20090407sac_sedtransporthandout

 

WORKING DRAFT

Fluvial Sediment Transport as an Overlay to Instream Flow Recommendations for the Environmental Flows Allocation Process

Senate Bill 3 Science Advisory Committee for Environmental Flows

Document Version Date: March 20, 2009 Report # SAC-2009-0X

 

WORKING DRAFT TABLE OF CONTENTS

SECTION 1 FLUVIAL SECTION FLUVIAL SEDIMENT SEDIMENT TRANSPORT TRANSPORT ................................................................ ...................................................... .......... 1  SECTION SECTIO N 2 PURPOSE PURPOSE AND AND SCOPE............. SCOPE..................................................................... ........................................................................... ................... 3  SECTION SECTIO N 3 RATIONA RATIONALE LE AND CONTEXT CONTEXT ............................................................................ ................................................ ............................ 4  3.1   TEXAS SENATE BILL 2 .................................................. 3.1 ................................................................................................. ............................................... 4  3.2  TEXAS SENATE BILL 3 .................................................. ................................................................................................. ............................................... 4  SECTION 4 METHODS SECTION METHODS OF ASSESSMENT ASSESSMENT ............................................................................ ................................................ ............................ 6  4.1   HISTORICAL SUSPENDED-SEDIMENT DATA ......................................................... 4.1 ............................................... .......... 6  4.2   HISTORICAL BEDLOAD DATA ................................................................................... 4.2 ....................................................... ............................ 7  4.3   SEDIMENT TRANSPORT MODELS ................................................. 4.3 ............................................................................. ............................ 8  4.4   EFFECTIVE DISCHARGE ............................................... 4.4 .............................................................................................. ............................................... 9  SECTION 5 RECOMMENDATIONS AND EXAMPLE COMPUTATION OF EFFECTIVE EFFECT IVE DISCHARGE DISCHARGE ...................................................................................................... ................................................ ...................................................... 12 12   5.1   EXAMPLE OF EFFECTIVE DISCHARGE ANALYSIS ............................................. 12  5.1 12  5.1.1   Flow-Duration Curve ................................................................................................ 5.1.1 ................................................... ............................................. 14  14  5.1.2   Suspended-Sediment Load........................................................................................ 5.1.2 Load........................................... ............................................. 15  15  5.1.3   Cross-Sectional Data......................................................................................... 5.1.3 Data.................................. ............................................................... ........ 17  17  5.1.4   Bagnold’s (1977) Bedload Model............................................................................. 5.1.4 Model................................ ............................................. 19  19  5.2  ADVOCACY OF THE SAM HYDRAULC DESIGN MODEL.................................... MODEL................... ................. 22  SECTION SECTIO N 6 DECISION DECISION POINTS.............................. POINTS..................................................................................... ............................................................... ........ 23 23   SECTION SECTIO N 7 CONCLUSIONS CONCLUSIONS ................................................................................................... ...................................................... ............................................. 26 26   SECTION SECTIO N 8 REFERENCES................................................................... REFERENCES...................................................................................................... ................................... 27 27   SECTION SECTIO N 9 GLOSSARY........................................................................ GLOSSARY........................................................................................................... ................................... 30 30   SECTION SECTIO N 10 CONTRIBUTO CONTRIBUTORS RS .............................................................................................. ................................................. ............................................. 31 31  

 

WORKING DRAFT LIST OF TABLES

Table 1. 1. Data required for effective discharge analysis at 08114000 Brazos River at Richmond, Texas..............................................................................................................................................14 Table 2. 2. Computations for the flow-duration curve and histogram for determination of effective discharge for suspended-sediment load ...................................................... .........................................................................................17 ...................................17 Bagn old (1977) model and effective Table 3. 3. Computations for bedload transport using the Bagnold discharge for bedload.....................................................................................................................20

 

WORKING DRAFT LIST OF FIGURES

l arge fluvial system, with an emphasis on sediment erosion Figure 1. 1. Conceptual diagram of a large transport, and deposition..................................................................................................................1 mechanisms of fluvial transport................................................. transport ..................................................................2 .................2 Figure 2. 2. Generalized mechanisms Figure 3. 3. Type-I hysteresis loop of suspended-sediment concentrations for two stormflow events ................................................................................................... ................................................ ...............................................................................................6 ............................................6 Figure 4. 4. Effective discharge in its graphical form.........................................................................9 Figure 5. 5. Effective discharge in this example approximately is equal to the bankfull discharge.10 equilibrium in fluvial geomorphology ......................................................11 ............................................. .........11 Figure 6. 6. Concepts of equilibrium Figure 7. 7. Procedural flowchart for recommended computation of effective discharge for suspended-sediment load, bedload, and total load.........................................................................13 Figure 8. 8. Flow-duration curve for 08114000 Brazos River at Richmond, Texas.........................14 Figure 9. 9. Suspended-sediment-load and streamflow rating curve for 08114000 Brazos River at Richmond, Texas ........................................................................................................... ................................................... ........................................................................15 ................15 Figure 10. 10. Suspended-sediment load (SSL) histogram showing effective discharge for SSL at 08114000 Brazos River at Richmond, Texas ................................................................................16 .............................................. ..................................16 Figure 11. 11. Cross section section of 08114000 Brazos River at Richmond, Texas ...................................18 ina ccurately low estimate of effective discharge for Figure 12. 12. Bedload histogram showing an inaccurately  bedload at 08114000 Brazos River at Richmond, Texas ...............................................................21 .............................................. .................21

 

WORKING DRAFT

SECTION 1 FLUVIAL SEDIMENT TRANSPORT The fluvial system commonly is conceptualized on the basis of three dominant processes that operate at various spatial and temporal scales: (1) erosion in the upper source zone, (2) transport in the middle transfer zone, and (3) deposition in the lower accumulation zone (Schumm, 1977) (Figure 1). This macroscopic conceptual model is applicable to many coastal-draining river systems, and all three of the processes; erosion, transport, and deposition; occur to varying degrees in each zone. Sediment-transport processes associated with flowing water begin when earth material is entrained from hillslopes or channel margins and terminate when the material either is deposited or dissolved. Fluvial deposits, including instream bars and benches, floodplains, and deltas, can be either temporary and remobilized or permanent and converted to sedimentary rock over geologic timescales.

l arge fluvial system, with an emphasis on sediment erosion Figure 1. 1. Conceptual diagram of a large transport, and deposition (from Kondolf, 1994; scanned from Brierley and Fryirs, 2005). The transport of material in fluvial systems is segregated into three general modes: (1) dissolved load, (2) suspended load, and (3) bedload (Figure 2). Dissolved load includes chemical constituents moving through the system, and suspended load and bedload are mechanisms of sediment transport. Suspended load refers to particles that are continuously entrained in the water column, and mostly consists of clay and silt, with varying amounts of sand derived from the channel bed during turbulent flows. Sand-sized particulates can either be transported along the  bed during low- or moderate-flow conditions con ditions or in suspension during turbulent flows, thus a subcategory termed wash load is defined by only those particles continuously entrained in the water column (e.g., clay, silt, and organic matter) at all times. Suspended load is important for natural floodplain deposition processes and maintenance of deltaic and estuarine wetland environments.

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WORKING DRAFT Bedload refers to sand grains, gravels, or larger particles that move along or near the channel bed  by various mechanisms (Figure 2). Some references segregate bed-material load from bedload (e.g., Stevens and Yang, 1989), where the former is defined as all particles originating from and exchanging with the channel bed irrespective of the transport mode. Bedload transport is responsible for instream habitat complexity and maintenance, as well as deltaic accretion (formation). The amount of bedload transported by a river assists in forming its channel geometry and its ability to recover from natural or anthropogenic disturbances, including floods and upstream impoundments.

Figure 2. 2. Generalized mechanisms of fluvial transport (from McKnight and Hess, 2000).

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WORKING DRAFT SECTION 2 PURPOSE AND SCOPE This report provides guidance for the inclusion of fluvial sediment transport as a possible overlay to the HEFR approach for determination of an environmental flow regime required by Texas Senate Bill 3 (Senate Bill 3 Science Advisory Committee for Environmental Flows, 2009). Although numerous sources associate the majority of fluvial sediment transport with high-pulse flows, the discussion and guidance provided below are not contingent on an exclusive association of sediment transport with HEFR-based high-pulse flows. In many cases, a healthy sediment regime could be associated either with overbank, high-pulse, or even base flows. Further, it should be recognized that sediment transport processes do not encompass the full  breadth of fluvial geomorphic investigation, but can be readily associated with an environmental flow regime. Section 3 of this report provides a rationale and context to justify inclusion of a sediment transport overlay to the environmental flows allocation process mandated by Texas Senate Bill 3. Section 4 discusses various methods of assessment, including the use of historical data, model equations, and computation of effective discharge. Further, strengths and weaknesses of various methods are presented. Section 5 recommends the effective discharge approach to assess sediment transport at gaging stations and briefly discusses some limitations of this approach. Further, a step-by-step example of the effective discharge approach at a long-term USGS streamflow-gaging station is provided and the use of the SAM hydraulic design model for estimation of effective discharge is advocated. Section 6 identifies several decision points that a  practitioner tasked with a sediment-transport analysis will encounter. Section 7 draws some general conclusions and reinforces various limitations of an effective discharge analysis. This report originally was prepared by the Science Advisory Committee, with comments from the Texas Water Development Board (TWDB). Members of the Science Advisory Committee have reviewed, edited, and expanded the document and have provided recommendations regarding the application of the information and procedures presented in the document pursuant to the requirements of SB 3.

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WORKING DRAFT

SECTION 3 RATIONALE AND CONTEXT As flows increase from base flow to high-pulse flows to overbank floods, rates of sediment transport in the water column and at the channel bed greatly increase. The erosion, transport, and deposition of sediment are as important to the complexity and structural diversity of rivers, riparian zones, deltas, and estuaries as the conveyance of water itself. The balance between the force of water and the resistance of sediment sculpts the many fluvial patterns and shapes that  provide habitats and conditions to which aquatic and riparian species uniquely adapt over ove r time. If only flows are considered, without the associated sediment, then an incomplete assessment of the state’s rivers and bays reduces the likelihood of conservation or rehabilitation. A worst-case scenario might involve high-pulse flow releases that increase rates of habitat degradation. 3.1 

TEXAS SENATE BILL 2

The importance of sediment and river channel morphology has been highlighted by instreamflow activities associated with Texas Senate Bill 2. Also, in a National Research Council review of the Texas Instream Flow Program (TIFP) (2005), it was stated that the section considering  physical processes and sediment required “significant augmentation” to relate them to the hydrologic regime, and that a “thin, single set of analytical approaches” would be insufficient to “address the range or complexity of physical processes.” In response to these comments, the state agencies responsible for the TIFP further addressed physical processes and sediment in the revised technical overview document (TOD) of the TIFP (2008), which contains the following statements: “Geomorphic studies will assess the active channel processes responsible for developing  physical habitats.” “Agencies will develop sediment budgets…” “…geomorphic studies need to be tailored to the specific sub-basin being investigated” “…the lack of geomorphic data for Texas’ rivers is problematic.” “…a monitoring program that collects geomorphic data for major rivers will be required.” The TOD goes on to recommend specific lines of inquiry to address these problems and achieve  program goals. 3.2 

TEXAS SENATE BILL 3

Texas Senate Bill 3 mandates that locally based basin and bay expert science teams (BBESTs), with consultations and support from the Environmental Flows Science Advisory

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WORKING DRAFT Committee (SAC) and basin and bay area stakeholder committees, “develop “ develop environmental flow analyses and a recommended flow regime” regime” that “maintain(s) “maintain(s) the viability of the state’s streams, rivers, and bay and estuary systems” systems” using “reasonably “reasonably available science.” science.” BBESTs are responsible for flow recommendations required by Senate Bill 3. It is thus within their purview to consider reasonably available scientific methods to account for instream sediment and its delivery to bay and estuary systems. The imminent deadlines for which the BBESTs must  provide flow-regime recommendations recommen dations exclude the possibility of making present-day sedimentload measurements and analyses for the short-term requirements. However, estimates or  predictions of sediment transport for various flows would serve as a benchmark from which to assess programmatic goals, and adaptive management practices could include consideration of sediment data as they become available. Measurable objectives that link sediment to healthy rivers and floodplains include achieving optimized: (1) channel-bed elevations and rates of bank erosion; (2) instream geomorphic unit structure and function, including composition and adjustment frequency of units such as poolriffle sequences, bars, and benches, among others (see Brierley and Fryirs, 2005); (3) turbidity; and (4) floodplain accretion rates. Measureable objectives that link sediment to healthy estuaries include achieving optimized: (1) rates of deltaic accretion, (2) rates of estuarine shoreline erosion, and (3) turbidity. Achieving these objectives would promote healthy aquatic and riparian habitats by supporting the abiotic conditions to which native species have successfully adapted over time.

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WORKING DRAFT

SECTION 4 METHODS OF ASSESSMENT Suspended load and bedload are measured or estimated separately because the physical processes that govern their rates of transport are contingent on different factors. The sum of suspended load and bedload is the total sediment load. Methods to assess suspended load and bedload in Texas rivers and streams can be separated into two categories: (1) historical data analyses and (2) model estimates. 4.1 

HISTORICAL SUSPENDED-SEDIMENT DATA

Historical suspended-sediment load data are available until the early 1980s for various streamflow-gaging stations in Texas, and are derived from two general sources: (1) reports  published by the Texas Water Development Board (TWDB) and predecessor agencies and (2) the U.S. Geological Survey (USGS). Suspended-sediment load measurements commonly are associated with discharge to generate a sediment-discharge rating curve. This, however, is  problematic because suspended-sediment concentrations are known to be variable for a given discharge. Stormflow hydrographs usually, but not always, are characterized by higher suspended-sediment concentrations during the rising limb than the falling limb, referred to as a type-I hysteresis loop (Figure 3). Further, the timing between storm events also influences availability of sediment from the watershed, such that an initial stormflow following relatively dry conditions usually has a greater suspended-sediment concentration than subsequent flows of similar magnitude. Aside from these complications, assessments of suspended-sediment load for various flows are encouraged.

Figure 3. 3. Type-I hysteresis loop of suspended-sediment concentrations for two stormflow events, showing (1) concentrations higher on the rising limb than the falling limb and (2) sediment exhaustion effects for the second, larger flood (from Hudson, 2003).

A series of reports by the TWDB and predecessor agencies (Stout et al., 1961; Adey and Cook, 1964; Cook, 1967; Cook, 1970; Mirabal, 1974; Dougherty, 1979; Quincy, 1988) summarize daily suspended-sediment concentration and load measurements into monthly values at various 6

 

WORKING DRAFT stations in Texas over various periods of record. The data were collected by the “Texas-sampler method”. Historic suspended sediment samples were obtained in an 8-oz narrow-neck bottle held in a 10-lb torpedo-shaped frame, positioned no more than one foot below the water surface. Samples were obtained daily at one-sixth, one-half, and five-sixths of the water-surface width (Stout et al., 1961). To account for increasing suspended sediment concentrations with depth, the measured percent of suspended sediment by weight was multiplied by 1.102 to obtain the mean  percentage of suspended sediment in the vertical profile (Quincy, 1988). The d data ata summarized in these reports were collected to estimate reservoir siltation and should be used with caution for determining an environmental flow regime. The USGS also collected suspended-load data at various stations in Texas and for various  periods of record. Data typically were collected 5 to 10 times per year for various flow magnitudes. The data can be accessed through the National Water Information System (NWIS) at http://waterdata.usgs.gov/tx/nwis/qwdata http://waterdata.usgs.gov/tx/nwis/qwdata.. USGS suspended-sediment data were collected by one of two methods: (1) equal-discharge-increment (EDI) or (2) equal-width-increment (EWI) (Edwards and Glysson, 1999). In simple terms, the EDI method obtains depth-integrated samples of suspended sediment from the centroids of equal-discharge increments across the channel. The EWI method obtains depth-integrated samples of suspended sediment at equally-spaced increments across the channel. Both methods provide similarly accurate results. A comparison of the “Texas-sampler method” and the USGS method was made by Welborn (1967). For sand-bed rivers, including the Sabine, Neches, Trinity, and San Jacinto, correlations could not be formulated between the two methods and preference is given to the more accurate USGS method because of highly-variable ratios of the two estimates along different rivers. However, for rivers with mixed or gravel beds, it was found that suspended-sediment load (in tons/year) computed by the former method closely matches loads computed by the USGS method. Strengths:  representative of historical conditions; measured data; easily coupled with Strengths: representative streamflow measurements  USGS data not available since mid-1990s; TWDB data not available since midWeaknesses: USGS Weaknesses: 1980s; method not as restricted accurate astoUSGS depth-integrated restricted to selectedTexas-sampler streamflow-gaging stations; the measurement periodmethod; of record 4.2 

HISTORICAL BEDLOAD DATA

Historical bedload data for Texas rivers are practically unavailable. Discrete measurements of  bedload probably are available in isolated sources associated with one-time investigations. However, the great difficulties in accurately measuring bedload, especially in sand-bed channels, should be considered if data sources are located. If sufficient historical bedload data are identified and their quality deemed acceptable, then computations of effective discharge for  bedload transport can be made with available streamflow data.  representative of historical conditions; measured data Strengths: representative Strengths:

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WORKING DRAFT Weaknesses:   mostly unavailable, unless embedded within published or unpublished projectWeaknesses:  specific reports; restricted to measurement stations; restricted to the measurement period of record 4.3 

SEDIMENT TRANSPORT MODELS

Bedload models, usually based on hydraulic principles, are notoriously inaccurate (Gomez and Church, 1989), uncertain (Gomez and Phillips, 1999), and applicable to rivers that exhibit steady-state equilibrium, but offer the most rapid approach to estimate transport. The various formulas for estimating bedload transport commonly require values for bed-material particle size, channel slope (energy gradient), flow depth, among other measureable or estimated factors. Common bedload transport equations include Meyer-Peter and Müller (1948), Einstein (1950), Ackers and White (1973), Bagnold (1980), Parker et al. (1982), and Gomez (2006), among others. The choice of bedload equations should be based on: (1) the composition of the bed material, (2) channel geometry, and (3) the hydraulic conditions under consideration. If changes in channel-bed and bank positions over time are known, another approach is Exner’s equation used in a morphodynamic model. The following sources provide useful bedload transport model equations and explanations: (1) Gomez and Church (1989), (2) Stevens and Yang (1989), and (3) Robert (2003). A very useful application to estimate bedload and suspended-load transport is SAM – Hydraulic Design Package for Channels, which includes various sediment transport equations that accompany a one-dimensional hydraulic computation model. User input to SAM includes channel cross-sectional data, energy gradient (channel slope), bed-material particle size distributions, and a roughness value, among other limited data. The SAM application assesses the user input to determine which sediment transport equations are most applicable, and then computes sediment transport loads using a combination of model output with the cross-sectional geometry data. Further, flow-duration curve data can be included to determine which flows cumulatively transport the most sediment over time, referred to as the effective discharge. A final comment should be made that personnel involved with application of sediment transport models or SAM should have considerable background or training, and caution should be given to computed estimates. For some rivers in Texas, a source of data to parameterize sedimenttransport models is provided in a 4-CD set of data published by the National Cooperative Highway Research Program (2004). Further, cross-sectional data from streamflow measurements can be requested from the U.S. Geological Survey (USGS) water-science centers in Texas. Strengths:  not contingent on sediment-load measurements; flexibility over space and time (e.g., Strengths: not model parameters could be from any station along a river, or could be historical) Weaknesses:   result accuracy; requires accurate model parameters (e.g., cross-sectional data, Weaknesses:  channel slope, bed-material size distribution)

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WORKING DRAFT 4.4 

EFFECTIVE DISCHARGE

Sediment load is a measure of mass transport over time and, with a reasonably extensive dataset, one could formulate sediment-flow prescriptions in the same manner as streamflow. However, the most commonly applied method to associate sediment load with streamflow is through an analysis of effective discharge. Effective discharge is the flow that cumulatively transports the majority of sediment at a channel cross section over time (Figure 4). It is usually a flow of moderate magnitude and frequency. Although high-magnitude floods can transport substantial quantities of sediment, their relatively infrequent occurrence often is outpaced by the sediment transport of more frequent moderate flows. Although effective discharge is informative with respect to sediment transport, it offers little guidance in predicting channel form or adjustment over time.

produ ct of the sediment Figure 4. 4. Effective discharge, in its graphical form, is the largest product transport rate and the frequency of transport (from Wolman and Miller, 1960; scanned from Andrews and Nankervis, 1998).

Although a number of investigations confirm that relatively frequent, moderate flows (Hudson and Mossa, 1997) or bankfull flows (Andrews and Nankervis, 1995; Biedenharn et al., 1999; Torizzo and Pitlick, 2004) are responsible for the majority of cumulative sediment transport over time (Figure 5), others have shown that infrequent, high-magnitude floods equate to the effective discharge (Gupta, 1988; Bourke and Pickup, 1999), especially in fluvial systems with highly variable flow regimes. Generally, effective discharge is less frequent as the average annual  precipitation and regularity of flooding decreases. A further complication associated with applications of effective discharge is the tendency to rely solely on one flow value to transport sediment over time. Instead, an emphasis on flow variability and the range of flows necessary to transport sediment over time should be embraced. For example, average flow conditions are known to transport appreciable quantities of sediment in sand-bed river systems.

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WORKING DRAFT

Figure 5. 5. Effective discharge in this example approximately app roximately is equal to the bankfull discharge (from Andrews, 1980; scanned from Knighton, 1998). 199 8).

A process to compute effective discharge at gaged or ungaged stations is provided in Biedenharn et al. (2000). discharge are requires aninto annual flow-duration curve and a sedimentdischarge ratingEffective curve. Discharges divided a range of equal arithmetic classes and the total sediment load is computed for each class. This is done by multiplying the frequency of each flow class by the median sediment load of that class. The average of the flow class with the highest load is the effective discharge. Further, the quantification of sediment load by flow classes enables an assessment of the relative importance of the effective discharge compared to lesser and greater flows. For purposes of instream channel maintenance, the method is suggested for bed-material load only. However, the method could independently be applied to determine effective flows for suspended load or bedload. The actual concept of effective discharge should be taken into consideration when evaluating its  potential to prescribe various channel-maintenance flows. First, its application assumes steadystate equilibrium of the river channel, or the tendency to fluctuate around an average geometric condition (e.g., bankfull width-to-depth ratio) (Figure 6). If the channel does not display equilibrium, such as would be the case for an actively incising channel-bed, then a computation of effective discharge does not describe the condition acceptable for conservation or restoration efforts. Further, the effective discharge is a product of flow frequency; therefore a regulated adjustment of the flow regime would result in a different value.

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WORKING DRAFT

Figure 6. 6. Concepts of equilibrium in fluvial geomorphology (from Schumm, 1977; scanned from Ritter et al., 2002). Channel rehabilitation rehab ilitation or engineering applications focus on graded time scales, and efforts are usually made to promote a steady-state channel condition that is resilient to disturbances (e.g., floods).

Strengths:   adaptable to both measured and model-estimated data; adaptable to bedload, Strengths:  suspended-load, or total load Weaknesses:  assumes steady-state equilibrium; restricted to streamflow-measurement stations; Weaknesses: assumes restricted to the streamflow-measurement period of record

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WORKING DRAFT SECTION 5 RECOMMENDATIONS AND EXAMPLE COMPUTATION OF EFFECTIVE DISCHARGE An analysis of the effective discharge of sediment transport at gaging stations with a sufficient  period of record (20 or more years) could serve as an overlay to modify HEFR-based flow  prescriptions (mostly high-pulse flows or overbank flows). For gaging stations with accurate suspended-load data, effective discharge can be computed using the methodology described in Biedenharn et al. (2000). Bedload transport can be accounted for with a model equation, which requires inputs of bed-material size, channel slope, cross-sectional geometry, and flow depth, among other hydraulically relevant parameters. The caveat of using measured suspended-load data is that the values represent conditions during the period of measurement, which might have  been degraded or not representative rep resentative of desired conditions for many rivers in Texas, especially for stations downstream of reservoirs. It should be recognized that an analysis of effective discharge does not encompass nor entirely explain the breadth of fluvial geomorphic processes. Sediment transport, however, is a fairly straightforward process to relate with streamflow, and collection of sediment-transport data commonly occurs simultaneous with streamflow at a gaging station. 5.1 

EXAMPLE OF EFFECTIVE DISCHARGE ANALYSIS

An illustrative example is provided below for the Brazos River near Richmond, Texas, using streamflow and suspended-load data from the USGS National Water Information System (NWISWeb) (U.S. Geological Survey, 2009) and supporting data from the National Cooperative Highway Research Program (2004). Further, a procedural flowchart of effective discharge analysis is shown in Figure 7. Data required for an analysis of effective discharge at 08114000 Brazos River at Richmond, Texas, are summarized in Table 1.

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Figure 7. 7. Procedural flowchart for recommended computation of effective discharge for suspended-sediment load, bedload, and total load.

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WORKING DRAFT Table 1. Data 1. Data required for effective discharge analysis at 08114000 Brazos River at Richmond, Texas. Data

Source

1.  Daily mean streamflow (ft /s) 2.  Suspended sediment load (tons/day) 3

USGS NWISWeb USGS NWISWeb water-quality data  National Cooperative Cooperative Highway Research Program

3.  Bed-material particle size (in)

(2004) Cooperative  National Cooperative Highway Research Program (2004)  National Cooperative Cooperative Highway Research Program (2004) Hard-copy USGS streamflow measurement notes (available at USGS water science centers)

4.  Dimensionless channel slope 5.  Manning’s n coefficient 6.  Cross-sectional channel geometry data

5.1.1  Flow-Duration Curve 1.  Daily mean streamflow for the period of record were downloaded from USGS NWIS and exported to a spreadsheet. Days with missing values were deleted from the dataset, and streamflow values were sorted in descending order. Intervals of discharge were 3

subdivided into 36 classes, the last class being 100,000 ft /s (Table 1). A simple quantitative method to determine class intervals is provided in Biedenharn et al. (2000),  but was not used for this analysis. Exceedance frequencies were computed using the number of days in the period of record, and plotted data are shown in Figure 8.

Figure 8. 8. Flow-duration curve for 08114000 Brazos River at Richmond, Texas, for the full  period of record using daily mean values. The high density of points at the upper tail is for a more accurate determination of effective discharge.

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WORKING DRAFT 5.1.2  Suspended-Sediment Load 2.  Suspended-sediment-load (SSL) data (period of record: February 1966 to September 1995) (tons/day) were downloaded by selecting the water quality / sediment measurements from USGS NWIS, and were exported to a spreadsheet. Records were sorted by the parameter code, and only data for suspended-sediment load were retained (USGS parameter code 80155). For days with multiple measurements of SSL, the mean value was used for that day. SSL (in log-10 space) for each day was plotted against its corresponding daily mean streamflow (in log-10 space), and a power function was fit to 3 the data (Figure 9). The power function fitted to predict SSL from streamflow (Q (Q) (ft /s) is:

   SSL  = (0.0000527)Q2.1463, where SSL SSL is  is suspended-sediment load (tons/day) and

•

3

Q is discharge (ft /s).

Figure 9. 9. Suspended-sediment-load and streamflow rating curve for 08114000 Brazos River at Richmond, Texas. Scatter about the power trendline is attributed to sediment availability and hysteretic behavior of suspended-sediment concentrations over time. 3.  A representative streamflow for each discharge class interval was computed as the mean discharge between two classes. The representative discharge was used in the power function determined in step #2 to compute SSL in tons/day for each discharge class. The result was multiplied by the discharge exceedance frequency to obtain the load

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WORKING DRAFT transported by each discharge class. Finally, the load values were plotted as a histogram for each class, using the discharge value originally used in the flow-duration curve (Figure 10). Results of the entire analysis are also presented in Table 2. It takes some iterations of this step to ensure that discharge class intervals are appropriate to accurately determine the effective discharge. 4.  The effective discharge is determined by evaluating the modal class of the histogram. In this case, four discharge classes exhibited the highest suspended-sediment loads, and the 3 mean discharge representing their bounds was selected and approximates 46,000 ft /s, which is the effective discharge for suspended-sediment transport. Thus, for the period February 1966 to September 1995, the Brazos River at Richmond transported the 3 cumulative majority of suspended sediment at about 46,000 ft /s. However, this does not include bedload transport. According to the National Weather Service (NWS) West Gulf River Forecast Center (http://www.srh.noaa.gov/wgrfc/ (http://www.srh.noaa.gov/wgrfc/), flood stage occurs at a USGS 3 stage of 48 feet, or 81,800 ft /s based on the current expanded stage-discharge rating table. Therefore, effective discharge of SSL is substantially less than flood stage.

Figure 10. 10. Suspended-sediment load (SSL) histogram showing effective discharge for SSL at 3 08114000 Brazos River at Richmond, Texas, approximately is 46,000 ft /s.

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WORKING DRAFT Table 2. Computations 2. Computations for the flow-duration curve and histogram for determination of effective discharge for suspended-sediment load (SSL). Gray columns were used to generate an SSL histogram. (ft3/s; cubic feet per second; %, percent; SSL, suspended-sedim suspended-sediment ent load) Streamflow (ft3 /s) 0 100 500 1,000 1,500 2,000 3,000 4,000 5,000 10,000 12,500 15,000 17,500 20,000 22,500 25,000 27,500 30,000 32,500 35,000 37,500 40,000 42,500 45,000 47,500 50,000 52,500 55,000 57,500 60,000

Days exceeded 32,796 32,774 31,669 27,009 22,838 19,809 16,177 13,908 12,066 6,987 5,624 4,489 3,700 3,100 2,615 2,234 1,956 1,699 1,476 1,303 1,166 1,037 941 824 731 657 575 519 462 402

Exceedance frequency 100.00% 99.93% 96.56% 82.35% 69.64% 60.40% 49.33% 42.41% 36.79% 21.30% 17. 17.15% 15% 13. 13.69% 69% 11. 11.28% 28% 9 9.45% .45% 7.97% 6.81% 5.96% 5.18% 4.50% 3.97% 3.56% 3.16% 2.87% 2.51% 2.23% 2.00% 1.75% 1.58% 1.41% 1.23%

Representative streamflow (ft3 /s) 0 50 300 750 1,250 1,750 2,500 3,500 4,500 7,500 11,250 13,750 16,250 18,750 21,250 23,750 26,250 28,750 31,250 33,750 36,250 38,750 41,250 43,750 46,250 48,750 51,250 53,750 56,250 58,750

SSL (tons per day) via power function 0 0 11 78 234 481 1,035 2,130 3,653 10,936 26,110 40,165 57,486 78,154 102,240 129,807 160,912 195,607 233,941 275,959 321,702 371,209 424,517 481,661 542,675 607,590 676,436 749,242 826,035 906,843

SSL (tons) 0 0 11 64 163 291 510 903 1,344 2,330 4,477 5,498 6,486 7,387 8,152 8,842 9,597 10,133 10,529 10,964 11,437 11,738 12,180 12,102 12,096 12,172 11,860 11,857 11,636 11,116

62,500 65,000 67,500 70,000 75,000 100,000

348 287 245 205 143 18

1.06% 0.88% 0.75% 0.63% 0.44% 0.05%

61,250 63,750 66,250 68,750 72,500 87,500

991,691 1,080,604 1,173,605 1,270,718 1,424,145 2,132,271

10,523 9,456 8,767 7,943 6,210 1,170

5.1.3  Cross-Sectional Data 5.  In order to apply a bedload transport model, cross-sectional data are required to  parameterize various steps in the model development. The choice of a cross section is very important because it represents the condition of the channel at a given time and  place, such that the choice of an incised, degraded cross section downstream of a reservoir would provide results inappropriate for assessment of naturalized conditions.

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WORKING DRAFT For this exercise, hard-copy USGS streamflow measurement notes for two measurements in February 1998 (moderate flow) and November 2004 (high flow) were used to construct a cross-section on the upstream side of the bridge at Richmond. The moderate flow in 1998 was used to construct the channel bed and base of the bank, and the 2004 flow was used to vertically extend the banks to a maximum stage of 33.8 feet. Based on the observed bank angle, banks were artificially extended to the NWS flood stage of 48 feet (Figure 11) The reason for using a composite of two flows was to avoid excessive  bed scour during the high flow but, nonetheless, capture as much of the bank morphology as possible.

Figure 11. 11. Cross section of 08114000 Brazos River at Richmond, Texas, based on USGS streamflow measurements in February 1998 and November 2004, and extended to NWS flood stage of 48 feet. The moderate flow of 1998 was used to construct geometry up to about 18 feet and the high flow of 2004 further extended geometry to about 34 feet. 6.  The cross section was imported into WinXSPRO, a free software package available online from the U.S. Department of Agriculture Forest Service (2009). Care should be taken to correctly associate WinXSPRO results with the appropriate USGS stage because the software automatically sets the lowest point in the section to “0”. Hydraulic values, including hydraulic radius and mean velocity, for 0.25-ft stage increments were computed using the following hydraulic data for the Brazos River at Richmond, Texas, from the National Cooperative Highway Research Program (2004) CD set: Dimensionless channel slope: 0.00012 Manning’s n: 0.03

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WORKING DRAFT 5.1.4  Bagnold’s (1977) Bedload Model 7.  For all discharge class intervals used to compute suspended-sediment load above, a series of computations were made to estimate bedload transport (Table 3). English units were used. First, mean velocity (U  (U ) (ft/s) and hydraulic radius ( R)  R) (ft) for each discharge were 3 entered from the WinXSPRO results. Stream power per unit area ( ω) (lb/s ) for each discharge class interval was computed from the following equation:

 

•

3

ω  =  ρ gdSU ,

where  ρ is the mass density of water (62.28 lb/ft ), ), g   g  is   is acceleration 2 due to gravity (32.17 ft/s ), d   is mean flow depth (ft) which is considered analogous to  R  R,, S   is dimensionless channel slope (0.00012), and U   is mean velocity (ft/s).

Using the median particle size ( D  D50) (ft) of bed-material for the Brazos River at Richmond from the National Cooperative Highway Research Program (2004) CD set (see 2  below), the critical shear stress (τ c) (lb/ft ) for entrainment was computed from the following equation:

 

•

τ c  = τ *  D50, *(( ρs- ρ) D

where τ * *is is the dimensionless Shields parameter (0.03 for sand3

 bed channels),  ρs  is the mass density of sediment (164.98 lb/ft   for quartz), and  D50 is the median particle size (0.00075 ft). Average Bed Material D Material  D16,  D50,  D84 (in) (or the diameter at which 16, 50, and 84 percent of the sediment is finer than): 0.006, 0.009, 0.013  Next, the mean flow depth (ft) required to entrain the median particle size ( D  D50) (ft) was computed from the following equation:

  d  =  = τ c /(  ρ S )

•

From this value, Manning’s equation was used to compute the critical flow velocity ( U c) (ft/s) required to entrain the median particle size ( D50) (ft):

  U c = (1.49d 2/3 S 1/2)/ n, where n is Manning’s coefficient (0.03).

•

3

 Next, the critical stream power (ωc) (lb/s ) required to entrain the median particle size (  D D50) (ft) was computed from the following equation:

 

•

ωc =

U cτ c 

The Bagnold (1977) formula to estimate the bedload transport rate ( I  b) (lb/ft/s) for each discharge class interval was computed from the following equation:

   I b = ( ω- ωc)3/2(d  /  D50)-2/3 

•

19

 

WORKING DRAFT Finally, the bedload transport rate ( I   I  b) (lb/ft/s) was multiplied by the wetted perimeter (from WinXSPRO) for each discharge class interval to estimate a channel-wide bedload transport rate (lb/s), and the value was converted to tons/year.

Bagn old (1977) model and effective Table 3. Computations 3. Computations for bedload transport using the Bagnold 3 discharge for bedload. Critical stream power ( ωc) was computed to be 0.00057 lb/s  for this example. Gray columns were used to generate a bedload histogram. (ft3/s; cubic feet per second; %, percent; ft, feet; ft/s, feet per second;  pounds per cubic second; second; lb/ft/s, pounds per foot per second; yr, year year))

, stream power per unit bed area; lb/s 3,

ω

7.8 8.87 9.75 10.45 11.06 12.11 13.02 13.89 17.66 19.24 20.78 22.26 23.68 25.01 26.31 27.56 28.76 29.94 31.08 32.2 33.28 34.35

Mean velocity (ft/s) 2.1 2.3 2.4 2.5 2.5 2.7 2.8 2.9 3.3 3.5 3.7 3.8 4.0 4.1 4.2 4.4 4.5 4.6 4.7 4.8 4.9 4.9

Mean depth (ft) 7.6 8.4 9.1 9.7 10.1 10.9 11.6 12.2 14.9 16.2 17.5 18.7 19.9 20.9 21.8 22.7 23.5 24.4 25.2 25.9 26.6 27.4

Stream power (ω) (lb/s3) 3.837 4.645 5.251 5.830 6.071 7.076 7.809 8.506 11.822 13.632 15.568 17.085 19.138 20.602 22.013 24.014 25.425 26.985 28.476 29.890 31.337 32.280

Bedload transport (lb/ft/s) 0.01605 0.02000 0.02278 0.02555 0.02642 0.03160 0.03515 0.03864 0.05541 0.06489 0.07522 0.08274 0.09411 0.10173 0.10925 0.12116 0.12899 0.13755 0.14593 0.15409 0.16250 0.16657

Bedload transport (tons/yr) 62,039 79,191 92,393 105,209 110,481 135,127 153,075 171,324 264,034 315,365 370,302 412,541 473,693 518,490 565,418 636,631 685,881 737,935 796,713 850,992 907,706 940,913

35.38 36.4 37.42 38.4 39.36 40.28 41.12 41.95 42.78 43.58 44.38

5.0 5.1 5.2 5.2 5.3 5.4 5.4 5.5 5.6 5.6 5.7

28.0 28.7 29.3 30.0 30.6 31.2 31.7 32.2 32.7 33.2 33.7

33.660 35.191 36.631 37.506 38.992 40.507 41.156 42.579 44.027 44.700 46.183

0.17482 0.18383 0.19256 0.19638 0.20544 0.21473 0.21759 0.22660 0.23582 0.23882 0.24832

998,564 1,061,660 1,118,126 1,155,837 1,222,095 1,287,515 1,318,420 1,383,729 1,451,174 1,480,947 1,551,610

Streamflow (ft3 /s)

Exceedance frequency

Stage (ft)

100 500 1,000 1,500 2,000 3,000 4,000 5,000 10,000 12,500 15,000 17,500 20,000 22,500 25,000 27,500 30,000 32,500 35,000 37,500 40,000 42,500

99.93% 96.56% 82.35% 69.64% 60.40% 49.33% 42.41% 36.79% 21.30% 17.15% 13.69% 11.28% 9.45% 7.97% 6.81% 5.96% 5.18% 4.50% 3.97% 3.56% 3.16% 2.87%

45,000 47,500 50,000 52,500 55,000 57,500 60,000 62,500 65,000 67,500 70,000

2.51% 2.23% 2.00% 1.75% 1.58% 1.41% 1.23% 1.06% 0.88% 0.75% 0.63%

Bedload (tons)

61,998 76,470 76,090 73,264 66,731 66,653 64,916 63,032 56,251 54,080 50,686 46,542 44,775 41,342 38,515 37,970 35,532 33,211 31,654 30,255 28,701 26,997 25,089 23,664 22,399 20,265 19,340 18,137 16,161 14,683 12,699 11,063 9,699

8.  A bedload histogram was plotted in the exact same manner as the suspended-load exercise 12), multiplying theit final bedload The (tons/year) thethat exceedance frequency(Figure of the discharge for which was modeled. results by show effective

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WORKING DRAFT discharge for cumulative bedload transport occurs at relatively low flows. This, however, is an inaccurate assessment of bedload transport in reality. The Bagnold (1977) model is dependent on excess stream power, which is generated to a large measure by depth and velocity. The flaw in this example occurred because the stage for very low flows 3 according to the USGS, say 100 ft /s, filled up the cross section to a mean depth of 7.6 feet at a mean velocity of 2.1 ft/s according to hydraulic computations modeled in WinXSPRO. These modeled hydraulic conditions are more than adequate at transporting sand-sized bedload, and their almost constant occurrence over time ensured low flows outpaced moderate to high flows with respect to cumulative transport. In reality, the 3 hydraulic conditions at 100 ft /s at this cross section are sluggish and pond-like, not capable of transporting sand-sized bedload. Furthermore, it is very unusual for bedload to exceed suspended-load transport, thereby providing additional evidence for the  problematic data used to compute bedload. This example underscores the importance of selecting an appropriate cross section to model bedload transport using any given equation. For appropriate cross sections with adequate data, however, the Bagnold (1977) equation has worked well for other investigations.

ina ccurately low estimate of effective discharge for Figure 12. 12. Bedload histogram showing an inaccurately  bedload at 08114000 Brazos River at Richmond, Texas. 9.  Finally, the practitioner can combine suspended load (tons) and bedload (tons) for a given flow to evaluate the effective discharge for total sediment load.

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WORKING DRAFT 5.2 

ADVOCACY OF THE SAM HYDRAULC DESIGN MODEL

The SAM hydraulic design model efficiently computes the exercises shown above when  parameterized with sufficient data. Furthermore, SAM can recommend appropriate sediment transport formulae for the given input, such as channel slope and bed-material particle size. The use of the SAM hydraulic design model is a tool that can be used to establish effective discharge at gaging stations, but should be done by an expert in the field of fluvial geomorphology or sediment transport dynamics. As discussed above, effective discharge should be applied with caution for rivers that do not exhibit steady-state equilibrium. The SAM model requires cross-sectional geometry data for the location of interest. For rivers that are degraded, such as those that have incised immediately  below reservoirs, cross-sectional channel geometry probably is not representative of any natural condition. As a hypothetical example, cross-sectional area of a river channel immediately downstream of a reservoir is greatly enlarged as a result of channel incision and bank retreat, and SAM computes a sediment load much greater for the enlarged channel than would be expected naturally. Because the sediment transport models embedded within SAM are based on equilibrium-based theoretical constructs, however, the output of the model provides the analyst with a reference condition of sediment transport. As such, SAM output can be used in conjunction with field measurements of suspended load and bedload to determine if the river is over- or under-achieving with respect to sediment transport. Regardless of the analysis employed, values of effective discharge should be considered with respect to desired conditions of particular river systems. For some rivers, it might be desirable to transport less sediment load than that computed by an effective discharge analysis. As a hypothetical example, a river reach 25 miles downstream of a reservoir receives much less sediment than it did during pre-impoundment conditions. In order to prevent channel incision and associated bank failure over time, it would be desirable for sediment transport to underperform that predicted by a SAM analysis of steady-state conditions. Another serious concern related to the practicality of effective discharge for environmental flow programs is the stasis of its approach. If an existing flow regime is modified to satisfy a prescription, then it is likely that the magnitude and frequency of the effective discharge changes as well. Iterations of effective overlays and subsequent modification of the flow regime becomes impracticaldischarge at some level.

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WORKING DRAFT

SECTION 6 DECISION POINTS Similar to the HEFR-based approach to determine an environmental flow regime for Texas rivers, a variety of decisions are required to compute the effective discharges of sediment transport processes. One decision point not specifically discussed below regards computation of effective discharges for ungaged locations, which is beyond the scope of this report. The decision  points include: 1.  Bedload, suspended load, or total sediment load:  load:   The practitioner must decide if effective discharge will be required for bedload only, suspended load only, or the combination of both (total load). For objectives associated with instream-habitat structure, channel morphology, deltaic lateral accretion, and beach or shoreline maintenance, bedload is the most important sedimentary variable. For objectives associated with floodplain sedimentation, turbidity, or deltaic vertical accretion, suspended-load is the most important sedimentary variable. Finally, total load constitutes the most complete picture of sediment transport.  transport.   2.  Historically collected sediment-load data or model application: The application: The practitioner must decide whether to use previously collected sediment-load data or to apply a sedimenttransport model equation to estimate load. In Texas, the USGS and TWDB have historically collected suspended-load data at a number of USGS streamflow-gaging stations. Bedload, however, has not historically been collected, unless done so on a  project-specific basis. b asis. It is highly likely, therefore, that tha t a model equation would have to  be used for computation of effective discharge for bedload transport.  transport.  3.  USGS or Texas-sampler method for historical suspended-load data: The data: The USGS has historically collected depth-integrated suspended-load data at a number of streamflowgaging stations in Texas prior to the mid-1990s. The TWDB has various published reports of historical suspended-load data obtained by the Texas-sampler method at selected streamflow-gaging stations prior to the mid-1980s. In general, USGS depthintegrated data are more accurate than the Texas-sampler method.  method.  4.  Period of record: The record: The period of record is a twofold decision: (a) hydrologic data and (b) sediment-load data. The period of record for sediment-load data is not applicable if a sediment-transport model equation is used.  used.  a.  Historical streamflow data are required to generate a flow-duration curve for computation of effective discharge. The choice of an appropriate period of record of streamflow data could reflect pre- or post-regulation conditions, among other historical changes to the river’s flow regime.  regime.  b.  Sediment load is highly sensitive variable over space and time. Sediment concentrations in the water column are dependent on season, antecedent rainfall,

23

 

WORKING DRAFT land-use, characteristics of the storm hydrograph, and upstream impoundments, among other variables. The period of record for measured sediment-load sediment-load data could reflect pre- or post-regulation conditions, among other historical changes to the river’s sediment-transport regime.  regime.  5.  Flow-duration class intervals:  intervals:  A flow-duration curve requires the practitioner to establish “class intervals” which are related to exceedance frequency of that interval’s representative flow. Although various published sources offer guidance on establishing class intervals, the choice is relegated to the practitioner. Accuracy of effective discharge increases if class intervals are shorter and more numerous (e.g., class intervals of 1,000 3 3 ft /s are more accurate than 5,000 ft /s). /s).   6.  Sediment-transport model:  model:  This decision is only required if the practitioner does not have or chooses not to use measured sediment-load data to determine effective discharge. A variety of model equations exist that estimate bedload transport rates for various flow conditions, and are based on measured or estimated parameters. Bedload equations commonly are suited to particular conditions, such as a low-gradient sand-bed channel, for example. Other model equations exist that estimate suspended-load transport rates using either measured or estimated parameters. The choice of an appropriate model equation is relegated to the practitioner, possibly with guidance from the SAM hydraulic design model.  model.  7.  Channel cross-section dimensions:  dimensions:  This decision is only required if using a model equation to estimate sediment load. Cross-sectional data are needed to compute channel hydraulics (e.g., width, mean depth, mean velocity) based on a given slope and flowresistance coefficient. Further, most model equations render sediment-load estimates for a given channel length, and require a wetted perimeter for extrapolation to channel-wide transport rates. As shown from the Brazos River at Richmond, Texas, example above, an unrepresentative cross section can lead to erroneous results. Cross-sectional dimensions could be chosen to represent pre- or post-regulation conditions, pre- or post-disturbance conditions, straight-reach or meander-bend conditions, among other complex arrangements of channel shape over space and time.  time.  8.  Model parameters: This parameters: This decision is only required if using a model equation to estimate sediment load. Various parameters, including channel slope, particle size, mean depth, and water temperature, among others, are needed to parameterize sediment-transport model equations and compute selected hydraulics at a channel cross section. Various  published and unpublished sources exist that provide this information. For certain applications, the practitioner could elect to estimate e stimate required parameters. parameters.   9.  Extrapolation of effective discharge to a channel reach:  reach:  As outlined above, computation of effective discharge is restricted to one channel cross section. Given this

24

 

WORKING DRAFT restriction, environmental flow objectives associated with sediment transport are valid for one station. If desired, extrapolation to a channel reach should consider variability in sediment sources and sinks upstream and downstream of the station, including tributary inputs, distributary outputs, active bank erosion, channel incision or aggradation, overbank deposition, among other complex watershed and channel characteristics and  processes.    processes.

25

 

WORKING DRAFT SECTION 7 CONCLUSIONS An analysis of effective discharge of suspended-sediment load (SSL), bedload, and/or total load at streamflow-gaging stations could be used to modify HEFR-based flow prescriptions for establishing environmental flows. For the majority of locations, the high-pulse flow or overbankflow categories are associated with the cumulative majority of sediment transport over time. Computations for suspended load should utilize historical measurements, if available, and  bedload likely requires application a pplication of a model equation. Sediment transport, although a lthough relatively straightforward in its association with discharge, does not encompass the breadth of fluvial geomorphic processes. Furthermore, concepts of steady-state equilibrium challenge assumptions that a constant discharge value is responsible for the cumulative majority of sediment transport over time. Finally, practitioners utilizing effective discharge for rivers in Texas should be cognizant of the contemporary sediment-transport regime and historical channel adjustments at each location considered. Assignment of an effective discharge to altered or regulated rivers is  problematic and implementation efforts could be harmful if a holistic perspective (e.g., sediment trapped behind reservoirs, non-representative cross section to estimate bedload transport, etc.) is not considered.

26

 

WORKING DRAFT SECTION 8 REFERENCES Ackers, P., and White, W.R., 1973, Sediment transport—New approach and analysis: ASCE Journal of the Hydraulics Division, v. 99(HY11), p. 2,041–2,060. Adey, E.A., and Cook, H.M., 1964, Suspended-sediment load of Texas streams—Compilation report—October 1959–September 1961: Texas Water Commission Bulletin 6410, 50 p. Andrews, E.D., 1980, Effective and bankfull discharges of streams in the Yampa River Basin, Colorado and Wyoming: Journal of Hydrology, v. 46, p. 311–330. Andrews, E.D., and Nankervis, J.M.,1995, Effective discharge and the design of channel maintenance flows for gravel-bed rivers, in Costa, in Costa, J.E., Miller, A.J., Potter, K.W., and Wilcock, P.R., eds., Natural and anthropogenic influences in fluvial geomorphology: Washington, D.C., American Geophysical Union, p. 151–164. Bagnold, R.A., 1977, Bed load transport by natural rivers: Water Resources Research, v. 13, p. 303–312. Bagnold, R.A., 1980, An empirical correlation of bedload transport rates in flumes and natural rivers: Proceedings of the Royal Society of London, v. 372A, p. 453–473. Biedenharn, D.S., Copeland, R.R., Thorne, C.R., Soar, P.J., Hey, R.D., and Watson, C.C., 2000, Effective discharge calculation—A practical guide: United States Army Corps of Engineers ERDC/CHL TR-00-15, 63 p. Biedenharn, D.S., Little, C.D., and Thorne, C.R., 1999, Magnitude-frequency analysis of sediment transport in the Lower Mississippi River: Vicksburg, Miss., U.S. Army Corps of Engineers, Miscellaneous Paper CHL–99–2. Bourke, M.C., and Pickup, G., 1999, Fluvial form variability in arid central Australia, in in Miller,  Miller, A.J., and Gupta, A., eds., ed s., Varieties of fluvial form: Chichester, UK, Wiley, p. 249–271. Brierley, G.J., and Fryirs, K.A., 2005, Geomorphology and river management—Applications of the River Styles Framework: Malden, Mass., Blackwell, 398 p. Cook, H.M., 1967, Suspended-sediment Suspen ded-sediment load of Texas streams—Compilation report—October 1961–September 1963: Texas Water Development Board Report 45, 62 p. Cook, H.M., 1970, Suspended-sediment Suspen ded-sediment load of Texas streams—Compilation report—October 1963–September 1965: Texas Water Development Board Report 106, 63 p. Dougherty, J.P., 1979, Suspended-sediment load of Texas streams—Compilation report—  October 1971–September 1975: Texas Water Development Board Report 233, 83 p.

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WORKING DRAFT Edwards, T.K., and Glysson, G.D., 1999, Field methods for measurement of fluvial sediment: U.S. Geological Survey Techniques of Water-Resources Investigations, Book 3, Chapter C2, 89 p. Einstein, H.A., 1950, The bedload be dload function for sediment transportation in open chan channel nel flows: U.S. Department of Agriculture Technical Bulletin 1026. Gomez, B., 2006, The potential rate of bed-load transport: Proceedings of the National Academy of Sciences, v. 103, p. 17,170–17,173. Gomez, B., and Church, M., 1989, An assessment of bed load sediment transport formulae for gravel bed rivers: Water Resources Research, v. 25, p. 1,161–1,186. Gomez, B., and Phillips, J.D., 1999, 1999 , Deterministic uncertainty in bed load transport: Journal of Hydraulic Engineering, v. 125, p. 305–308. Gupta, A., 1988, Large floods as geomorphic events in the humid tropics, in in Baker,  Baker, V.R., Kochel, R.C., and Patton, P.C., eds., Flood geomorphology: Chichester, UK, Wiley, p. 301–315. Hudson, P.F., 2003, Event sequence and sediment exhaustion in the lower Pánuco basin, Mexico: Catena, v. 52, p. 57–76. Hudson, P.F., and Mossa, J., 1997, Suspended sediment transport effectiveness of three, large impounded rivers, U.S. Gulf Coastal Plain: Environmental Geology, v. 32, p. 263–273. Knighton, D., 1998, Fluvial forms and processes—A new perspective: London, Arnold, 383 p. Kondolf, G.M., 1994, Geomorphic and environmental effects of instream gravel mining: Landscape and Urban Planning, v. 28, p. 225–243. McKnight, T.L., and Hess, D., 2000, Physical geography—A landscape appreciation, 6th ed.: Upper Saddle River, N.J., Prentice Hall, 604 p. Meyer-Peter, R., and Müller, R., 1948, Formulas for bedload transport, in in Proceedings  Proceedings 2nd  Meeting International Association of Hydraulic Research: Stockholm, p. 39–64. Mirabal, J., 1974, Suspended-sediment load of Texas streams—Compilation report—October 1965–September 1971: Texas Water Development Board Report 184, 121 p.  National Cooperative Highway Research Program, 2004, Archived river meander bend database: Washington, D.C., Transportation Research Board of the National Academies, 4 CD-set.  National Research Council of the National Academies, 2005, The science of instream flows—A review of the Texas Instream Flow Program: Washington, The National Academies Press, 149 p.

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WORKING DRAFT Parker, G., Klingeman, P.C., and McLean, D.G., 1982, Bedload and size distribution in paved gravel-bed streams: ASCE Journal of the Hydraulics Division, v. 108(HY4), 10 8(HY4), p. 544–571. Quincy, R.M., 1988, Suspended sediment load of Texas streams—Compilation report, October 1975–September 1982: Texas Water Development Board Report 306, 153 p. Ritter, D.F., Kochel, R.C., and Miller, J.R., 2002, Process geomorphology, 4th ed.: New York, McGraw-Hill, 560 p. Robert, A., 2003, River processes—An introduction to fluvial dynamics: London, Arnold, 214 p. Schumm, S.A., 1977, The fluvial system: New York, John Wiley, 338 p. Senate Bill 3 Science Advisory Committee for Environmental Flows, 2009, DRAFT—Use of hydrologic data in the development d evelopment of instream flow recommendations for the environmental flows allocation process and the hydrology-based environmental flow regime (HEFR) methodology: SAC-2009-01, 46 p. Stout, I.M., Bentz, L.C., and Ingram, H.W., 1961, Silt load of Texas streams—A compilation report—June 1889–September 1959: Texas Board of Water Engineers Bulletin 6108, 237  p. Texas Commission on Environmental Quality, Texas Parks Pa rks and Wildlife Department, and Texas Water Development Board, 2008, Texas Instream Flow Studies—Technical Overview: Texas Water Development Board Report 369, 137 p. Torizzo, M., and Pitlick, J., 2004, Magnitude-frequency of bed load transport in mountain streams in Colorado: Journal of Hydrology, v. 290, p. 137–151. U.S. Department of Agriculture Forest Service, 2009, 200 9, WinXSPRO version 3.0: at http://www.stream.fs.fed.us/publications/winxspro.html   U.S. Geological Survey, 2009, National Water Information System (NWIS), accessed January 2009, at http://waterdata.usgs.gov/nwis http://waterdata.usgs.gov/nwis   Welborn, C.T., 1967, Comparative results of sediment transport sampling with the Texas sampler and the depth-integrated samplers and specific weight of fluvial sediment deposits in Texas: Texas Water Development Board Report 36. Wolman, M.G., and Miller, J.P., 1960, Magnitude and frequency of forces in geomorphic  processes: Journal of Geology, v. 68, p. 54–74.

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WORKING DRAFT SECTION 9 GLOSSARY channell bed by traction Bedload: a measure of the transport of fluvial sediment along or near the channe Bedload: a or saltation mechanisms; either sand, gravel, or larger size; expressed as mass over time Bed-material load: a load: a measure of the transport of fluvial sediment as bedload or sand grains in suspension during turbulent flows; only comprised of particles derived from the channel  bed; does not include silt or clay particles; expressed as mass over time  time  Effective discharge: the discharge: the flow rate responsible for the majority of cumulative sediment transport over time; usually equated to a relatively frequent, moderate flow event; commonly accepted as bankfull discharge; association with bankfull discharge is less apparent for fluvial systems with a highly-variable flow regime Saltation: a Saltation:  a mechanism of bedload transport where particles skip along the channel bed Sediment budget: a budget: a technique that accounts ac counts for sources (additions) and sinks (subtractions) of fluvial sediment in a defined system (e.g., watershed); accounts for sources from hillslopes, channel banks, tributaries, among others; accounts for removals from impoundments, floodplain storage, distributaries, among others Steady-state equilibrium: concept equilibrium: concept that a river channel adjusts over graded time (decades to hundreds of years) to efficiently convey the amount of discharge and sediment load by maintaining a particular slope, pattern, and shape; suggests that the fluvial system will gradually recover from the effects of a disturbance to the system (e.g., 100-year flood); a fundamental, but controversial, fluvial geomorphic concept Stream power: the power: the product of average shear stress and average velocity; commonly used to  predict sediment transport; expressed in SI units as watts/square watts/square meter   Suspended-sediment load: a load: a measure of the transport of fluvial sediment continuously entrained in the water column; co lumn; mostly clay and silt, with varying amounts of sand derived from the channel bed during turbulent flows; expressed as mass over time Suspended-sediment concentration: the concentration: the concentration of suspended sediment in the water column; computed as the ratio of suspended-sediment load to the streamflow; expressed as milligrams per liter  a mechanism of bedload transport where particles roll or slide along the channel bed Traction: a Traction:  a measure of the transport of fluvial sediment and other material continuously Wash load: load: a entrained in the water column (e.g., clay, silt, and organic matter); does not include the sand-sized fraction; expressed as mass over time

30

 

WORKING DRAFT

SECTION 10 CONTRIBUTORS

Contributor and Contact Information

Franklin Heitmuller, [email protected]  [email protected]  Commentor and Contact Information

TWDB: Greg Malstaff, [email protected] [email protected]  

31