff operating this system shall change the loggers monthly by reconnecting the existing logger, fill in the necessarily forms and make sure that the logger is marked with the ID of the actual station. In this way all data loggers can be replaced in a scheduled operation and data can be uploaded to a computer at the Maun office. The data loggers are easy to install, not very visible and tempting to vandalism and not expensive compared to other water level systems. The only operational limit is that the range is a maximum of 2 metres. A second option could be to continue with the robust floating system. As an example OTT makes an inexpensive logger with changeable 1.5-volt batteries. A display makes it easy to operate. The disadvantage with the system is that the field staff have to bring a computer or a special weather resistant PC notebook to collect the data in the field. Paper recorders are not recommended even though they are well known as a robust recording system. The reason is that all transformation of data has to be done manually or by digitising, which is not available at the local offices. No remote communication is recommended to the water level stations. The more valuable the electronic devices installed, the higher the risk of vandalism. Therefore it is recommended to keep the basis water level measurement as simple as possible, easy to maintain, robust and as invisible as possible. Add on flash memory cards to the stations can be an advantage so that they just have to be replaced at every visit. Tentative recommendations of some of the technical specifications for a water level logger are: • Accuracy – 0.01 metre • Power supply – battery • Low power consumption • Data storage – at least hourly recording for one year • Data transmission – Replaceable Memory Card • Operational temperatures within the possible range in the Okavango Delta area. • Data display and keypad present • Water level adjustment shall be possible without bringing a laptop • The equipment has to be small due to proposed installation inside a stilling well or at a gauge board. • The sensor unit has to be easily replaced with a spare unit. • The sensor unit has to be robust and not sensitive to shock or humidity.

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Finally it is imperative that the water level recording has to be done to datum level and corrected to the same benchmark. All benchmarks in the area have to be tied to a reference datum level. The Department of Surveys and Mapping (DMS) has levelled the majority of the existing gauge boards in 2004 (almost complete by April 2004). The gauge plate zero and the coordinates are included in Appendix 8. As an overall estimate and for budget estimate, a total of 15 automatic water level recorders are recommended. DCP stations Information on DCPs and recommended upgrade is summarised in Table 6.1.
Name Mohembo River Okavango Comments and recommendations The DCP from Space Technology Systems is not in operation. No vandalism is reported but there is no output from the station. The parallel DCP operated by SADC-Hycos transmits data to the office in Pretoria. There is no reporting of data quality. Data can be obtained from the website www.sadchyco.pwv.gov.za and it can be seen that the station is actually in operation (October 2003). A quick review reveals that some parameters seem reliable while others are dubious. DWA should pay special attention to the sensors at this station. Comments: The STS DCP can be removed and equipment in good condition can be used at other locations as spare parts. The SADC-Hycos needs a service visit. Guma Lagoon Thaoge The DCP is of TYPE A. This station has been vandalised twice shortly after installation. First the solar panel was stolen and after replacing this, there was a break-in where the new solar panel was stolen together with the battery and all cables were cut into pieces. Comments: The station has to be moved to a nearby lodge. DWA should inquire of the owner to find out if this can be realised. Kwihum Boro The DCP is of TYPE B: Vandals irreparably damaged the DCP equipment a month after installation. The stilling well at the site has not been vandalised. Comments: This station has to be relocated and new cables, solar panel, batteries and some sensors have to be procured. Gaenga Ngogha The DCP is of TYPE A: This DCP has never been disturbed since it was installed. The only problem at this site is flooding during high flows but this is not affecting the equipment in any way, though it is reported that the field staff get electric shocks from the fence. The raingauge is not in order and is an older version from SIAP Bologna in Italy. The raingauge model is phased out and no spare parts are available. Comments: The site seems suitable and alternative sites are not obvious. As a tentative strategy it is recommended to keep the station where it is and some security precautions taken in floods. A new raingauge has to be procured. The final decision shall be taken based on a site survey.

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Xo-Flats

Boro

The DCP is of TYPE A: This DCP site is one off the most reliable with respect to human disturbance because the site is difficult to access both by boat and vehicle. Elephants or buffaloes have trampled the water level transducer. Comments: This station can be continued but a stilling well and a new water transducer has to be procured.

Dxaba

Santantadibe

The DCP is of TYPE A: The logger unit usually transmits out of its time slot. The site is good. The water level transducer has been destroyed. Comment: Stilling well has to be installed.

Xugana

Maunachira

The DCP is of TYPE B: The DCP is located on the edge of the lagoon. The site is suitable. Comments: Construct a stilling well and make a connection pipe to the river. Make sure that the pipe from the well to the station is well below ground level preventing animals digging it up.

Moumo

Boro

The DCP is of TYPE A: This DCP is located at a suitable site. The solar panel was stolen in 2002. The water level sensor is irreparably damaged by animals. Comments: although the solar panel has been stolen this station seems to be well located. One new solar panel has to be procured. Instead of using ordinary bolts one could either use torx-bolts or weld the panel to the frame. This should be considered as a preventive strategy for all DCPs

Notes: TYPE A – DCP stations comprising two remote sensors: Rainfall and Water Depth (measured with pressure transducer). TYPE B – DCP stations with more than two sensors: Rainfall, water depth, wind velocity, wind direction, combined temperature and humidity, barometric pressure, solar radiation and soil temperature.

Table 6.1 - Overview of DCP stations and actual status as per October 2003 (based on interview with Charles Letsholathebe (DWA) and additional comments concluded from meetings with DWA)

DWA in Gaborone and Maun must have direct access to the data from the DCP stations. The solution with DMS as sole data provider is not durable and shared data access shall be implemented with a dual system between DMS and DWA. DWA has to procure software, field test kit and other devices for the DCP stations securing proper test and data retrieval to DWA office PCs. The DWA's technical person in charge, Charles Letsholathebe, should be able to arrange this set up. DWA needs additional personnel backup for operating the DCPs.

Discharge Measurements. In general well functioning, regularly calibrated current meters have to be available for the field measurements. Related equipment such as rods, winches, counters and other devices are part of the packages. At least one complete set for each field team is necessary, and at least one extra set has to be accessible within reasonable transport time. Essential equipment and inexpensive items such as counters should always be included as spares when the field team is operating.

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For the time being it seems that there is no reason to change the routines of operating the discharge measurements although there are more sophisticated instruments on the market, eg acoustic Doppler profilers for discharge measurements, electronically measurement books, etc. An attempt could be made at Mohembo to improve the discharge measurements. To enable a review the discharge measurements have to be scrutinised for minimum, mean and maximum discharges. One option could be to reduce discharge measurements to every second day. The days in between could be occupied calculating rating curves. The recently installed cableway at Mohembo may facilitate more intensive measurements in additional verticals and still save operation time. In parts of the delta the fluctuation of the hydrographs is rather gentle and therefore it might be acceptable with two discharge measurements per month. In other parts the hydrographs are highly seasonal with low flow or no flow for months where discharge measurements might be meaningless (or impossible) while flood periods will raise the flow and water level rapidly. This will require intensive discharge measurements on the rising limb and around the peak with a frequency of say one to two measurements per week (this is carried out at a limited number of stations). The optimal strategy has to be assessed for the individual stations based on time series to be established as part of the modelling unit. The working document on hydrology data (EHES, November 2003) will serve as a start on this assessment. If rating curves shall be established at least daily water level measurements have to be carried out. It is likely that vegetation in and bypass of adjacent flood plains might influence the hydraulic conditions at many stations. Standard rating curves might not be usable and as an alternative dynamic rating curve calculations have to be introduced if continuous daily records are needed. The assessment will be part of detailing the implementation of the improved monitoring programme. Dataflow It is recommended that the results from the current meter measurements are stored in a database with profile information, velocity values, instruments, calibration functions and other information. This will give an excellent opportunity to monitor both sediment deposition and erosion in the profiles, and it will give a significant quality control opportunity when data are in digital form. There are software programs on the market capable of current meter calculations and data storage and it is recommended to use these and relate it to the HYDATA software and database. All data shall be subject to routine backup functions carried out as daily operational procedures. It is also recommended that all field staff involved in monitoring operations shall be acquainted with the background for the monitoring and a broader understanding of the context of the monitoring and the further interpretation and use in modelling. In this way the best commitment of all persons are secured and eventually increase the data reliability. At the local offices there shall be computer and software facilities so that the staff closely related to the measurements and the locations are able to carry out quality control of incoming data as soon as they arrive at the office. The local offices shall transmit electronic discharge data and water level data to Gaborone within a fixed period (monthly or quarterly). Existing and readily available data from past recordings in the delta have been subject to gathering and systemised review in 2003/2004 as part of the Hydrology component. Various checking procedures and validations have revealed shortcomings and recommendations in
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improved data handling are suggested in the report Hydrology Data (EHES, April 2004). The recommendations are for easy reference for the continued approval procedure and steps forward in the implementation approach summarised in the following text box:

Recommendations on improved data handling quoted from the working paper prepared by Prof Francis Sefe – EHES (November 2003/update April 2004):
• The practice of manual gauging means that data cannot be collected continuously throughout any particular season, unless the site is fitted with an automatic water level recorder. Thus there is always a long gap between the actual gauging. These gaps are filled with “m” in the database indicating missing data, which is strictly not correct. It is recommended that some of the gauging sites be automated so as to provide continuous flow records during the flow season. The selection of such sites should be done in such a way as to achieve adequate spatial representation. Additional recommendations will be made in this regard. The practice of filling the intervening period between gauged flows by linear interpolation and then incorporating the interpolated values into the primary database should be stopped. The primary database should contain the actual field observations only. In regard to the above, DWA should institute a programme of routine processing of the primary data to obtain such secondary or derived data such as rating curves, cross-sections, evaluating outliers and trends, etc. That is the creation of secondary database, as distinct from the primary database. The structure of the information in the database needs to be revised to incorporate the names of the watercourses. It is not adequate to give only the name of the site only. The data entry clerk needs closer supervision of her work. Review the primary database and remove all interpolated and estimated values. A hydrological research exercise should be undertaken to quantify the flow that misses the Mohembo gauging station. This will help in devising a correction factor to be applied at the Mohembo gauging site. This is necessary because it is now too late to move downstream to another site as a permanent cableway has now been constructed at Mohembo. As a matter of urgency, “official” rating curves should be established for all gauging sites in the database. The process should be under the control of one senior officer and amendments effected annually after the flow season has ended. Zeroes or the words “Ceased-to-flow” or “no flow” should be used to indicate a situation whereby although the river had water, there was no flow to measure because the water had become stagnant while the word “Dry” is used to depict a situation of a river drying up completely. Periodic training given to the data gathering personnel in the field would go a long way toward the alleviation of some of the operational difficulties identified. Such training should include instrument handling and storage techniques. Closer supervision of the field staff by senior staff is required. There is a clear morale problem at the outstations. There is the feeling by some of the field-based staff that they have been banished into professional oblivion. This perception is encouraged by the absence of regular visitation from staff at headquarters.

• • • • • •

• • • • •

Re-assessment of the field monitoring programme and remedial action All persons involved in field monitoring and data assessment in the delta recognise the difficulties in carrying out the work and at the same time struggle with logistic constraints and shortages in spare parts for operation and maintenance. With the improved understanding of the hydraulic functions obtained from the thorough data assessment (eg data from the last 5 years) and the hydraulic modelling it is recommended to carry out a general overhaul of the field monitoring logistics and annual planning of the field staff work. The aim is to assess whether there is room for improved efficiency or ease of time consuming field work of little value to the monitoring programme. Furthermore, likely pitfalls in logistics and monitoring routines shall be identified. The review and overhaul shall be made in close collaboration and dialogue with the field staff having hands-on experience in all aspects of the data collection. Based on the overhaul
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remedial actions shall be implemented in parallel with the new equipment installed. In costing the improved monitoring programme a budget line is included for various additional equipment and tools that will ease the logistic constraints and streamline the data reliability and data flow.

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7 Assessment of Sediment Transport Monitoring
Sediment transport in rivers is a natural process but can be significantly altered owing to changes in the runoff regime and land use in upstream catchment areas. Changes in land use and dams in the upstream Okavango Basin are of particular concern. The Okavango River has considerable bed load transport of sand but a remarkable transparency in the river and low levels of suspended solids year round, although pulses of suspended solids are likely in peak flow periods.

7.1

Existing monitoring

There is no systematic long term monitoring of sediment transport in the Okavango Delta. Previously, some research studies have been conducted and they can to some extent highlight the mechanisms in the delta. A monitoring programme in the Okavango Delta has to ensure that both the long term monitoring and the ODMP modelling will have reliable data as input.

7.2

Proposal for sediment transport monitoring

The sediment transport monitoring programme is proposed consisting of two parts: i) A one year intensive assessment at Mohembo supplemented with ii) a one off post flood campaign in 2004 assessing bed material composition (grain size) at around 20 discharge stations distributed in the delta. Based on the experience from the one year study the long term programme shall be determined. 7.2.1 One year initial study at Mohembo It is recommended to launch a monitoring programme on sediment transport (bedload and suspended solids) at the gauging station at Mohembo to obtain basic data. The monitoring programme shall enable assessment of the seasonal variation of the sediment transport as well as estimate of the annual amount of sediment transport. As discharge measurements are carried out every day at Mohembo and the station is permanently staffed it will be a moderate task to include bed load and suspended solids sampling once a month in the dry season and more frequently in the flood period, eg twice a month. The installed cableway will be useful for this purpose otherwise sampling can be done from a boat. Common samplers for suspended sediment in rivers are samplers as DH-76 and DH-74 (Rickly Hydrological Company, www.rickly.com or other companies supplying equivalent equipment) or alternatively water samplers (say 5 litre volume) with flaps operated from the water surface will be adequate for this purpose. Different procedures can be applied for sampling suspended solids. Because intensive current measurements are carried out at Mohembo, the EDI-procedure could be an acceptable approach (Equal Discharge Increment procedure). Through this method the cross section is divided into several segments of equal water discharge. The method is described in WMO (Pub 686). Bed load sampling can be carried out with standard bed load samplers (eg US BL-84). The methods are described in WMO (pub 686). Although it is recognised that bed load transport estimates based on in-situ measurements are highly uncertain the importance of the data and information gathered on a long term basis outweighs the uncertainties.

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The bed load transport sampling should be supplemented with grab sampling of the river bed material at eg 5 to 10 positions in the cross section at Mohembo at regular frequency and analysed for grain size distribution. Analysis of suspended solids and dry weight of the bedload samples is fairly easy and can be carried out in the Maun DWA laboratory. Grain size distribution analysis is routine in geological laboratories. Transport of the samples can be coordinated with the water quality programme (see Chapter 9). As an initial assessment it is proposed to carry out a one year sediment transport study at Mohembo in a collaboration between DWA and HOORC. The option has been discussed at the Technical Committee Meeting in January 2004 (commenting the November version of this report) and Piotr Wolski, HOORC in May 2004 has reconfirmed the interest. The contribution from HOORC would be planning and instructions in the methodology and equipment selection/description, occasional supervision of the field staff, and data interpretation. The DWA contribution would be field sampling carried out by the permanent staff located in Mohembo, transport and analysis of samples (suspended sediment analysis, dry weight, grain size analysis, etc) and manufacture of the bedload sampler at the DWA workshop (or alternative procurement). The water sampler shall be procured (part of the water quality programme – see section 9). Based on a one year sediment transport assessment (full flood period) a long term programme will be decided. It will be assessed whether downstream stations should be included in bedload monitoring in flood periods (eg North Gate, Khwai River and Boro Junction) although it is doubtful the two stations carry significant amounts of bedload transport. 7.2.2 Horizontal distribution and assessment of riverbed material Data on riverbed material composition (sand, loam, clay) and the horizontal distribution in the delta is vital for the hydraulic sediment transport capacity assessments by the hydrologic model (in the second half of 2004). It is recommended to plan and carry out a one off campaign in the 2004 post flood period assessing these aspects. The sampling shall comprise riverbed material (grab or core sampling) from cross sections in the frequently visited discharge stations in the delta (around 20 stations). The sampling is straightforward and can most likely be fitted into the tasks of the field staff carrying out the routine discharge measurements. The grain size distribution analysis shall be carried out in a laboratory having experience in soil analysis. Data interpretation will as part of the hydraulic modelling direct a long term monitoring programme of sediment transport, in conjunction with the one year initial study at Mohembo.

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8 Assessment of Groundwater Hydrology and Water Quality Monitoring
This section focuses on monitoring groundwater levels and groundwater quality in order to assess long term variations in groundwater conditions, both in the groundwater resources not having a direct impact on the local groundwater abstraction as well as from areas of intensive water abstraction in the fringe areas around the delta. Substantial parts of the information on the numerous groundwater boreholes and actual status of the exploration of groundwater resources and various databases have been provided in a working document prepared by Israel Mabua, (Mabua 2003). Understanding the functioning of the delta has to face the problem of the extreme variability of the outflow in relationship to the inflow. Outflow is essential for water supplies along the Thamalakane and in the Maun area in particular, also for the communities living along the Boteti, where the recent dry years have caused severe stress on water availability (GOB 2002). Previous modelling (Dincer et al 1987, SMEC 1990, Scudder et al, IUCN (1993) of the surface outflow, using over twenty years of rainfall, evapotranspiration and stream flow data, showed fluctuations in outflow which could not be explained, either by changes in the flow system within the delta or by data of inadequate quality. Gieske (1997) showed that substantial model improvement is achieved when both long (10 years) and short term (1 year) antecedent climatic conditions are considered. In effect, the delta has a long memory. During periods of poor flooding, the groundwater level goes down progressively (ca 1 m/yr at Beacon Island, without abstraction) and when good flooding returns, the progress of the flood is inhibited by losses to the dry substrate, an empty sponge which must be filled before the progress of the flood and outflow of the delta can express the enhanced inflow. Groundwater data therefore become essential components of successful modelling. Although recognition of this need is not new, the task of achieving it within a realistic budget appears daunting. It is essential for a successful monitoring programme that: • the selection of sites in limited areas must provide data which are representative of the delta as a whole; they must be selected to represent specific terrain units within the delta mosaic • The selection of sites must be made to address key issues, recognised to be relevant to the delta as a whole • Monitoring should use specific techniques appropriate to the issues being addressed; it should be tiered in terms of technology to constrain costs Extrapolation of data from the monitored areas depends on its being firmly anchored to terrain units, identified by studies of satellite images and aerial photos.

8.1

Monitoring network status

Within the area covered by ODMP (essentially the Ramsar border) there exist at least 1074 boreholes according to the National Borehole Archive Database. The majority of the boreholes is in the southern fringe area and west of the delta (west of Thaoge River) while boreholes to the eastern part and northeast of the delta are very few. Boreholes in the delta proper are almost absent (see Figure 8.1).
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# # ## # # # # Muhembo ## # # # # # ## # # # # # ## ## # # # # #

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Figure 8.1 - Boreholes in the area of the Okavango Delta and fringe area

Monitoring of water levels in some of the boreholes has been carried out by DWA since the mid 1980s and time series are stored in the database WELLMON. The monitoring has to distinguish at least three definable groundwater aquifers namely a shallow unconfined aquifer, a leaky semi-confined aquifer and a third underlying aquifer recognised to contain brackish water at depth. Under extended pumping stress regimes these aquifers seem to interact through leakages into one another. The largest numbers of water level monitoring boreholes are installed in well fields surrounding the Maun area (Shashe river valley, Thamalakane, Kunyere, Gomoti and Boro area) and time series can be established from 1985. The monitoring of water levels in this area is a mixture of impact from local abstraction of groundwater resources and overall fluctuations of the groundwater replenishment due to climatic variations. From the various groundwater studies it is deemed possible to gather and present an overview of spatial variation in rest water levels (RWL).

8.2

Dataflow, databases and data availability

Data from well field monitoring are entered in the database WELLMON installed at the DWA Maun office.
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All water chemistry data provided from any groundwater resource study is entered in the AQUABASE and the main determinants are cations, anions, TDS, Conductivity (EC) and pH.

8.3

Proposal for groundwater monitoring

It is proposed to launch a groundwater monitoring programme comprising a well considered and thoroughly planned approach based on the concept of i) monitoring groundwater in the peripheral area of the delta; ii) monitoring groundwater in the delta area and the broad valley tracts in the southern part subdivided into various typical terrain units. The conceptual outline is discussed below. 8.3.1 Delta peripheral monitoring holes The west side of the delta has a semi-continuous line of settlements. Existing boreholes are shown in figure 8.1. Following assessment of the data history and present status of these holes, it is proposed that a regular monitoring programme be designed to capture changes in water levels and quality along this desiccated western boundary. Existing boreholes not used for abstraction (due to various reasons) might be converted to pure monitoring wells although the approach might entail some concerns. A small number of new monitoring holes may be required to fill any geographical gaps, particularly to the east of the settlement line where drying out is recent. This should provide a north-south gradient scenario, ie a progressively more distal scenario, together with short east-west transects from the line of settlements in towards the ‘retreating’ delta. The need for new boreholes is tentatively estimated at five supplementing existing boreholes that might be dedicated as future monitoring boreholes. The boreholes shall be fitted for automatic data recording. Recent review of the effectiveness and cost effectiveness of monitoring systems (GCS 2001) has indicated a preference for automatic groundwater level recorders, eg in situ “mini-troll”, Eijkelkamp “diver”, Seba “floater” (at least 3,000 BWP). The review also reached the important conclusion that monitoring systems need to be standardised to provide good data comparability. In areas with easy access and moderate/slow variations in water levels manual readings with the ‘dipper’ type including in-situ measurements of conductivity might be the best choice. The south side of the delta, the distal end, has had considerable attention regarding the groundwater situation, as a result of the Maun Water Development Project. Along the Thamalakane valley the original project monitoring holes suffered from vandalism and there was also some difficulty with the manual recording, particularly in the relatively distant localities. As a result the number of monitoring holes has been reduced to a smaller number of ‘pure’ locations (secure sites). Only the two intended development areas in the Kunyere and Gomoti valleys are effectively monitored (in addition to the Shashe wellfield) but in the Gomoti valley elephant damage is a problem. The installation of new monitoring holes is not envisaged but serious consideration must be given to increasing the security of the original project monitoring system. Similar equipping of the more distant monitoring holes, which are sometimes difficult if not impossible to access would considerably add to the data base. Selection of holes for ongoing monitoring should be based on geographical location, to give a meaningful spread of data, and also on holes for which there is the best continuous record, going back to installation in 1996. As abstraction demands are heavy and increasing in the Thamalakane valley where the groundwater is dependent on outflow of considerable variability, it is recommended that not
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only the change in surface water level be monitored but also the relationships of the upper shallow aquifer with the deeper aquifers. It is known, for example (WRC 2002, 2003) that there are three aquifers, an upper, shallow, sandy aquifer below which lies a semi-confining fresh water aquifer from about 35 to 70 m. Below this, lies a saline water aquifer (Figure 8.2 a).

Figure 8.2 - Thamalakane valley aquifers. 1 – Fresh rapid annual recharge from river, 2 – Fresh slow recharge, 3 – Saline. For further explanation see text.

The present tentative indications are (Linn, Water Resources Consultants, personal communication) that although the shallow aquifer recharges very rapidly when there is surface flow, the response of the lower aquifers is sluggish, with the suggestion that they are in a state of disequilibrium, probably having been equilibriated to the good recharge of the 1970s. The danger is that fresh water abstraction from the lower of the two fresh water aquifers may lower the water level below that of the saline water adjacent to the recharge zone, with the result that the higher head of the saline water will cause saline underflow up below the zone off fresh water abstraction. Two nested systems are envisaged; each being a cluster of three pipes which sample different levels within the water body. Water quality sampling at 1 m intervals during drilling will allow determination of the dimensions of the aquifers and identify suitable depths for ongoing monitoring. The choice exists between three closely spaced separate pipes (ie 3 x 2 = 6 drills) or three pipes emplaced together within a larger single hole (ie two drills with larger diameter). The eastern/north eastern flank of the delta has very few boreholes. The groundwater scenario is virtually unknown here and to complete the encirclement of the delta it is proposed that a system of monitoring holes be emplaced, similar to that on the south/south west side, to give a transect from the proximal to distal end of the delta, together with short traverses at right angles to this line. A tentative estimate is for 6 to 8 holes. Conclusions for the delta fringe area are thus to search for existing boreholes suitable for long term monitoring, ie without impact from existing or likely abstractions nearby and supplement these with a tentative estimate of 5 dedicated monitoring boreholes at the western fringe, 2

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nested monitoring boreholes in the southern part (2 x 3 drills or 2 larger diameter boreholes) and 6 to 8 dedicated monitoring boreholes in the eastern/north eastern part. Water level readings – either manual or automatic – shall be carried out at adequate frequencies to capture variability in water level within the dry and flood seasons and trends from year to year. In-situ measurements of conductivity (less frequent than water levels) shall be part of the programme. 8.3.2 Delta monitoring holes The study by Dincer and others (1976) used a small catchment bounded on the east by Beacon Island in a seasonally flooded area. It was essentially a one cell model representing the whole delta. Weirs at the entry and exit points were used to determine inflow and outflow. Piezometers were installed at the edge of the flooded area, to establish losses to groundwater, rainfall gauges emplaced and evapotranspiration estimated. The study concentrated on determination of water balances and volume-area relationships (in the event, the flood water failed to reach the catchment soon after the system was installed, terminating the monitoring programme). The extension of the water budget to the entire delta was rightly criticised. It is only representative of a particular type of terrain unit within a mosaic of different units. It is proposed that a satellite image study is conducted to divide the delta into terrain units, and similar small catchment studies be made in each of the units in the seasonally flooded area in order to provide a more representative statement regarding water budgets within the delta as a whole. Because the groundwater level is high in such situations, obviating the need for drilling, it is a relatively inexpensive way of accessing, in significant quantity, important hydrogeologic and hydrologic data representative of the different terrain units within the delta mosaic. Thus such small catchment studies offer good prospects for more representative water budget estimations. HOORC’s catchment study adjacent to Chief’s Island already provides one further example. In the southern part of the lower delta, ‘broad tract’ valleys occur (eg the Xwaaqa, Xudum, Marsiba). These are wide and flat, with small channel form features developing in the lower reaches as the surface flow becomes integrated towards the Nxaragha and Kunyere, ultimately flowing to Lake Ngami. Flooding of these valleys has generally retreated and melapo cultivation accordingly reduced and eventually abandoned. Hand dug wells on the valley floors have been progressively deepened to access the lowering groundwater level. Running sand is depth limiting for such efforts. The situation has become critical for settlements in these valleys and north of the buffalo fence the flood fed riparian woodland is increasingly stressed. From casual observations, the groundwater level appears to be lowering at a rate of about 1 m each year in the absence of flooding. It is imperative to monitor this situation and to make clear statements regarding the effects of diminished flooding in the lower delta. (There is a tendency for the pro-development/abstraction lobby to be of the opinion that upstream abstraction will only have a miniscule effect, mainly in the lower delta (present writer’s emphasis), without full appreciation of the reality, ie that the effects of flood reduction are progressively amplified towards the distal areas). It is proposed that one long profile of a valley be monitored to quantify clearly the effects of flood retreat. This can be done at relatively low cost using piezometers in the upper reaches where the groundwater level is higher (hand drilled with bailer, then jetted where the water level is deeper and declining more rapidly). Downstream where levels are deeper and declining more rapidly, small holes drilled with a lightweight rig (eg Water Surveys Botswana “Eureka Portarig” are appropriate for the completion of the long profile transects - see Appendices 10 and 11 for details).
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A similar long profile transect should be placed in a morphologically comparable valley on the north side of the delta to provide adequate comparisons. In the lower reaches of the ‘broad tract’ valleys described above and in the Nxaragha and Kunyere valleys, there is a clear need for examining and monitoring cross sections of the system, where a potentially serious situation is evolving with respect to groundwater levels and quality. This is happening under the natural conditions of diminishing flooding. The groundwater level is dropping below the valley floors (reaching around 15 m in the lower Kunyere). The levels are dropping even faster below the transpiring riparian woodland (Figure 8.3 a).

Figure 8.3 - Lower Kunyere aquifers. 1- Fresh, 2 – Saline. More explanation, see text.

They have lowered to the extent that the level of the saline water in the interfluve areas, formerly lower than the fresh water levels, is now approximately the same. Further lowering of the fresh water levels (Fig 8.3b) will result in a saline head, expected to lead to a situation in which the saline water underlying the fresh will be driven to underflow upwards into the valleys and riparian zone (Linn, Water Resources, personal communication). The ecological implications are disturbing. “Miniscule” reduction in flooding can effectively tip the balance towards major deleterious changes. It is proposed that two cross sections be monitored, with drilled holes – one in the saline interfluve area on either side, one in the riparian woodland on either side and one in the centre of the valley. A similar system should be placed in a northern ‘broad tract’ valley, to provide the contrast. To complete the data spread, monitoring piezometers should also be placed for monitoring where groundwater levels are already known to be very stable, both in areas of saline and fresh water.
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8.3.3 Sedimentology While the importance of the effects on river and flood advancement of varying depths of the unsaturated zone are now generally appreciated, albeit as yet unquantified, the importance of surface and near surface sedimentology has lacked attention. At the simplest level, a sequence of satellite images tracking flood and river extension clearly shows great irregularity, fast in some places, slow in others. This expresses changes in the surface sediments. Where they are sandy and permeable, losses to groundwater are rapid and flooding or river extension slow. Where the surface material is less permeable silts and clays, there is rapid flood and river advancement and correspondingly less water enters the groundwater system. A good example of this was provided by the Nxaragha/Kunyere system following the extremely good wet season of 2000. This resulted in extensive flooding in these valleys to the north west of the Kunyere Fault, with drainage to Lake Ngami, filling it to an estimated 60% of its area. It was said, in 1983 by Shaw, that the lake “plays an important part in the economy of northwest Botswana. It supports a small but growing commercial fishing industry, whilst visitors come to observe, or in some cases to shoot, the abundant bird life. The surrounding lake flats support in excess of 30,000 cattle…”. The lake had been completely dry for at least a decade prior to the impressive 2000 flood. The ease with which the water reached the lake is clearly attributable to the several metres of silty clay which caps the underlying more permeable sand. This allowed the flood waters to travel fast without much loss to the substrate (in desperate need of recharge, as described above). This is in complete contrast to the Thamalakane valley where flooding is slowed down by rapid recharge into the permeable, sandy surface horizons, up to 35 m thick (resulting in up to 10 cm rise of groundwater level per day; Lynn, personal communication). Clearly the surface or near surface sediments play an important role in the extension of the surface water and the recharge of the substrate. Drilling or augering provides an essential opportunity to gain clear knowledge of the nature of the sediments, knowledge which is essential for the interpretation of the groundwater monitoring results.

8.3.4 Discussion The programme of monitoring proposed above is comprehensive. It provides a comprehensive data spread for modelling, it addresses key issues both scientific and socio-economic and it entails an appropriate range of technological levels with considerable emphasis on low cost piezometry and lightweight drilling. Prioritisation in terms of the timing of the installations requires consideration. While continuous monitoring resulting in unbroken data series should be targeted, past experience has shown that complete continuity of data is unlikely to be achieved for a variety of reasons. There is recent understanding of the cost-effectiveness of automated systems. Conversion of key existing monitoring sites presently with manual reading to automated recording can provide a substantial increase in the data at low cost. Upgrade of automated recording to more interference-proof systems would be similarly cost-effective at essential sites. It may be possible to increase the protection of vulnerable piezometric systems by education of the local communities and their involvement with recording (periodically monitored by DWA staff). Nevertheless some data losses are to be expected and must be accommodated. Evaluation of the data points becomes important with respect to the level of protection. In areas where flooding is protracted, the difficulties of monitoring are logistically severe. Concession holders in these areas (often fly-in localities) already have excellent capability with respect to logistical issues. They are well placed to offer secure sites. Environmental monitoring is invariably a necessary component of tenders for concession management. There is a strong
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emphasis on vegetation and wildlife observational monitoring. Rainfall and water levels are sometimes monitored out of general interest, but this is unsystematic, uses varying methodology and is discontinuous as the concessions change hands. There would seem to be considerable scope for the acquisition of low-cost data from concession camps, data which would be very valuable if (a) there was systematisation of data collection (rainfall, water levels, piezometry), (b) provision and installation of equipment/systems by DWA and (c) this monitoring were made a compulsory component of the environmental monitoring by concession holders. Collaboration with DLUPU and Land Boards would be needed in order to introduce such monitoring requirements from the holders.

8.3.5 Costing for drills Based on experience from actual drills in Botswana the installation of a fully equipped monitoring hole is extremely expensive. An 80 m hole, drilled by a conventional rig, for example, is likely to cost nearer 200,000 BWP than 100,000 BWP. Even following the old Uniform Rates, a local driller is likely to charge in the order of 100,000 BWP, despite free provision by DWA of all materials required. Quite clearly the monitoring programme proposed above must utilise (a) existing holes and (b) new holes drilled by much cheaper systems if it is to come realistically within the monitoring programme budget. Piezometric systems have been successfully used by Water Resources Consultants in the Delta. (see Appendix 11 for details, abstracted from WRC 2002) at an estimated cost of around 600 BWP/hole (Linn, WRC, personal communication). Such systems are appropriate where very shallow holes are required. For deeper holes up to 75 m and where the water levels are declining rapidly, a lightweight, low cost drilling rig, the Eureka porta-rig has proven capabilities. (See Appendix 10 for details, including estimated costing of a proposed 45 hole project in the Delta.) The use of these low cost systems could adequately provide for the requirements of the monitoring programme as described above.

8.4

Implementation

The implementation requires thorough consideration and dedicated effort throughout the phases of evaluating suitable existing boreholes to be converted to long term monitoring sites, detailed site planning of new and additional boreholes in the peripheral areas of the delta and the network of piezometry drills in the delta proper, design of drills and casings, tendering of drilling operation, supervision of contractor and final implementation of the programme. A well considered approach utilising local experiences from the groundwater and geological surveys and lessons learnt from previous groundwater monitoring programmes will be essential for long term sustainability of the monitoring programme. The implementation will have the character of an iterative process. Consequently a flexible approach will be imperative. It is recommended to mandate a small task force the responsibility of working intensively with the implementation of a cost-effective programme within the frames of the overall budget. The task force shall be supported with technical assistance from the consultants. The setup is further discussed in section 13 of this report. The most uncertain part of the budget is the cost of drilling. Through consultations with the DWA groundwater section in May 2004, new drills would be decided among offers from private contractors based on a tender comprising technical design and specifications prepared by
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the task force. If the offers are found unacceptable in technical and economic terms, DWA will be able to carry out the drills through their own drilling section. Whenever the monitoring boreholes are established and the monitoring is entering a routine mode with modest frequencies of site visits including automatic water level recorders in the most remote places, the additional workload might add up to a fairly limited number of additional man months per year for the field staff. The cost cannot be estimated for the time being but most likely it can be accommodated within a modest budget for operational costs compared to the cost of implementation. It is recommended that DWA management shall prioritise the long term sustainability of the programme through an adequate operational budget and logistic support, otherwise an ambitious investment in establishing the programme will be wasted. At present a DWA staff person is dedicated to carry out the existing monitoring programme of the Maun wellfields and his responsibility might be expanded to cover the ODMP monitoring tasks.

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9 Assessment of Water Quality Monitoring
This section focuses on water quality monitoring of the surface waters flowing into the delta and the water quality within the delta. In this context the term water quality is defined to be the major chemical parameters determining important processes in the ecological function and the utilisation of the delta’s water resources.

9.1

Existing monitoring and assessments

Previous monitoring of water quality parameters in the surface waters of the delta has been scarce and scattered to a few project specific studies, dissertations and research works. DWA and other Government Institutions have not carried out systematic or routine monitoring of water quality parameters and consequently long time series of basic water quality parameters are absent. One reason is the high heterogeneity in the delta in terms of spatial and time variations making a routine monitoring programme on water quality parameters difficult or even meaningless unless substantial efforts are directed towards identifying and determining the variations. As part of the OKACOM diagnostic assessments in 1997, a review of water chemistry and water quality was carried out (Warmeant, 1997). The review summaries the findings of four to five studies mainly from the Jao-Boro River system (prepared by Cronberg G, Gieske A, Martins E Nengu J. Stenstrom M in 1992, 1995,1996), and studies on chemical sedimentation (precipitation) in plots of the Maunachira River and Jao-Boro River carried out by TS McCarthy and J Metcalf and from SMEC Southern Okavango Integrated Water Project (1987). In 2002, DWA initiated a study of the local impact on the water quality near some 116 camps situated in the delta and along the Chobe River (Okavango and Chobe Pollution Study - an Inception Report has been prepared, but no copies are available.) The intended purpose is to assess the water quality upstream, in front of and downstream the camps. Three annual sampling rounds will be analysed for standard water supply parameters and bacteria content (pH, EC, TDS, Ca, Mg, Na, K, Cl, SO4, NO3, F, CO3, HCO3, Fe, Mn and faecal Ecoli and Faecal Streptococci). The laboratory analyses are carried out at the DWA laboratory in Gaborone. The data are stored in the database AQUABASE also used for groundwater chemistry data. The study of the local pollution impact from the camps (including bacteria contamination) has to face difficulties separating the natural turnover, pulses from decomposition in the aquatic system and animal dung from the local impact of the camps. Interpretation of pollution impacts from the camps will be very difficult to determine based on the survey, and it is recommended that the efforts shall be reconsidered and scaled down to essential and likely hot spot areas (if these exist in terms of local water pollution impacts). In June 2000, under high water conditions a water quality survey in four sub-areas of the delta was conducted as part of the Rapid Assessment Programme (RAP 27). The programme included in-situ monitoring of temperature, conductivity, pH and dissolve oxygen with hand held instruments. The survey was repeated under low water conditions in 2002 but not yet reported. At the HOORC Camp site on the Boro river (middle part) conductivity, pH and temperature was measured for several years and variation in the pH, conductivity and oxygen content (Sethebe).
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The main characteristics of the water quality findings from the Okavango Delta from the various studies are condensed into Table 9.1 below.
Parameter Basic Parameters Typical values/ characteristics of water chemistry in the Okavango Delta pH in surface water is in the range of 5.6 – 7.7 (but higher in the groundwater - in Maun up to 9.8) Surface water temperature in the inflow varies between 17-18 0C in July and 29 0C in January and 3-4 degrees higher at the southern fringe part of the delta Dissolved Oxygen is close to saturation in flowing waters but can be substantially lower in stagnant pools and wetlands reflecting various natural conditions. Reported fish kills in Guma Lagoon might have the root causes in natural induced flushing of organic rich waters from the Papyrus mats into the lagoon (RAP 27) Salts (anions/cations) The surface waters in the delta are fresh with low content of salts in the order of 20 mg/l of TDS (Total Dissolved Solids) and Conductivity of 3 8 mS/m but gradually becoming slightly more salty southwards and considerably higher in isolated pools of stagnant water due to evaporation. Salt aggradations are found in soil matrices in islands and constitutes a complex interaction with vegetation and evaporation The Okavango River and open waters are low or even very low in nutrients (N and P) with levels recorded to be in the range of 0.4 – 1.5 mg/l of Total N and 0.02 – 0.08 mg/l of Total P. The content of inorganic N (NO3-N and NH4-N) indicates a fast biological uptake. The low level of nutrients is also in harmony with high transparency of the waters in the channels. The nutrient levels indicate oligotrophic conditions while isolated waterbodies can be characterised as mesotrophic – eutrophic Heavy metals A few scattered analyses of heavy metal contents in surface water have been done. Due to the pristine conditions of the catchmemt area, the content is low and likely to reflect natural geological conditions. Analysis of low levels of heavy metal in water samples will require significant experience and laboratory skills in providing reliable results Spraying with insecticides combating the tsetse fly (eg in 2001) and the herbicide paraquat (1974-82) against infestation of the Kariba Weed (Salvinia) has taken place. Some specific investigations are done in order to determine residues in the environment.

Nutrients

Persistent and toxic compounds introduced as anthropogenic chemicals

Table 9.1 – Summary of water quality characteristics, based on available information from Warmeant, 1997, interview with DWA staff and HOORC staff (2003).

9.2

Need for Water Quality Monitoring

The water quality entering the delta from the upstream part of the Okavango River determines the conditions in the delta itself. It is well founded to start a long term systematic monitoring of

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essential water quality parameters at Mohembo including basic parameters, anions/cations and nutrients. A similar long term programme could be of value in the southern most part of the delta at the Boro River (Junction) near to Maun as well as the North Gate at Khwai River indicating the water quality as a function of a number of processes in the delta. The monitoring shall be carried out in parallel with the discharge measurements enabling mass flux calculations of the main constituents through the delta.

Figure 9.1 – The Boro Junction (7412) in October 2003 (left) and North Gate on the Khwai River (7545) in August 2003

In the delta itself, high evaporation rates and subsequent precipitation of inorganic solutes are the main chemical processes and of utmost importance to the ecological functions. The solutes in the surface water enter the aquifers and eventually determine the groundwater quality also in the fringe area, which is of vital interest to the domestic water supply. The integrated hydrologic model can indicate the overall flow patterns and thus supplement the assessment of the main distribution of solutes in the delta area. There is a well founded reason for determining the salt content in the surface water through easy-to-conduct in-situ measurements of conductivity and temperature. Conductivity is a robust parameter indicating the salt content. Furthermore pH is proposed to be included as a parameter. The locations for in-situ measurements shall coincide with routine monitoring of water levels and flow discharge. It could be considered to include dissolved oxygen as a parameter. Oxygen probes in hand held equipment are sensitive to handling habits and rough conditions (as the actual conditions in the delta). Most likely oxygen probes will introduce a rather proportion of uncertain or even misleading results. As an alternative, field measurements using the oxygen field test kit (Winkler titration) could be considered, but are left out of the proposed setup in the delta in order to keep the monitoring manageable for the DWA field staff.

9.3

Proposal for Water Quality Monitoring

The proposal for a systematic and long term monitoring programme is summarised in Table 9.2.
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The proposal reflects the following considerations

Location Mohembo

Type of Water Quality Monitoring In-situ measurements

Parameters to be analysed Conductivity, temp, pH

Frequency weekly

Comments Mohembo is a permanently staffed station and carries out daily measurements of Q Mohembo shall collect the water samples in parallel with in situ measurements. The samples are transported to the laboratory in Maun Boro Junction is visited several times a week by DWA staff for discharge measurements and in-situ sampling can be added to the tasks of the team DWA staff to collect water samples in parallel with insitu measurements. The samples are transported to the laboratory in Maun

Mohembo

Water sampling + lab. pH, O2, TSS, analysis in Maun TDS, WQ standard* , TN, inorganic-N, TP, ortho-P Conductivity, temp, pH

twice a month

Boro Junction In-situ measurements (7412)

weekly

Boro Junction Water sampling + lab (7412) and analysis in Maun Khwai River North Gate (7545)

pH, O2, TSS, TDS, WQ standard* , TN, inorganic N, TP, ortho-P

twice a month

Measurements In-situ measurements at stations where discharge is made on regular basis (appox 20 stations)

Conductivity, temperature and pH

in sequence with discharge measurements (~monthly)

In-situ measurements of conductivity and pH are introduced as routine parameter for the DWA field team staff and shall be carried out whenever the station is visited for discharge measurements

Note *) WQ standard is usually parameters for water supply analysis (cations and anions)

Table 9.2 – Proposal for a systematic monitoring programme on water quality parameters to be carried out by DWA • Key water quality parameters shall be monitored on a routine basis in a systematic way • The water quality parameters selected shall be essential for determining key functions of the delta and provide long term time series enabling assessments of trends due to changes in the upstream area and within the delta • The monitoring programme shall be balanced with the present and near future capabilities of the DWA organisation (field staff, laboratory facilities, data processing, etc)
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• The monitoring programme shall be in line with the DWA responsibilities of collecting water quality parameters in parallel with hydro-climatic data • The monitoring programme shall take into consideration the logistic constraints in carrying out the programme • Additional and more intensive target monitoring programme (campaign monitoring) can be introduced without interfering in the systematic programme. The laboratory capability in DWA Maun is limited in terms of manpower and at present not able to carry out analysis of low level contents of nitrogen and phosphorus. The analysis of the full range of proposed parameters can be carried out at the laboratory at HOORC or as an alternative at the DWA laboratory in Gaborone. This will impose additional constraints in the logistic arrangement. It is recommended to find an arrangement with the HOORC laboratory until the laboratory in Maun is capable of the analysis. In May 2004 DWA appointed two laboratory technicians to Maun. In the detailed planning of laboratory involvement the actual capability both at HOORC and DWA Maun shall be taken into consideration. The programme will require additional equipment and staff resources as indicated in Table 9.3 and Table 9.4.
Equipment Water sampler for Mohembo Estimated no. 1 Comment Water sampler is needed for Mohembo due to the depth of the river. At the Boro Junction and the Khwai River the sampling shall be carried out by a simple bucket 1 instrument permanent for the Mohembo staff + 4 for the field staff teams + 2 backup

Conductivity meter including temperature readings / automatic compensation (hand held instrument) and pH meter Dissolved Oxygen Meter (O2) (hand held instrument) or alternatively a oxygen titration field kit Flasks, cool boxes for water sampling at Mohembo / Boro Junction / Khwai River North Gate

7

3

1 instrument (or field kits) for the Mohembo staff + 1 for the Boro Junction/Khwai readings + 1 backup Exchange of the field sets between the field staff and the laboratory will ease the logistic arrangements and transport constraints

8 sets

Table 9.3 – Outline of additional equipment and activities as part of the proposed water quality programme

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Okavango Delta Management Plan Activity for DWA staff Frequency Comments

Hydrology and Water Resources

In-situ measurements at Mohembo and Boro Junction field staff Water sampling at Mohembo, Boro Junction and the Khwai River Transport of samples to Laboratory in Maun (within 6 hours of sampling) Conductivity and pH readings in-situ for the field staff

weekly

The measurement and filling in the field form can be carried out with marginal time consumption (15 minutes per reading) The sampling can be carried out as part of the regular discharge measurements. Additional time requirement will be marginal (15 minutes per reading) Reliable dedicated transport will most likely be required The additional readings and form filling will slightly prolong the time required at each station The analysis will add to the workload in the laboratory The readings from the locations shall be entered into AQUABASE and HYDATA. Data assessment of raw data entries shall be part of the routine work. The introduction of the programme needs coordination and training in handling of the in-situ equipment and water sampling. Follow up as appropriate and quality assurance essential

twice a month

twice a week

in sequence with routine discharge measurements 3 x 26 samples per year monthly

Laboratory analysis at DWA Maun or alternatively at HOORC Data filing and data assessment

Coordination, training and quality assurance

monthly – annually

Table 9.4 – Overview of major staff requirements introduced as part of the water quality programme The water quality programme has the advantage that the staff resources and facilities are to a large extent in place and the programme fits into the existing DWA field activities and logistic setup. In other words the water quality programme has the character of an add-on activity rather than a burden of new procedures and duties hampering the implementation of the programme. The field staff will need basic training in handling the instruments for water quality sampling and readings. The training can be carried out as short courses and refresher courses. The amount of laboratory work will be extended but will not be overwhelming compared to the number of similar analysis and thus not critical for the setup. The DWA laboratory in Maun is not be able to handle the full range of analysis for the time being. It is recommended to request HOORC to carry out the analysis until the DWA laboratory is upgraded and extended. In conclusion, the water quality programme can be introduced in a cost effective way and it is recommended to launch the programme as soon as possible.

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10 Assessment of Hydro-climatic Monitoring
The essential climate parameters in hydrologic monitoring are precipitation and evaporation. Precipitation is fairly easy to measure manually but requires the presence of personnel to read and empty the raingauges. Automatic registration of precipitation is a more complicated way to measure the same parameter, giving a finer resolution of the temporal variation. Point measurement of precipitation indicates the rainfall at the spot and will not necessarily be representative for the area distributed rainfall. While there is a degree of spatial and temporal variation in the rainfall over the delta, this is considerably attenuated in the surface water flow distribution. A fine resolution is not considered essential. Evaporation could be measured by evaporation pans but it is the general experience that pan measurements are uncertain. The common approach is to calculate the potential evaporation (Ep) value using formulae (eg Penman formula) including parameters such as temperature, wind speed and solar radiation.

10.1 Network status
In the Okavango Delta and surrounding area five DMS stations are located including Maun in the southern part of the delta and in Shakawe in the Panhandle. These two stations have the most complete records of climatic parameters including evaporation measurements. The additional three DMS stations in operation are at Shakawe, Gumare, Nokaneng and Sehitwa. Altogether the five DMS manual operated stations will cover the fringe area and shall be considered as primary data sources on climate parameters. Data from the stations have been evaluated in EHES, 2003. As stated previously (Chapter 6) DWA has 8 DCP stations, 7 located in the Delta, and one at Mohembo. All stations are equipped with rain gauges of the tipping bucket type. It is recommended to include additional climatic parameters at three stations (the DCP in Mohembo, Xugana and Kwihum). Due to vandalism and lack of maintenance no data has been produced so far. A more detailed description of the DCPs is found in Chapter 6. The evaporation calculation for the hydrologic model and the standard Penman calculation need access to the climatic parameters: temperature, humidity, wind speed, solar radiation and precipitation. These parameters are or should be measured at 3 of 8 DCP stations located in the delta. At the DMS stations in Maun and Shakawe evaporation data are available. Due to the fact that SADC is running a parallel DCP in Mohembo and the proximity of the DMS station in Shakawe there is no need for the climatic sensors at the DWA owned DCP and the station can be removed and used for spare parts in other stations.

10.2 Proposal for upgrading and rehabilitation
It is recommended to bring the DCPs back into operation at locations where there is a fair chance that the stations will be unaffected by human or animal interference. New solar panels and batteries have to be procured and damaged sensors have to be changed. The DCP station at Xugana has to be back in operation so the extended measurements of Hydroclimatic parameters can be provided. The Kwihum station including climatic parameters is irreparably damaged due to vandalism. If the climatic sensors can be repaired it is recommended to remove the platforms to Xo Flats. If
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the sensors are permanently damaged new climatic sensors shall be procured and installed at the Xo Flats DCP. In this way there will be two stations in the delta with extended climatic parameters supplementing the DMS stations both north and south of the delta. This is sufficient and it is not advisable to erect more specialised stations before the existing ones are in operation and have demonstrated that usable data can be derived. The precipitation monitoring network covers the fringe area and most of the delta well. There is a lack of raingauges in the south western part in the dry valleys and gaps in areal distribution. It is proposed to distribute 8 raingauges as a secondary network. The exact location shall be determined with a preference for secure sites (near lodges where arrangements for supervision shall be made) and access to the site. A tentative proposal for locations is depicted in Appendix 7. The total network and recommendation on upgrade of hydro-climatic stations is summarised in Table 10.1.
Stations Raingauges Evaporation (direct measurements or derived on Ep – Penman) 2 (Maun, Shakawe) 2

DMS Stations situated near the Delta (primary network) - existing Data Collection Platforms (DCP) - to be upgraded Additional sites (secondary network) to be established Total

5 (Maun, Shakawe, Seronga, Gumare, Sehitwa) 7 (+ 1 DCP Mohembo – SADC) 8 20

4

Table 10.1 – Summary of existing and proposed upgrade of hydro-climatic stations

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11 Remote Sensing supporting Hydrologic Monitoring
The logistic constraints for all land based hydrologic monitoring in the delta make use of remote sensing techniques attractive and can ideally supplement interpretations of flood levels and dry periods and the overall trends over decades. Furthermore, satellite images can be useful for many other purposes and may therefore be shared with other stakeholders in ODMP. DWA should establish systematic collection of satellite images. MODIS images are free and unrestricted, and provide the best option. These will enable a consistent coverage of the delta, and the detection of the spatial variation in flooding at monthly intervals to follow the flood as it propagates through the delta. Albedo and leaf area index (LAI) should also be included. Satellite images from the Landsat 7 have been used partly for creating the topographical model used for the hydrologic modelling. The topographical model developed by April 2004 includes interpretation of five scenarios from Landsat covering the period 1999–2002. The images were partly made available through HOORC sharing inputs from various research projects and parts have been purchased by DWA specifically for the hydrologic model project. A second supplementary option offering higher resolution is Landsat 7, with one complete scene covering the delta in the dry season and another scene in the maximum flood situation (four individual Landsat scenes cover the delta). Since May 2003 there have been technical problems with the satellite, with errors at the image margins. The usefulness of the images would have to be assessed. The Landsat satellite images can be purchased with a modest budget compared to many land based activities, adding up to approximately BWP6,000 per complete scene or BWP12,000 per year assuming two seasons covered.

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12 Cost Estimate
With reference to the recommendations and tentative equipment list an outline cost estimate has been compiled. The cost estimate is based on procurement of instruments and drills for groundwater monitoring only. The additional time consumption and cost internally for DWA to man the expanded monitoring programme is not estimated at this stage. The programme is designed to fit broadly into the ongoing field activities of DWA, and to make the ongoing activities more efficient and ease the time required for logistics. The majority of the activities shall not add an overwhelming burden of workload when the programme enters routine mode. In the implementation phase considerable man power consumption from DWA must be foreseen in preparing tender documents, evaluation, procurement, installation, training and coordination and QA. Technical assistance in the order of 3 to 4 man months in planning, designing and implementation can be allocated from the international and national staff under the ODMP component 2 and 3. Additional assistance from national specialist(s) might be required and shall be engaged directly by DWA if shortcomings are ascertained in the course of the implementation. In Table 12.1 the main components are listed together with an estimated price for each theme. No attempt in this review has been made to prepare detailed estimates of the cost of the annual maintenance and repair. All the sites are vulnerable to damage, and there is a need to balance installation and maintenance costs. In all circumstances the latter will be relatively high. As an indication of the magnitude, the repair and maintenance costs might be in the order of 10 to 20% of the total procurement cost of the instruments (excluding drilling costs). Taking this value as indicative the amount will add up to some 30,000 USD to be allocated as annual running costs.

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Okavango Delta Management Plan Component Surface water Description

Hydrology and Water Resources Procurement costs (in US$) 40,000

Automatic water level recorders installed at approximately 15 locations and stilling wells established. Procurement of spare parts and upgrade of field equipment including digital cameras for photographic documentation Upgrade and rehabilitation of 7 DCP stations including procurement of 8 additional precipitation gauges and operational software/hardware equipment Procurement of handheld instruments (7 EC, temperature and pH in situ instruments, 1 water sampler, 3 sets of O2 titration kits, 8 sets of flasks/cool boxes) 1 bed load sampler, 1 suspended load sampler, 1 bottom grab sampler, flasks, sample containers, etc. Drills and supply goods for approx 18 boreholes in the delta peripheral areas (900 m boreholes) assuming light drill equipment used (the Eureka porta rig type) and minor costs to rehabilitate existing boreholes for monitoring if feasible Drill and supply goods for approx 40 boreholes in the delta area for piezometry assuming handheld equipment drill (depth up to 20 m) in combination with additional 810 boreholes with the Eureka type for drills in deeper layers Instruments for water level recordings of the dipper type for manual readings (~4) and automatic recordings in remote areas/the delta piezometers (~40); EC and pH instrument for in-situ measurements with sufficient cable length; protection means against damages/vandalism, etc Procurement of Landsat Images (4 scenes per season). Note: Annual cost. Provision included for procurement of 2 years of images (until 2005/6)

HydroClimate

35,000

Water Quality

15,000

Sediment transport Groundwater drills - fringe areas

5,000 75,000*

Groundwater drills - delta proper

60,000*

Groundwater instrumentation

40,000

Remote sensing

5,000 (2 year purchase included) 25,000

Contingencies and unallocated budget for unforeseeable expenses and local contractors for assistance in field work in case DWA workshops and field staff are unable to support implementation Total cost for procurement of equipment and drills

300,000 US$

Table 12.1 - Cost estimate of equipment specified in Chapter 6-11. The cost of groundwater monitoring (*) is very uncertain and based on quotations using light equipment as indicated in Appendices 10 and 11.

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13 Implementation Strategy
The main steps in implementing the recommendations are summarised below. In total, a period of 12 months is foreseen to make the setup fully operational. The implementation plan is depicted in Figure 13.1. The conclusions and recommendations in this report are intended to be presented for perusal and scrutiny of the Technical Committee of the Hydrology and Water Resources component in June 2004. Anticipating an approval of the overall framework of the monitoring outline and the recommendations by DWA shortly after, the implementation shall commence by July/August 2004 and be concluded within approximately one year. In order to achieve fast implementation it is proposed to work in parallel and separately within the four categories of • Surface water hydrology, equipment procurement and sediment sampling • Water quality analysis equipment • DCP installations and upgrading • Groundwater drillings and monitoring In case one of the categories is delayed for whatever reason the others can continue without delays. Groundwater monitoring is particularly complex, and needs more detailed consideration and time to implement.

13.1 Formation of task force
The recommendations as presented in this report are the first step in a comprehensive process. The implementation will require dedicated and well considered approaches and shall utilise data on hydrology and climatic parameters interpreted and entered into an integrated surfacegroundwater model all adding to a deeper understanding of the hydrologic function of the delta. A flexible approach must be the basis for the future process of specification, site selection, installation and mode of operation and the recommendations shall thus be considered as a framework to be detailed and refined. It is proposed to create two task forces charged with the responsibility of implementing a cost effective monitoring programme within the overall budget frames. The task forces can draw on technical assistance allocated from the resources of international and national consultants currently working under the ODMP (Components 2 and 3). The proposed organisational set up is depicted in the chart over.

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Task Force - Surface Hydrology Themes: Surface Hydrology, Sediment, DCP, Water Quality, Satelitte Images Force members: DWA - Hydrology Modelling Unit DWA - Maun/Gumare DWA - Gaborone (Hydrology section)

Hydrology and Water Resources
Task Force - Groundwater Themes: Groundwater

Force Members: DWA - Groundwater section (Gaborone) DWA - Maun DWA - Hydrology Modelling Unit

Ad hoc advice: HOORC Management: Kalaote Kalaote (Project Director) Alasdair Macdonald (team leader)

Ad hoc advice: HOORC

Support from the ODMP Component 2 and 3 consultants allocated to the task forces within the approximately themes and man-time (to be approved): 1) Assistance in equipment specification, DCP upgrade, installation supervision, equipment training, etc (Ole Smith, Monitoring Specialist ~ 0.75 man month) 2) Assistance to groundwater site selection, drill specification, supervision of implementation in Maun (Margaret J McFarlane, Hydrogeologist ~1.5 mm) 3) Assistance to assessment of existing boreholes suitability, mapping, geo profiling, etc (Israel Mabua, Hydrogeologist - 0.5 mm) 4) Assistance to interpretation of surface hydrology, criteria for site selection and future programme for Q-H measurement frequencies, etc (Francis Sefe, Hydrologist - 1 mm) Additional support of 1 to 2 man months may be allocated (based on discussion and approval) from Component 2 - Data Management under the headline of Specific studies to enhance wetland management and monitoring. Assistance allocated to eg preparation of an Annual Monitoring Report on ODMP in a conceptual outline and sediment transport studies.

Technical Assistance

In the beginning, the two task forces shall be assigned to prepare a detailed staff task–time schedule (roster) in order for all involved to have a clear view of who is doing what when with what equipment. This will highlight any need for additional human and equipment resources.

13.2 Specification, final site selection and equipment procurement
Major stepping stones in the implementation are summarised in the tasks timetable (see Figure 13.1). Major steps are: 1. After the approval of the Technical Committee in June 2004 the two task forces of DWA shall be mandated to launch the implementation of the programme. Technical assistance from the international/national staff under the ODMP DWA Hydrology and Water Resources project team shall be made available in the planning and implementation phase. 2. The recommendations in this report shall be circulated to the sections in DWA directly involved in the future programme, and through a consultative process invited to comment and forward ideas for adjustments. The experience from present monitoring (field work, data transmission, data storage, etc) shall be utilised avoiding mistakes and constraints in the logistic arrangements.

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3. The proposed setup and recommendations shall be further detailed and technical specifications of the equipment developed in sufficient detail to make a tender announcement. The technical specifications shall be tailored to the site specific requirements. 4. The technical specifications and tender documents shall be divided into lots as appropriate. The equipment will probably have to be procured from international suppliers. The surface water hydrology part and the DCP upgrading might also face the need for fieldwork and construction work to be carried out by national contractors or by DWA field staff. 5. The groundwater monitoring programme will require thorough planning and site selection. It is expected that the site selection shall rely on a thorough analysis of the geological features and present monitoring boreholes before the best monitoring sites can be settled. Specification on drilling depths, drilling techniques, casings, sealing, piezometry and data loggers shall be specified. It is envisaged that the drills shall be contracted with private companies but DWA can take on the task if required. 6. Following the rules of GOB the procurement of equipment over an assumed value of 10,000 BWP shall be based on tender usually taking about 4 weeks from calls to final selection. The successful tenderer is evaluated on financial proposal in combination with technical criteria. Tender documents are prepared by the DWA task forces. 7. The selected supplier is contracted and the delivery of equipment can probably be within 1 to 2 months. In case fieldwork is needed local contractors are called in for quotations. The technical specifications, site selection and procurement of equipment are foreseen to be in place at the end of 2004, although the groundwater monitoring site selection might be extended a few additional months.

13.3 Installation, operation and training
The installation of the equipment and the effort bringing the monitoring procedures into a routine mode are planned for the first half of 2005. The operational procedures will require instruction and training but essentially the monitoring instruments proposed are fairly easy to operate (except the DCPs). The challenge is to have the dataflow, storage and quality assurance into an established procedure. The tasks are subdivided into: 8. The surface water level recorders and current meters shall be installed and handed over to the field staff thus augmenting the existing network. The equipment selected shall ideally be similar or equivalent to the existing. Training sessions with the field staff in Maun and Gumare will be required. One option is to request the CTA to coordinate the training. 9. A complete overhaul of the routines in water level readings, discharge measurements in combination with the fields staff logistics will be a critical task and should rationalise the entire field work and secure data reliability. The options of using rating curves establishing a correlation between discharge and water level shall pursued although constraints might be faced due to the variable flow and vegetation patterns. 10. The introduction of sediment transport monitoring is foreseen as a joint project between HOORC and DWA. Equipment handling in Mohembo will require instruction in the field. The field sampling shall ideally commence before the flood (no later than December 2004).
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11. The water quality programme needs instruction to field staff in sampling, storage and filling in data logs and data flow, and data storage and interpretation. 12. The DCP stations will require a fairly high level of maintenance skills both in the field, in data retrieval and storage. 13. The drilling of the groundwater monitoring boreholes needs close supervision in the drilling period securing the correct casing, sealing and installation of piezometry pipes. The regular monitoring of the existing boreholes to be included in the network shall be included in regular logistic routes for the field staff and data entries in the database established. 14. The entire setup of the monitoring programme and continuous follow up in the routine mode needs coordination and supervision from the dedicated task forces in DWA.

13.4 Data dissemination
Data provided by improved monitoring is without any use in a wider perspective of the ODMP if the information is entered into a database without easy access and announcements of the options of using the data for other interested stakeholders. Ease of access and dissemination will be coordinated through the HOORC data management activities. It is suggested that an easy to overview annual report on the Okavango Delta Monitoring shall be prepared for and circulated to the key stakeholders, and made available and accessible as a PDF file to be circulated via email or downloaded from the DWA web site (and ODMP web site). The report shall be available within say 4 to 5 months after the last data on the monitoring year are gathered. The monitoring year could either be the hydrological year (1 October to 30 September) or a calendar year. The report shall contain an overview map of the monitoring stations on surface water hydrology, dedicated groundwater monitoring locations, water quality sampling stations and climatic stations. The annual results shall be presented and illustrative time series on selected parameters commented. Model results from the integrated hydraulic model might support the conclusions and findings whenever the model is operational. Excerpts of the actual satellite images procured shall be included in the report.

13.5 Timing and work schedule
The work plan and time schedule is outlined over. The installation in the field is planned to be carried out late 2004 or early 2005, but shall be scheduled according to the actual rainfall and water levels in the delta hampering assess with heavy equipment to be transported overland, and river levels too low for boats.

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Implementation Schedule of Hydrologic Monitoring Upgrading
Tasks Calendar Month Year Inception Phase Review and Outline of Monitoring Programme (This report) Proposal to be presented to discussed at ODMP Tech Com. And approved by DWA Approval of framework of monitoring programme and budget Specification, final site selection and procurement Detail the recommendations in this report - set up the implementation task force Prepare Tech.Specifications for Equipment (Surface Water, Sediment sampler, DCP) Site selection and specifications for groundwater monitoring drillings and boreholes Tendering in one or several equipment lots as appropriate Procurement contract(s) and delivery Installation, training and operation Install equipment on surface water level -discharge network, train and operate Initate and train field staff on sediment transport monitoring at Mohembo Initate and train field staff on water quality programme Upgrade DCP Hydroclimatic stations, follow-up Drill groundwater monitoring boreholes and make monitoring operational Co-ordinate and secure proper dataflow, data storage and data quality Prepare and Initate Annual DWA Monitoring Report Outline of Annual Monitoring Report and dissemination Legend: Main period of activity Part time/extension period 6 7 8 9 10 2004 11 12 1 2 3 4 5 6 2005 7 8 9

1 2 3 4 5 6 7 8 9 10 11 12

Figure 13.1 - Outline of work schedule

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14 Summary and Recommendations
Water is the lifeline to the Okavango Delta. Data on hydrologic and climatic parameters are essential to assess the functionality and long term trends in the delta, and the wise use of the wetland and surrounding area, all part of the 65,000 km2 Ramsar site. As the responsible agency for national water resources planning and development, the Department of Water Affairs (DWA) has an important obligation to provide reliable, comprehensive and systematic information of the hydrology essential in for the Okavango Delta Management Plan (ODMP). A review of hydrologic data collection and data management in and around the Okavango Delta in the context of the Okavango Delta Management Plan (ODMP) has been carried out and recommendations on improved instrumentation, data handling, data storage on surface water, sediment transport, water quality, groundwater and hydroclimatic parameters have been prepared where findings have revealed shortcomings. The design of any monitoring programme shall take its offset in the function and key processes in the hydrologic dynamics and the interference to the ecosystem (time wise and spatial variation) with due consideration of the likely human impacts. Considerable effort has over time been directed towards monitoring programmes on hydrologic parameters, and for many years intensive monitoring of surface water has been carried out. Important lessons learnt from previous and present monitoring shall be taken into account in planning additional monitoring. The following overall objectives and principles for the monitoring programme for the Okavango Delta have guided the review and recommendations: 1. The monitoring programme shall add to sound and reliable hydrologic data to be provided by DWA and to be used for the integrated hydrologic model within and beyond the project period and for other stakeholders active in the management of the delta 2. The monitoring programme shall make possible documenting long term trends in the hydrology, sediment transport and basic water quality parameters 3. The monitoring programme shall focus on the most likely pressures and future impacts from upstream of the delta and changes within the delta 4. The monitoring programme shall be within the scope of DWA’s activities and be carried out as a systematic and long term programme 5. The programme shall be a balance between the cost and usefulness of the data for the future 6. The monitoring shall not have the character of research – that is left for other institutions to carry out.

Surface water monitoring The coverage of measurement stations in the delta is dense. More than 60 stations (past and present) measure water levels with readings of gauge boards, and a few are equipped with automatic chart recorders although the condition of these is poor. Some of the gauge board readings are carried out daily while others are periodic. Discharge (flow) is measured more or less frequently at around 22 sites.

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A total of 8 automatic and remotely operated Data Collection Platforms (DCP) was installed in the delta in 1995. The data are transferred to DMS by satellite and only distributed to DWA if requested. Seven of the DCP stations are installed with equipment for water level recordings and all 8 stations are equipped with raingauges. Two DCPs in the delta have several extra sensors for hydroclimatic parameters. The DCPs are out of order due to elephant damage (3 stations), thefts of the solar panel (3 stations), vandalism and instrument failures or a combination of these. In Mohembo, an extra DCP is installed (SADC-Hycos) measuring several water parameters and hydroclimatic parameters. Data are available from the internet. Precipitation is also measured by DMS at Maun, Shakawe, Gumare and Sehitwa, all in the fringe area of the delta. All monitoring is handled from the local DWA offices in Maun and Gumare. Water level and discharge data are stored in the HYDATA database located in Gaborone. The original measured data and corrected and interpreted data are sometimes mixed. This should be avoided. Previous data series have to be scrutinised and corrected in the further process of setting up the hydrologic model. The following are the conclusions and recommendations on the surface water hydrology • The existing network of water level and discharge stations seems sufficient to cover the delta dynamics in a reasonable way • It is recommended to install robust automatic water level recorders at approximately 15 of the water level gauges where manual readings are carried out today or old chart recorders are not dependable. Inexpensive but robust data loggers are available and can easily be installed on the sites. Together with the DCP water level recorders this monitoring network will cover and uniformly represent the main river system Mohembo, Jao and Boro (10) and Xudum– Kunyere (2). The Thaoge river is covered by 2 stations while the Eastern rivers with uniform and rather small water level variations are covered by 6 automatic level recorders. The final positioning of the stations will depend on the individual needs of spatially distributed data, eg modelling, topographic mapping etc. Any future changes in river routing will influence planning and reconsideration of the locations might be necessary. • All water level gauging sites shall be linked to the national datum level • Although the existing experience with the DCPs is not encouraging, efforts shall be directed towards bringing the DCP stations into function and data received and stored properly. It is recommended to upgrade 6 or 7 of the 8 DCP stations. The extra DCP at Mohembo can be used as spare parts. Stilling wells and proper trenching of the pressure transducer shall be carried out at all stations and solar panels and batteries shall be installed by devices reducing the possibility of simple theft. • It is impossible to make the gauging stations fully animal and theft proof. It will be necessary to carry out occasional repairs and replacement of parts • At least two persons have to be trained in maintaining the DCP stations and collect data from these • Based on a spot test of one discharge instrument and discharge calculation form only it is the impression that the discharge measurements and calculations are carried out satisfactorily and no urgent upgrade of the equipment is needed
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• At least monthly discharge is recommended at all discharge stations in the Delta but the seasonal flow shall be monitored with a higher intensity in flood periods. A recommended frequency requires detailed analysis of the flow pattern and should be a subsequent task • Options of constructing rating curves (dynamic or static) in order to calculate discharge values in between the discharge measurements should be investigated. Calculation of time series with daily discharge has to be done • The daily discharge measurements at Mohembo could be reduced and more detailed measurements could be carried out every second day using the cableway. Rating curves will be sufficient to estimate the water discharge in periods not measured • All measured and recorded data in hardcopy (cross section, velocity, etc) shall be entered in a database making other assessments possible. The database reading shall be carried out at the local office in Maun making first hand quality checks on the raw data possible, and prompt remedial action as required • Historical water level and discharge data has to be further reviewed and quality controlled • Quarterly reporting of data has to be done in the project period and should be continued at least annually as a long term task.

Sediment transport No systematic monitoring of quantities of sediment (bed load and suspended particles) entering or within the delta is in place. The sediment transport is of vital importance to the dynamics of the delta. It is recommended to commence systematic sediment transport monitoring at the Mohembo station in order to assess the variation and the annual load of sediment entering the delta. The monitoring can be carried out by the permanent staff in Mohembo and shall be closely linked to the discharge measurements. A one year initial assessment prepared as a joint project between DWA and HOORC could be valuable and the results evaluated to determine a long term programme. It is also recommended to carry out a one off (initially) post flood campaign in 2004 to sample bed material throughout the delta.

Groundwater Monitoring Approximately 1,000 boreholes are present within the ODMP area and groundwater abstraction is intensifying in the Maun area and at the western fringe areas. Some of the new groundwater well fields have established dedicated monitoring boreholes and water level variations recordings are carried out to some extent. In order to monitor long term trends in groundwater aquifers both as a function of the abstraction of groundwater resources and long term fluctuations in areas outside the area directly impacted, it is proposed to implement a dedicated and well considered groundwater monitoring programme. The sequence of implementing the monitoring will require detailed planning and assessment of the geological structures. The conceptual approach is proposed to contain the following elements
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• Along the western side of the delta a monitoring system has to be designed based on existing boreholes. A small number of new boreholes may be required to fill geographical gaps. • In the southern part of the delta more attention has to be given to existing monitoring boreholes to obtain continuous records of data. • To improve knowledge of the relationship between the upper shallow aquifer and the deeper aquifer, two nested systems are recommend for installation in the southern abstraction area. • In the north eastern and eastern flank of the delta a tentative estimate of 6 to 8 new boreholes is recommended • In the Delta, a number of monitoring boreholes has to be drilled in different terrain types selected from analysis of satellite images and aerial photos • In the southern part of the lower delta it is recommended that a long profile of a ‘broad tract’ valley be monitored to quantify clearly the effect of flood retreat. A similar profile is recommended placed in a morphologically comparable valley on the north side of the delta. • In the lower reaches of the ‘broad tract’ valleys described above it is proposed that two cross sections be monitored in each valley. • To complete the data spread, monitoring piezometers should also be placed where groundwater levels are known to be very stable, both in areas of saline and fresh water.

Water Quality Monitoring of Surface Water Previous monitoring of water quality parameters in the surface waters of the delta has been scarce and scattered to a few project specific studies, dissertations or research works and consequently long time series of basic water quality parameters are absent. It is recommended to commence a fairly simple water quality monitoring programme fitting into the logistic setup of the surface water hydrology fieldwork. The setup has the character of an add on module rather than a new set of procedures to be introduced. The monitoring programme is proposed to comprise long term and systematic monitoring of essential water chemical parameters comprising • Water quality sampling and laboratory analysis of essential water quality parameters at Mohembo (basic parameters, anions/cations and nutrients), at the Boro River (Junction) near Maun and Khwai River at North Gate with a frequency of twice a month • In all stations where discharge is measured on a regular basis the field teams shall carry out in-situ measurements of conductivity, pH and temperature with easy to manage hand held instruments

Hydroclimatic monitoring Precipitation data are measured at five DMS stations in the fringe area of the delta. Inside the delta six DCP stations have to be revitalised for precipitation to be measured.

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Climatic data are measured at two DMS stations in the area. The spatial distribution can be improved when the two or three extended DCP stations are back in operation. Potential evaporation (Ep) calculations can be made from the climatic parameters. • Six or seven of the 8 DCP stations from STS have to be made operational and upgraded. The eighth station at Mohembo can be used as spare as there is installed a new DCP SADC Hycos station. • New sensors, solar panels, batteries, etc have to be procured. • Eight new precipitation gauges should be positioned in the delta mainly in the western part to fill area coverage gaps • Necessary software and field testing kits have to be procured so DWA are independent of DMS. • Contact has to be made to DMS to secure that they will continue operating the relevant precipitation and evaporation stations. Remote sensing Remote sensing and analysis of annually procured satellite images in flood periods and dry periods may add to the interpretation of the hydrologic variation and supplement the land based monitoring. It is recommended on a routine basis to acquire images (eg MODIS, Landsat) as support to the hydrologic monitoring programme. Cost estimate The cost of upgrading the equipment and carrying out the groundwater monitoring drills is estimated to be 300,000 US$. The cost estimate for groundwater monitoring comprises 60 % of the total cost and is the most uncertain part, depending on the actual drill costs in the area. The annual cost of maintenance and repair of the equipment is estimated to be within 10 to 20 % of the capital cost. The overall upgrading should not be implemented until it is assured that this latter cost can be met from the revenue or other budget In addition to the procurement cost, DWA manpower in implementing the proposed monitoring programme will be required. The monitoring programme itself will to a large extent fit into the normal routine of the DWA field staff functions and will not expand the workload dramatically.

Implementation strategy and timing The recommendations in this report will be discussed in June 2004 in the Technical Committee of the Hydrology and Water Resources component under ODMP and shall be subject to approval by DWA. Anticipating approval of the outline of the recommendations shortly after, the implementation shall commence in July/August 2004 and be concluded within approximately one year. In order to achieve fast implementation it is proposed to work in parallel and separately within the four categories of • Surface water hydrology, equipment procurement and sediment sampling • Water quality analysis equipment • DCP installations and upgrading • Groundwater drillings and monitoring

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In case one of the categories is delayed for whatever reason the other issues shall continue as planned. The outline of the equipment and location has been based on the findings at the beginning of a comprehensive process. Data on hydrology and climatic parameters are gathered and shall gradually be interpreted, all adding to a deeper insight of the hydrologic function. A flexible approach from the outset shall be the basis for the future process of specification and site selection. Thus the programme shall be considered an outline for further refinements. It is proposed to dedicate two task forces with the responsibility for implementation. One task force shall be charged with the responsibility of surface water monitoring, upgrading the DCPs, water quality and sediment transport monitoring. The second task force shall be charged with groundwater monitoring. The technical specifications, site selection and procurement of equipment are foreseen to be in place at the end of 2004 although the groundwater monitoring site selection might be extended some additional months. The installation of the equipment and the effort bringing the monitoring procedures into a routine mode are planned for the first half of 2005. The operational procedures will require instruction and training but essentially the monitoring instruments proposed are fairly easy to operate (except the DCPs). The challenge is to have the dataflow, storage and quality assurance in a well established procedure.

Data dissemination Data provided by improved monitoring is without any use in the wider perspective of ODMP if the information is entered into databases without easy access and announcements of the options of using the data for other stakeholders. It is suggested that an easy to overview annual monitoring report on the Okavango Delta Monitoring shall be prepared. The report shall be available within say 4 to 5 months after the last data on the monitoring year are gathered. The report shall contain an overview map of the monitoring stations on surface water hydrology, dedicated groundwater monitoring locations, water quality sampling stations and climatic stations. The annual results shall be presented and illustrative time series on selected parameters commented. Model results from the integrated hydrology model might support the conclusions and findings whenever the model is operational.

Need for technical assistance The major effort in implementing the monitoring programme will be within the first year where substantial input in terms of planning, equipment specification, installation, training and establishing the programme are evident. The groundwater monitoring design will especially require thorough planning in order to create a cost effective programme. Additionally, the concept of an annual DWA monitoring report might need assistance. In the budget for the Danida supported DWA assistance around three man months of international and national technical assistance is scheduled. It is anticipated that additional input (at least from the national consultants) will be required to assist in the implementation of the monitoring programme.

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15 References
Becker, Frederick: Water Demand, Supply and Resource Development (Namibian and Botswana Sector). Specialist Report prepared for OKACOM, March 1998 Dincer, T., Heemstra, H.H. and Kraatz, D.B. 1976 The study of hydrological conditions in an experimental area in the seasonal swamp. Tech. Note No. 20. UNDP/FAO: BOT/71/706. EHES. ODMP – Hydrology and Water Resources. ‘Hydrology Data’ (Working Document, November 2003 (Draft) Gieske, A. 1997 Modelling outflow from the Jao/Boro River system in the Okavango Delta, Botswana. J. of Hydrology, 193, 214-239. GCS (Geotechnical Consulting Services) 2001. Monitoring. Department of Water Affairs, Gaborone. GOB (Government of Botswana) 2002. Groundwater Resources Investigation in the Boteti Area. Hydrogeo (Pty.) and Water Surveys (Botswana). Final Report. GRAS (April 2004). Topographical Model of the Okavango Delta. Draft Technical Report. GRAS – Geographical Resources Analysis & Sciences Ltd. April 2004 Huntsman-Mapila, P. & Wolski, P. Transport and accumulation of the synthetic pyrethroid Deltamethrin in Different Habitats of the Okavango Delta. Mabua, I.D. ODMP - Report on Hydrology and Water Resources – Hydrogeology. Draft Report 23 September 2003. Murray-Hudson, Mike and Parry, Dave: Biophysical Environment (Botswana Sector). Specialist Report prepared for OKACOM, October 1997. Naidu, C K: Improved Monitoring of Okavango Delta, DWA Maun, draft May 2004 RAP 27. A Rapid Biological Assessment of the aquatic Ecosystems of the Okavango Delta, Botswana: High Water Survey. Editors: Leeanne E. Alonso and Lee-Ann Nordin. 2003. Scudder, T., Manley, R.E., Coley, R.W., Davis, R.K., Green, J., Howard, G.W., Lawry, S.W., Martz, D., Rogers, P.P., Taylor, A.R.D., Turner, S.D., White, G.F. and Wright, E.P. 1993 The IUCN (World Conservation Union) Review of the Southern Okavango Integrated Water Development Project. IUCN Switzerland, 543 pp. Sethebe, K.M & Letshwenyo, M. and Huntsman–Mapila, P. Seasonal Variations in Water Quality in the Okavango Delta. SMEC (Snowy Mountains Engineering Corporation) 1990. Southern Okavango Integrated Water Development Technical Study, Department of Water Affairs, Gaborone, Botswana (unpublished). Turton, Anthony, Ashton, Peter & Cloete, Eugene (editors): Transboundary rivers, Sovereignty and Developments: Hydropolitical Drivers in the Okavango River Basin, 2003 UNEP-WHO, Water Quality Monitoring – A Practical Guide to the Design and Implementation of Freshwater Quality Studies and Monitoring Programmes. Editors Jamie Bertram and Richard Balance, 1996

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Warmeant, Poul: ’Review of Water Chemistry and Water Quality in the Okavango Delta’. Specialist Report prepared November 1997 for the OKACOM. WMO (Pub. 680), Manual on Water Quality Monitoring, Operational Hydrology Report no. 27. World Meteorological Organisation, 1988 WMO (Pub. 686), Manual on Operational Methods for Measurement of Sediment Transport, Operational Hydrology Report no. 29. World Meteorological Organisation, 1989 WRC (Water Resources Consultants) 2002 Maun Groundwater Development Project Phase 2, Project Review Report 1, Department of Water Affairs, Gaborone. WRC (Water Resources Consultants) 2003 Maun Groundwater Development Project Phase 2, Project Review Report 2, Department of Water Affairs, Gaborone.

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900 800 700 NB [mm] 600 500 400 300 200 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 100 800 700 600 VNF [m3/s] 500 400 300 200 100 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 90 80 70 60 50 40 30 20 10 0
71.12 Mohe mbo, discha rge 74.12 Boro Junction, discha rge

80.01 Pre cipita tion (a vg Ma un S ha ka we )

VNF [m3/s]

Appendix 1

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60

3

VNF [m3/s]

40

2

VST [m]

20

1

0 1970 60

0 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 3
72.15 Ga e nga , discha rge ] 72.15 Ga e nga , wa te r le ve l

VNF [m3/s]

40

2

VST [m]

20

1

0 1970 60

0 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 3
74.45 Xa kue , discha rge 74.45 Xa kue , wa te r le ve l

VNF [m3/s]

40

2

VST [m]

20

1

0 1970

0 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000

DDH Mstnr. : 75.65 Txaba 75.65 T xa ba , discha rge

75.65 T xa ba , wa te r le ve l

Appendix 2

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#

Muhembo

$
#

Sepupa
#

Seronga

discharge rivers towns roads swamps

$ $

#

$ $
Etsha 6
#

$$ $ $ $ $ $ $ $

Gumare

#

Nokaneng
#

$ $ $
Maun

$
Shorobe
#

Matlapaneng
#

$

$
#

N W S E

Tsau
#

Toteng
# $

Makalamabedi

#

Sehithwa
#

0

50

100 Kilometers

Appendix 3. Existing Discharge measurement sites

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$#

Muhembo $

$ $ $
#

Sepupa $ #

Seronga # $ $ $$ $ $ $ $ $ $ $$ $ $ $ $ $

hydrometric (proposed) DCP hydrometric rivers towns roads swamps

Etsha$ 6 # $ Gumare# $

$ $ $ $ $

$ $ $$ $ $ $ $

$ $$ $ $

$ $

$

$$ $ $

$$ $ $ $

Nokaneng
#

$$ $ $ $ $$ $ $ $ $

$ $ Shorobe # $ $

$

$

$

N W S E

Tsau # $ Toteng # $ $ Sehithwa$
#

$ Matlapaneng $ $ Maun # $ # $$ $ $ $ $

Makalamabedi

#

0

50

100 Kilometers

Appendix 4. Existing and proposed hydrometric water level measurement sites

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$# Muhembo $

$

Sepupa
#

Seronga
# $

$ $

$ raingauge (potential) $ DCP $ climate $ raingauge rivers # towns roads swamps

$
$

$
$ $

$

$
$ $

$
$ $

Etsha$ 6
#

Gumare

# $

$

$

$
$

$
$

$
Nokaneng
# $

$ $

$

Shorobe
# $

Maun Tsau
# $

Matlapaneng
#

#

$

N
Toteng
#

Makalamabedi

#

W S

E

Sehithwa

# $ 0

40

80 Kilometers

Appendix 5 Existing and potential climatic and raingauge sites

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Okavango Delta Management Plan

Hydrology and Water Resources

$#

Muhembo

$
#

Sepupa
#

Seronga
#

DCP rivers towns roads swamps

$ $
Etsha 6
#

$

$

Gumare

#

$ $

$

Nokaneng
#

Shorobe
#

Maun

Matlapaneng
# #

N W S E

Tsau
#

Toteng
#

Makalamabedi

#

Sehithwa
#

0

40

80 Kilometers

Appendix 6. Existing sites where DCP, Data Collection Platforms, type STS, are installed.

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Okavango Delta Management Plan

Hydrology and Water Resources

$#
Muhembo

$
$
#

Sepupa
#

$

Seronga
# $ $

hydrometric (auto) DCP rivers towns roads swamps

$

$
$ $$ $

$ $
Etsha 6
#

$
$ $ $

Gumare

#

$
Nokaneng
#

$

$
Shorobe
#

Maun

Matlapaneng $
# #

N W S E

Tsau
#

Toteng
# $

Makalamabedi

#

Sehithwa
#

0

40

80 Kilometers

Appendix 7. Potential upgrade sites for automatic water level data loggers and precipitation gauges.

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Appendix 8. Surface water stations, tentative list (see notes over)
The Monitoring Network of Okawango Delta - Hydro -climatic data. Version per May 2004 Riversystem 7 1 2 5 Station Station 8 number name MS - Data from Survey 2003/20 Flow + parameters H-Data Q-dataDWA DCP Rain Gauge WGS84 / UTM access Q H H(Aut) in file in file Field Type gauge Zero (msl) Co-ordinates X/Y pere Q H Auto yes Gum B 992.842 583162/7978918

3

6

6

5

5

x x x x x x x x x x

x Ngami Total Nhabe Botheti

A7112 A7122 7134 7144 7154 7215 7225 7245 7234 7524 7535 7525 7544 7545 D 7324 7325 7375 ? 7335 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? A 7425 7414 7424 7434 7435 7454 7444 7464 A7445 7455 7474 7Q.44 7014 7484 7494 7465 7412 7415 7555 A7565 7575 7585 7512 7614 7615 7625 7635 7645 7645 7724 ? 7712 7722 7813 x 7812 x 7814 x 7925 8112

Mohembo Shakawe pere Sepopa Seronga Duba Gaenga pere Letetmetso block Hamoga/Smith channel pere Xugana Mogohelo pere Gadikwe pere Xakanaxa pere Tsaro Khwai Northgate Khwai Guma lagoon pere Etsha lagoon Tubu Bridge dry Ikoga block Cresent Island pere Qusinga upstream seas Qusinga downstream seas Qaakhwa upstream pere Qaakhwa downstream block Small chan. at Qaakhwa pere Weboro block Xhamu upstream pere Xhamu downstream pere Tamachaa dry Kgolalefetshe block Qurube D/stream culvert seas Haya D/stream bypass seas Masepaaphiri dry Xhobegha dry Gandiguni dry Xuru dry Tsau old bridge dry QL3 Kwihum Mosupatsela Madinare pere Gogonte Txichira Palm Tree block Monkey's Skull block Xo Flats Xakue pere Baboon Camp Xaxaba Moumo, DCP (Boro) Moporpta Nxaraga Bukwe seas Thokatsebe seas Pantoon/Boro Junction seas Cross canal Lopis Dxaaba (Txaba) pere Ditshiping seas Daunara Malalakaka dry Moshu Road B.(Marope R. dry Thapegadi-Xudum pere Small Bridge - Xudum seas Beacon Island - Xudum seas Kiri seas Boboo seas Matsebe (Kunyere) seas Lake Bund (Kunyere) dry Toteng (Kunyere) dry Shashe Bridge B.D.F camp Maun Bridge seas Dikgatlong Mogapelwa (Kunyere) dry Samedupi (Boteti) seas

Q Q Q Q Q Q

Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q

Q

Q Q Q

Q Q

Q Q Q Q Q Q Q Q ? Q

Q ? Q

H H H H H H H H H H H H H H H H H H H ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H ? H H H H H ? H

Auto yes yes yes yes yes yes yes yes

Gum Gum Gum Gum Gum A Gum Gum Maun B Maun Maun Maun Maun Gum A Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum

rg

991.051 980.587 977.065 972.59 963.984

589644/7969609 626129/7927088 649249/7918275 665601/7901296 691590/7890572 704651/7889912 697747/7890416

yes

rg

956.483 952.596 951.358 947.617 935.029 972.374

720951/7890492 732460/7875748 736757/7880476 753384/7877269 787524/7878277 644561/7902908 638233/7886023 626136/7858087 636636/7913682

yes yes yes Auto yes

rg

975.565

646498/7911924 629983/7869616 629983/7869616 646359/7893342 645396/7891275 644813/7886317 650480/7893804 650557/7893908 652421/7894821

626093/7856870 628541/7858919 631470/7874244 653349/7767798

Auto yes yes

yes yes

A

rg rg

969.977 971.27 967.958 965.919

664994/7896869 664270/7894352 670050/7883487 675721/7877804

A Auto yes Maun Maun Maun A rg
710321/7842314 712920/7841537 723159/7838424 731453/7835264

yes yes yes

Maun Maun Maun Maun Maun A Maun Maun

945 938.003 932.608 952.851 948.509 939.377 936.311

735281/7816413 743630/7809560 762353/7796428 724319/7879714 734938/7856154

Auto

yes yes

rg

758052/7823699 760182/7814564 663907/7807069 730062/7780528

yes yes Auto yes yes yes Auto yes Auto yes yes yes yes 9 13 22 yes

Maun Maun Maun Maun Maun Maun Maun Maun Maun Maun Maun Maun Maun 8

rg

951.947 951.143 948.873 945.823 945.583 937.488 922.751 929.576 928.533 925.363 922.426 927.541

694835/7837788 697308/7835296 700255/7830773 717811/7828690 713828/7830239 708945/7782101 746389/7771399 703697/7747098 739414/7790741 753811/7786120 746425/7771405 700225/7742131 764020/7774200

75

75

49 75

8

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Notes to list of surface water stations (1) The DWA modelling unit is in the process of verifying data, names, time series,etc. The table might not provide the full overview of all data and stations in the delta (as per May 2004) (2) Names of the stations can have different spellings and the numbers are not full consistent in the data sources (3) Flow and access legend: Pere - perennial flow; seas - seasonal flow with periods of no flow or no water in most years; dry - no flow and water in the river bed for several consecutive years; block - blockages with no access to the gauge board due to vegetation and swamps (4) Q ~ discharge measurements at the station; H ~ manual readings of water level; H(aut) ~ registration of water level with automatic equipment (charts) in function at present or in the past (5) H in file and Q in file ~ records and time series of water levels and discharge from recent years available in the DWA database system in Gaborone (cf. Report - Hydrology Data, April 2004) (6) DWA Field ~ Field work at the station carried out of the Maun or Gumare staff (7) DCP type A: Data Collecting Platform remotely operated with registration of precipitation and water level (pressure transducers). Type B is extended with additional sensors for air and soil temperature, relative humidity, solar radiation, wind speed, wind direction, conductivity, suspended solids (8) Gauge level is elevation amsl to gauge plate zero and the co-ordinates are to the gauge board (in WGS84 system) (9) The river system numbers (4 digits) refer to: First digit ( 7)=Okavango System;second digit=main system in the delta.The system has not been entirely consistent throughout the years (10) Raingauges (rg) are DWA paper chart recorders located in the delta. The actual functioning of the raingauges is uncertain and most likely they are out of function (to be determined) (11) In Mohembo two DCPs are situated. One operated by DWA (not in function) and one by SADC-Hycos (in function)

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Appendix 9. Recommendations to upgrade the surface water monitoring network (see notes over)
3 6 Riversystem 6 7 1 2 5 5 5 The Monitoring Network of Okawango Delta - Hydro -climatic data. Version per May 2004 Situation before 2003/2004 Station Station Flow + Parameters DWA DCP Rain Tentative recommendations - to be refined by task force 8 number name access Q Equipment Programme H H (Aut) Field Typegauge DCP (SADC) sensors to be checked, DCP (DWA) to be Permanent staff - daily H closed. Equipment to be used as spares readings A7112 Mohembo pere Q H Auto Gum B Permanent staff - daily H readings A7122 Shakawe pere H Auto Gum

7134 7144 7154 7215 7225 7245 7234 7524 7535 7525 7544 7545 D 7324 7325 7375 ? 7335 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? A 7425 7414 7424 7434 7435 7454 7444 7464 A7445 7455 7474 7Q.44 7014 7484 7494 7465 7412 7415 7555 A7565 7575 7585 7512 x 7614 7615 7625 7635 7645 7645 7724 ? 7712 7722 7813 x 7812 x 7814 x 7925 Nhabe 8112
Botheti

x x x x x x x x x

x Ngami

Sepopa Seronga Duba Gaenga Letetmetso Hamoga/Smith channel Xugana Mogohelo Gadikwe Xakanaxa Tsaro Khwai Northgate Khwai Guma lagoon Etsha lagoon Tubu Bridge Ikoga Cresent Island Qusinga upstream Qusinga downstream Qaakhwa upstream Qaakhwa downstream Small chan. at Qaakhwa Weboro Xhamu upstream Xhamu downstream Tamachaa Kgolalefetshe Qurube D/stream culvert Haya D/stream bypass Masepaaphiri Xhobegha Gandiguni Xuru Tsau old bridge QL3 Kwihum Mosupatsela Madinare Gogonte Txichira Palm Tree Monkey's Skull Xo Flats Xakue Baboon Camp Xaxaba Moumo, DCP (Boro) Moporpta Nxaraga Bukwe Thokatsebe Pantoon/Boro Junction Cross canal Lopis Dxaaba (Txaba) Ditshiping Daunara Malalakaka Moshu Road B.(Marope R.) Thapegadi-Xudum Small Bridge - Xudum Beacon Island - Xudum Kiri Boboo Matsebe (Kunyere) Lake Bund (Kunyere) Toteng (Kunyere) Shashe Bridge B.D.F camp Maun Bridge Dikgatlong Mogapelwa (Kunyere) Samedupi (Boteti)

pere Q block Q pere Q pere pere pere Q Q Q

pere dry block pere seas seas pere block pere block pere pere dry block seas seas dry dry dry dry dry

Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q

pere

Q

block block pere Q

seas seas seas

Q Q Q

pere seas dry dry pere seas seas seas seas seas dry dry

Q Q Q Q Q Q Q Q Q Q ? Q

seas dry seas

Q ? Q

H H H H H H H H H H H H H H H H H H ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H ? H H H H H ? H

Gum Gum Gum Gum A Gum Gum Maun B Maun Maun Maun Maun Gum A Gum Gum Gum Auto Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Gum Auto Gum Gum Gum Gum Gum

Upgrade with water level datalogger Upgrade with water level datalogger Upgrade with water level datalogger

rg Rehabilitate DCP and install new raingauge
Upgrade with water level datalogger DCP to be upgraded and in function

Minimum monthly visit

Minimum monthly visit

rg
Upgrade with water level datalogger Move DCP to lodge or replace by a simpler system. Q discharge commenced Minimum monthly visit

rg Upgrade with water level datalogger

Upgrade with water level datalogger Upgrade with water level datalogger

A

rg Remove DCP. Water level datalogger to be installed rg
Upgrade with water level datalogger

Minimum monthly visit

A Auto Maun Maun Maun A

Rehabilitate DCP and install stilling well

Minimum monthly visit

rg Upgrade with water level datalogger

Rehabilitate DCP and re-install water level transducer

Minimum monthly visit

Maun Maun Maun
Maun Auto Maun A Maun Maun Maun Auto Maun Maun Maun Auto Maun Maun Maun Auto Maun Maun Maun Maun Maun Maun

Upgrade with water level datalogger

rg Rehabilitate DCP and re-install water level transducer
Upgrade with water level datalogger

Minimum monthly visit

rg Upgrade with water level datalogger, upgrade rain gauge

Upgrade with water level datalogger

Upgrade with water level datalogger (to be removed in dry periods)

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Notes on Recommendations (1) Recommendations are based on a brief analysis of the network without detailed knowledge to the locations and access possibilities. Alterations in the final setup can be expected. (2) A detailed and updated programme on frequency of discharge measurements (Q) and water level (H) readings shall be carried out based on analysis of previous time series and established rating curves (3) A number of 8 existing raingauges exists. Some will be redundant when the DCPs are in operation. The raingauges are outdated and eight new raingauges will be installed in the delta in order to obtain a fair rainfall area distribution. Site selection to be determined with a view to utilising sites under supervision

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APPENDIX 10 - Proposal and Cost Estimate for a Monitoring/piezometer drilling programme using EUREKA porta-rig
High-tech drilling rigs – large, computer assisted rigs, incorporating the most modern techniques and equipment are the most efficient (and expensive) method of completing a borehole. Drilling is carried out with great precision at speed making this the obvious choice for large scale operations such as government sponsored development programmes which require the completion of a target number of boreholes in a given time. These necessitate a high degree of organisation and are usually the subject of a major contract involving often international companies. Such large scale operations require a sophisticated approach using high-tech machines and highly skilled and experienced drillers, plus strong lines of communication and sources of repairs and replacements of machinery and men. Once these programmes are completed the contractors move on leaving little behind in terms of technology or skills transfer. A low cost drilling rig, a purpose designed non-hydraulic rig was developed in the UK by Eureka Pty Ltd., with the capacity to drill holes to 75metres and is suited to use in rural locations by local operators. Constructed from simple, readily available components, for ease of maintenance and repair, it gains its power from a hand started 11 h.p. engine. The mast allows the use of 6 metre pipe lengths and is hinged for compact transportation. The rotary head drive unit is pulled up and down the mast either by a chain system or a combination of engine and winch-brake. After drilling the head swings away to allow pipe insertion. Drilling fluid is filtered and returned to a circulation tank. This compact, lightweight rig can be mounted onto a truck or trailer.

Eureka Porta-rig in operation at Gweta note conversion to air/hammer

Water Surveys Botswana (WSB) propose to use the Eureka rig for the construction of the monitoring and piezometer boreholes within the Okavango area. WSB have completed several projects on behalf of the Department of Water Affairs with the Eureka rig, these include the DWA 1999-2000 Sand Rivers Investigation of the North East District during which some 336 tubewells and monitoring boreholes were constructed into the alluvium. The Eureka rig was also used during the 2000-2001 DWA Hydrogeological Impact Assessment of the Sewage Ponds at Gweta when some 33 piezometers were constructed. The benefits of using the Eureka rig compared to a conventional large drilling unit are not only economic but also environmental in that since no large vehicles are involved there is little impact on the environment. The equipment is simple there is no need of large quantities of fuels, materials, oils, chemicals etc to be kept on site. Repairs can usually be carried out on site or at
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village level and above all operations are simple, anyone can learn to operate the rig following basic on site training. Ancillary drilling staff will be recruited and trained locally from the nearest village thereby creating employment locally. Productivity with the Eureka is good, upto two 20m piezometer boreholes can be completed in a day, provided that the sites are located in relative close proximity and that no hard rock layers are encountered. The deeper monitoring boreholes will take upto one day each to complete. WSB propose to line the piezometers and monitoring boreholes with 50mm diameter uPVC pipe manufactured by Flo-Tech Pipes in Lobatse. The 50mm diameter well lining will allow for the installation of automatic water level recorders if required, alternatively they are well suited for the insertion of manual water level dippers. The piezometers and monitoring boreholes will be drilled using the mud-rotary drilling technique. Muds employed will be bi-degradable and HTH will be jetted into the completed hole with water to accelerate mud degradation. Well screens will be slotted by Flo-Tek in Lobatse with 0.5mm slot size. Borehole diameters will be 4 - 4½” with the exception of the multiple piezometer borehole when a 6” drill diameter will by necessity be employed. The only problems forseen are: • the availability of water for drilling (an estimated 5000 litres are required per monitoring borehole) and in some instances transport distances may be large. • intersection of hard silcrete or calcrete layers within the unconsolidated Kalahari Group succession. Transport of water may cause some delay to the drilling operations. If calcrete/silcrete layers are encountered the tricone bit will be replaced with a sharp drag bit, the swopping and changing of drill bits will slow down the drilling process as the drill stem has to be removed each time the bit is changed. For the multiple piezometers the deepest screen will be gravel packed from the bottom of the hole to just above the top of the screen, thereafter bentonite pellets are inserted to form a seal between the layers. A similar gravel pack and seal process will separate the upper screen from the central one. Mild steel caps and threaded dipper access points will be emplaced on all holes together with a concrete block of 1x1x1m dimension.

Eureka Porta-rig in operation at Gweta

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B. Estimated Drilling Cost and Supply of Material
Item 1 Description (Drilling Activities) Mobilization and Demobilization Inter sites moves Transport of water Rigging up Drilling mud rotary 4 – 6” Casing Installation Top slab including material Sub Total VAT @ 10% Grand Total – Drilling Unit Km Km Km No. M M No. Quantity 4000 1000 1500 45 2150 2150 45 Unit Rate 5 7.50 7.50 500 175 25 500 Total (PULA) 20 000 7 500 11 250 22 500 376 250 53 750 22 500 513 750 51 375 565 125

Item 1

Description Supply of PVC casing 63mm OD x 4.7mm x 2.9m Plain casing 63mm OD x 4.7mm Screen casing 63mm Bottom cap 63mm Press on top cap

Unit

Quantity

Unit Rate

Total (PULA)

M M No. No. M3 M M M Kg Kg Kg Km

1800 350 45 45 30 125 225 225 1 350 1500 500 1500

26 33 14 12 250 10 120 50 25 30 20 10

46 800 11 550 630 540 7 500 1 250 27 000 11 250 33 750 45 000 10 000 15 000 210 270 21 027 231 297

2

Supply of Gravel Pack Installation of Gravel

3

Supply of 6” mild steel Surface casing Installation of the surface casing Supply of bentonite pellets Supply of Drilling mud

4 5

Supply of HTH Transport of material Sub Total VAT @ 10% GRAND TOTAL – Supply Costs

TOTAL ESTIMATED COST (Drilling and Supply)

Pula

796 422

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Okavango Delta Management Plan

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APPENDIX 11 – Planned Methodology for Groundwater Recharge Monitoring (Piezometry)
The two major components of the planned recharge studies are those relating to (1) recharge to the shallow (primarily unconfined) aquifer systems and (2) recharge to the deeper semi-confined to confined aquifer systems. The assessment of recharge to the shallow aquifers will be based primarily on the installation of several experimental sites where both surface water and groundwater data will be collected during flood and non-flood periods. The assessment and characterisation of recharge to deeper aquifers will be based on (a) determination of aquitard parameters through aquifer tests (b) numerical modelling and (c) modelling as well as geochemical methods (isotopes/tracers and tracers). The above components will be undertaken in unstressed (no nearby pumping influence) river reaches; and (b) the potential for salvaging natural discharge through ET and quantities. The major aspects of the planned programme are summarised below. A11.1 - Shallow Aquifer Recharge Studies Investigation of recharge to shallow aquifers will be undertaken through installation of several experimental stations where groundwater and surface water data will be collected. The data collected during both flood and non-flood periods will be used to analyse the magnitude of groundwater recharge to shallow aquifers under natural (undeveloped) conditions. Additionally, the data will form the basis for modelling of the impact of abstraction on recharge rates, primarily focussing on the potential for induced recharge from the surface flood. Two types of stations are planned: (1) specific locations where a series of piezometers (piezometer transects) will be installed to monitor groundwater response to flooding, and (2) where a given reach will be examined to assess infiltration losses over a larger area (water balance). A11.1.1 Piezometer Transect Stations Stations of this type (type 1) are planned for 3 sites in the exploration areas to allow assessment of the spatial variability in recharge. The piezometer transect stations will consist of a series of piezometers installed at various depths in a transect from the river channel to within the surrounding riparian woodland outside of the floodplain. The piezometers will be used to measure the horizontal and vertical head distributions in the aquifer prior to, during and after the flood event. In addition, one stilling well (modified piezometer) located in the channel center will be utilised to monitor river stage. The basic planned layout of a piezometer transect is shown in Figure 1.

1 1 1 1 1 1 Fi

2 B

i L

t f

Pi

t

T

t

Figure 1 – Basic lay out of a piezometer transect station
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As indicated in Figure 1, the transect station primarily consists of a series of shallow (in the order of 2 to 5 meter depth) piezometers extending from the river channel to within the riparian woodland. The spacing of the piezometers will be determined by site characteristics. In some locations (i.e. near the channel), the piezometers will be installed as nests to assess the vertical head gradients. One piezometer will be drilled to the base of the shallow aquifer (approximately 20 meters) to determine its total thickness and allow monitoring of groundwater head in the lowest section of the shallow aquifer. A stilling well will be set up in the centre of the channel with its screened section extending above ground surface to allow continuous monitoring of river stage. Most piezometers are planned to be installed using manual methods (augering/bailing and jetting). The purpose of the transects will be to collect data which are necessary to determine: (a) infiltration losses from the river to the aquifer and (b) definition of the vertical groundwater flow regime.

The following data will be collected at each transect:

1. River stage (continuous monitoring) 2. Groundwater heads and gradients (continuous and intermittent monitoring) 3. Diurnal groundwater fluctuations due to ET (continuous monitoring) 4. Infiltration rates from the river (periodically) 5. Thickness, lithologies and layering in the shallow aquifer 6. Hydraulic conductivity of the shallow aquifer, semi-confining beds, semi-confined aquifers and spatial variations

A.11.1.2 Piezometer Transect Station Site Selection

The general requirements for the piezometer transect sites are as follows: a) High probability of flooding; b) Simple channel morphology and riparian zone development; c) Relatively narrow flood width; d) Absence of silcrete, calcrete or thick clay layers in the shallow subsurface; e) Accessibility during flooding.

A11.1.3 Description of Monitoring Systems/Facilities to be Installed

Piezometers will be used to measure groundwater heads along the transect. The shallow piezometer design for augered boreholes will basically consist of a 50 mm PVC casing with the screened section consisting of approximately 20 cm slotted casing covered with geotextile membrane (i.e. Typvar). The piezometer will be filter packed with clean sand followed by a bentonite seal. The borehole will be grouted at least to 0.5 meters and a concrete pad installed incorporating a lockable steel cover assembly. Piezometer design is illustrated in Figures below.
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Figure 2 - Piezometer design for augered boreholes

Figure 3 - Photo of piezometer screen before installation

For deeper piezometer to be jetted or driven, steel pipe or prefabricated well points with lengths (+/- 20 to 50 cm) of wire-wrapped well screen will be utilized for installation.

A11.2 Piezometer Installation

A crucial component of the shallow aquifer recharge investigation will be the installation of shallow piezometers in depth ranges from approximately 2 to 20 meters (the bulk of most installations will be in the 2-7 meter depth range). It is proposed to use augering and jetting methods to install the piezometers rapidly and with low cost. Basically the shallow piezometers (2-7 m) will be installed by augering while deeper piezometers are planned to be installed by

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jetting (augering may also be used if feasible). Driven well points may also be used for shallow installations to reduce installation time. The planned methods are described below.
A11.2.1 Augering

Augering is basically the use of a manually operated drilling bit to excavate small diameter boreholes. As boreholes extend below the water table, bailing is used as well to deepen the borehole. The piezometer assembly is installed after the drilling is completed. Above the water table, augering is carried out using a riverside or edelman auger head (drilling bit) attached to a series of extensions (Figure 4). The bit is advanced by manually turning the auger bit until it is full, at which point it is taken to the surface and emptied. Representative samples and detailed lithologic logs can be obtained during augering, while undisturbed soil samplers (i.e. split spoon type) can also be obtained during augering. In the unsaturated zone, the borehole stays open without collapse even in clean sand horizons.

Figure 4 – Augering heads

When the water table is reached, temporary casing is installed to prevent collapse. The casing is lowered into the augered borehole and drilling continues by bailing or augering through the temporary casing. As material is removed from under the casing, it is pushed downward. In some cases where the aquifer is clean sand, water must be poured into the casing (maintaining a higher hydrostatic pressure than the aquifer) to avoid sand running up into the casing during drilling. When the desired depth has been reached, the piezometer screen and casing assembly is lowered into the hole and filter pack/bentonite poured into the annular space as the temporary casing is removed. The typical piezometer design is shown in Figure 2 and an example of drilling in progress is shown in Figure 5 below. Depending on specific conditions and based on experience with these methods in the delta, it is anticipated that a single team will complete approximately 20 to 25 meters drilling per day (i.e. installation of four 5 meter piezometers).

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Figure 5 - Installation of a piezometer in Xudum River

A11.2.2 Jetting

For deeper piezometers, installation by jetting is planned to speed the drilling process. Jetting involves the use of water pressure to excavate a borehole. The basic system involves the connection of a water pump and delivery line (wash pipe) to the casing and screen assembly, with a special fitting that allows removal of the wash pipe after the required depth is reached. The basic system is indicated in Figure 6.

Figure 6 - Borehole jetting

Due to the greater strain during jetting as well as the greater installation depths planned for this method, 50mm GI pipe will be used for the casing and screen assembly. Similar to PVC

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piezometers, the screen will be a slotted section of the pipe covered with a geotextile membrane. Stainless steel wire wrap (Johnson type) screens will also be used on piezometers where slug tests are planned. The wash pipe will be a 30 mm GI pipe fitted either with a left hand thread end or bayonet type fitting to allow easy removal after drilling is completed. The drilling fluid will be plain water. Prior to jetting, augering will be completed to the water table and a 110 mm temporary PVC casing installed to reduce water loss to the unsaturated zone. Return water will be re-circulated through a settling pit.

Recommendations for Improved Hydrologic Monitoring

75

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