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National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 1 The Gravel River Bankfull Discharge Estimator.

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Presentation on theme: "National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 1 The Gravel River Bankfull Discharge Estimator."— Presentation transcript:

1 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 1 The Gravel River Bankfull Discharge Estimator Gary Parker, 10/2004 A tool from the NCED Stream Restoration Toolbox:

2 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 2 The Stream Restoration Toolbox The Stream Restoration Toolbox consists of current basic research cast into the form of tools that can be used by practitioners. The details of a tool are presented through a PowerPoint presentation, augmented by embedded Excel spreadsheets or other commonly available applications. The toolbox is a vehicle for bringing research findings into practice. While many tools are being developed by NCED Researchers, the opportunity to contribute a tool to the Toolbox is open to the community. For more information on how to contribute please contact Jeff Marr at

3 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 3 Statement of liability and usage This tool is provided free of charge. Use this tool at your own risk. In offering this tool, the following entities and persons do not accept any responsibility or liability for the tool’s use by third parties: The National Center for Earth-surface Dynamics; The universities and institutions associated with the National Center for Earth-surface dynamics; and The authors of this tool. Users of this tool assume all responsibility for the tool results and application thereof. The readers of the information provided by the Web site assume all risks from using the information provided herein. None of the above-mentioned entities and persons assume liability or responsibility for damage or injury to persons or property arising from any use of the tool, information, ideas or instruction contained in the information provided to you.

4 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 4 Title Page Tool Title: The Gravel River Bankfull Discharge Estimator Tool Author: Gary Parker Author Version: 2.0 Associated files: 1) BankfullDischargeEstimator_v2.ppt 2) ToolboxGravelBankfullData.xls Date: October 2006

5 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 5 Introduction This Tool is for Gravel-Bed Streams This Tool Addresses Single-Thread Rather Than Multiple-Thread Rivers This Tool Addresses Mobile-Bed Rather Than Threshold Channels Bankfull Parameters Bankfull discharge Bankfull channel width Bankfull channel depth Channel slope Surface median size The Tool Data Base Range of Parameters Tool Description Implementation Accuracy Appendix: Sediment Size Distributions In Gravel-Bed Streams References Outline of this Document

6 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 6 CAVEAT This tool is provided free of charge. Use this tool at your own risk. In offering this tool, none of the following accept responsibility or liability for its use by third parties: the National Center for Earth-surface Dynamics; any of the universities and institutions associated with the National Center for Earth-surface Dynamics; or any of the authors of this tool.

7 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 7 The Gravel River Bankfull Discharge Estimator This tool consists of an equation to estimate bankfull discharge in an undisturbed (reference) reach of a single-thread, mobile-bed gravel-bed stream from measured channel characteristics. River bankfull discharge is a key parameter for estimating channel geometry. A knowledge of bankfull discharge is necessary for the evaluation and implementation of many river restoration projects. The best way to measure bankfull discharge is from a stage-discharge relation. Bankfull discharge is often estimated in terms of a flood of a given recurrence frequency (e.g. 2-year flood, or a flood with a peak flow that has a 50% probability of occurring in a given year; Williams, 1978). In some cases, however, the information necessary to estimate bankfull discharge from a stage-discharge relation or from flood hydrology may not be available. The tool presented here provides an alternative estimator.

8 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 8 RIVERS ARE THE AUTHORS OF THEIR OWN GEOMETRY Given enough time, rivers construct their own channels. A river channel is characterized in terms of its bankfull geometry. Bankfull geometry is defined in terms of river width and average depth at bankfull discharge. Bankfull discharge is the flow discharge when the river is just about to spill onto its floodplain. A river restoration scheme is likely to become more successful in a shorter amount of time if it takes into account the natural bankfull geometry of a channel. This tool allows estimation of bankfull discharge of a single- thread gravel-bed river with a definable floodplain that actively moves the gravel on its bed from time to time. Bankfull discharge is estimated from measured bankfull channel characteristics.

9 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 9 THIS TOOL IS FOR GRAVEL-BED STREAMS Raging River, Washington, USA: a gravel-bed river Little Wekiva River, Florida, USA: a sand- bed river. This tool addresses gravel-bed streams. Typical gravel-bed streams have bed surface median sizes D s50 in the range from 8 to 256 mm. Boulder-bed streams have median sizes in excess of 256 mm. Sand- bed streams have median sizes between and 2 mm.

10 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 10 THIS TOOL ADDRESSES SINGLE-THREAD RATHER THAN MULTIPLE-THREAD RIVERS Raging River, Washington, USA: a single-thread gravel-bed river Sunwapta River, Canada: a multiple-thread (braided) gravel-bed river This tool addresses single-thread streams. A single-thread stream has a single definable channel, although mid-channel bars may be present. A multiple-thread, or braided stream has several channels that intertwine back and forth.

11 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 11 THIS TOOL ADDRESSES MOBILE-BED RATHER THAN THRESHOLD CHANNELS Raging River, Washington, USA: a mobile-bed river Trinity Dam on the Trinity River, California, USA. A threshold channel forms immediately downstream. This tool addresses mobile-bed gravel streams. Such streams are competent to modify their beds because they mobilize all or nearly all gravel sizes on the bed from time to time during floods. Threshold channels are defined in the next slide.

12 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 12 THRESHOLD CHANNELS Trinity Dam on the Trinity River, California, USA. A threshold channel forms immediately downstream. Threshold gravel-bed channels are channels which are barely not able to move the gravel on their beds, even during high flows. These channels form e.g. immediately downstream of dams, where their sediment supply is cut off. They also often form in urban settings, where paving and revetment have cut off the supply of sediment. Threshold channels are not the authors of their own geometry. The relations presented in this tool do not apply to them.

13 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 13 PARAMETERS USED IN THIS TOOL This tool uses the following parameters: 1.Bankfull discharge Q bf in cubic meters per second (m 3 /s) or cubic feet per second (ft 3 /s); 2. Bankfull channel width B bf is meters (m) or feet (ft); 3. Bankfull cross-sectionally averaged channel depth H bf in meters (m) or feet (ft); 4. Down-channel slope S (meters drop per meter distance or feet drop per feet distance). 5. Bed surface median grain size D s50. This parameter is usually measured in millimeters (mm); the value must be converted to meters or feet in using the tool presented here. These parameters are defined before the tool is introduced. If you are familiar with the parameters, click the hyperlink to jump to the tool.tool

14 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 14 BANKFULL PARAMETERS: THE RIVER AND ITS FLOODPLAIN A river constructs its own channel and floodplain. channel floodplain At bankfull flow the river is on the verge of spilling out onto its floodplain.

15 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 15 Let  denote river stage (water surface elevation in meters or feet relative to an arbitrary datum) and Q denote volume water discharge (cubic meters or feet per second). In the case of rivers with floodplains,  tends to increase rapidly with increasing Q when all the flow is confined to the channel, but much less rapidly when the flow spills significantly onto the floodplain. The rollover in the curve defines bankfull discharge Q bf. Minnesota River and flooded floodplain, USA, during the record flood of 1965 THE DEFINITION OF BANKFULL DISCHARGE Q bf The floodplain is often somewhat poorly-developed in mountain gravel-bed streams. Bankfull stage, however, can often still be determined by direct field inspection.

16 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 16 CHARACTERIZING BANKFULL DISCHARGE Q bf Bankfull discharge Q bf is used as a shorthand for the characteristic flow discharge that forms the channel. One way to determine it is by means of direct measurement of the flow in a river. Since bankfull flow is not frequent, this method may be impractical in a river restoration scheme. Another way to estimate it is from a stage-discharge curve, as described in the previous slide. In order to implement this, the river must be gaged near the reach of interest. Another way is to estimate it using stream hydrology. It has been found that in gravel-bed streams bankfull flow is often reasonably estimated in terms of a peak flood discharge with a recurrence of 2 years (e.g. Williams, 1978 ). This corresponds to a flow discharge that has a 50% probability of occurring in any given year. When none of the above methods can be implemented, Q bf can be estimated from bankfull channel characteristics, as described in this tool.

17 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 17 CHARACTERIZING BANKFULL CHANNEL GEOMETRY: BANKFULL WIDTH B bf AND BANKFULL DEPTH H bf Bankfull geometry is here defined in terms of the average characteristics of a channel cross-section at bankfull stage, i.e. when the flow is at bankfull discharge. Here the key parameters are: bankfull width B bf and cross-sectionally averaged bankfull depth H bf. These parameters should be determined from averages of values determined at several cross-sections along the river reach of interest.

18 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 18 CAVEAT: NOT ALL RIVERS HAVE A DEFINABLE BANKFULL GEOMETRY! Rivers in bedrock often have no active floodplain, and thus no definable bankfull geometry. Highly disturbed alluvial rivers are often undergoing rapid downcutting. What used to be the floodplain becomes a terrace that is almost never flooded. Time is required for the river to construct a new equilibrium channel and floodplain. The tool presented here cannot be used to estimate bankfull discharge from bankfull channel characteristics if a) there is no floodplain or b) the channel is so disturbed that it is no longer interacting morphologically with its floodplain. Wilson Creek, Kentucky: a bedrock stream. Image courtesy A. Parola. Reach of the East Prairie Creek, Alberta, Canada undergoing rapid downcutting due to stream straightening. Image courtesy D. Andres.

19 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 19 FIELD MEASUREMENT OF BANKFULL CHANNEL GEOMETRY Not all field channels have definable bankfull geometries. Even when a channel does have a definable bankfull geometry, some experience and judgement is required to measure it. In the future a worked example complete with photographs and data files will be added to the toolbox. Until this is done, the user is urged to spend some time to determine how bankfull geometry should be determined.

20 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 20 CHARACTERIZING BED SEDIMENT IN GRAVEL-BED STREAMS: MEDIAN SURFACE SIZE D s50 Gravel-bed streams usually show a surface armor. That is, the surface layer is coarser than the substrate below. Bed sediment of the River Wharfe, U.K., showing a pronounced surface armor. Photo courtesy D. Powell. Armored surface substrate

21 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 21 SURFACE AND SUBSTRATE MEDIAN SIZES Here the surface median size is denoted as D s50 and the substrate median size is denoted as D sub50. The surface is said to be armored when D s50 /D sub50 > 1. This ratio also provides a rough estimate of ability of the stream to move its own gravel. Low values of D s50 /D sub50 (e.g. 4, relatively strong armor) are generally indicative of relatively low mean annual sediment transport rates (Dietrich et al., 1989). Notes on bed sampling, grain size distributions and the determination of median sediment size are given in and Appendix (slides 21-27) toward the end of this presentation. To jump to them click the hyperlink bed sampling.bed sampling

22 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 22 CHARACTERIZING DOWN-CHANNEL SLOPE S Down-channel bed slope should be determined from a survey of the long profile of the channel centerline. The reach chosen to determine bed slope should be long enough to average over any bars and bends in the channel, which are associated with local elevation highs and lows.

23 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 23 DATA BASE FOR THE TOOL The bankfull discharge predictor presented here was developed by Parker (2004) from the following data base for gravel-bed streams. 16 stream reaches flowing from the Rocky Mountains in Alberta, Canada (Kellerhals et al., 1972); 23 mountain stream reaches in Idaho (Parker et al., 2003); 23 upland stream reaches in Britain (mostly Wales) (Charlton et al.1978); 10 reaches along the upper Colorado River, Colorado (Pitlick and Cress, 2002) (Each reach represents an average of several subreaches.) The original data for Q bf, B bf, H bf, S and D s50 for each reach can be found in the companion Excel file, ToolboxGravelBankfullData.xls.ToolboxGravelBankfullData.xls The predictor was further tested with a set of 11 reaches in Maryland/ Pennsylvania, USA (McCandless, 2003) and 62 reaches of British streams (Hey and Thorne, 1986).

24 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 24 RANGE OF PARAMETERS USED TO DEVELOP THE TOOL Among all four sets of data, the range of parameters is as given below: Bankfull discharge Q bf (in meters 3 /sec)2.7 ~ 5440 Bankfull width B bf (in meters)5.24 ~ 280 Bankfull depthH bf (in meters)0.25 ~ 6.95 Channel slopeS ~ Surface median sizeD s50 (in mm)27 ~ 167 These ranges define the range of applicability of the tool.

25 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 25 THE TOOL The tool consists of the following relation. Where g = the acceleration of gravity (9.81 meters/second 2 or 32.2 feet/second 2 ), That is, if B bf, H bf, S and D s50 can be determined from field measurements, Q bf can be estimated from the above relation. The tool is implemented as an Excel spreadsheet in the next slide. Caution: use the relation subject to the caveats of Slides 5, 6, 7, 8 and 14!

26 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 26 IMPLEMENTATION OF THE TOOL Stop the slide show and double-click the Excel spreadsheet to activate it. If you type in the indicated input parameters in the indicated units, Q bf is computed as output. Caution: use the relation subject to the caveats of Slides 5, 6, 7, 8 and 14!

27 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 27 ACCURACY OF THE TOOL The plot shows the values of Q bf predicted by the tool versus the reported (observed) values for the data set used to develop the tool. In 93% of all reaches the predicted value is between half and twice the reported value.

28 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 28 APPENDIX: SEDIMENT SIZE DISTRIBUTIONS IN GRAVEL- BED STREAMS Implementation of the regression relations requires a knowledge of the median size of the surface armor D s50. This value must be determined by sampling the bed. In order to characterize the bed sediment of the stream the surface and substrate should be sampled separately. The results of sampling are plotted in terms of percent finer versus grain size (mm) as illustrated below. Bed sediment of the River Wharfe, U.K., showing a pronounced surface armor. Photo courtesy D. Powell. Armored surface substrate

29 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 29 WOLMAN COUNT OF SURFACE SEDIMENT The simplest way to sample a gravel bed surface is by means of a Wolman count (Wolman, 1954). The gravel surface is paced, and at set intervals a particle next to the toe of one’s foot is sampled. The sampling should be chosen so as to capture the spatial variation in bed texture. Grain size is characterized in terms of the b-axis of a grain (middle axis as measured with a caliper) or the size of the smallest square through which the grain will fit. A series grain size ranges is set for estimating the grain size distribution. In analyzing a Wolman sample, it is necessary to determine the number of grains in each range. These numbers are used to determine the grain size distribution. A sample calculation is given in the live spreadsheet of the next slide. Wolman sampling is not practical for sand-sized or smaller grains. More specifically, grains finer than about 4 mm should not be included in a sample. It should be understood that this method misses the finer grains in the surface.

30 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 30 GRAIN SIZE DISTRIBUTION FROM WOLMAN COUNT The live spreadsheet to the right shows a worked example for a Wolman count. Stop the slide show and double-click to activate it. It is customary to plot grain size on a logarithmic scale when presenting grain size distributions.

31 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 31 KLINGEMAN SAMPLE OF SURFACE SEDIMENT The methodology for a Klingeman sample of the surface sediment is outlined in Klingeman et al. (1979). A circular patch of sediment is specified on the bed. The largest grain that shows any exposure on the bed surface is located and removed. All of the bed material (including sand) is then sampled down to the level of the bottom of the hole created by removing the largest grain. The resulting sample is analyzed by mass (weight) rather than number. A Klingeman sample captures the sand as well as the gravel in the surface layer. Sampling is, however, more laborious than that required for a Wolman sample. In addition, several Klingeman samples at different locations may be needed to characterize the spatial variability of the surface sediment. A sample calculation is given in the live spreadsheet of the next page.

32 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 32 KLINGEMAN SAMPLE OF SURFACE SEDIMENT contd. The live spreadsheet to the right shows a worked example for a Klingeman sample. Stop the slide show and double-click to activate it.

33 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 33 BULK SAMPLE OF SUBSTRATE The substrate may be sampled in bulk. The surface layer is first carefully stripped off down to the depth of the bottom of the largest particle exposed on the surface. A bulk sample (e.g. cubical) volume of substrate is then excavated. According to the guidelines of Church et al. (1987), the mass (weight) of the sample should be at least 100 times the mass (weight) of the largest grain contained in the sample. Several such samples may be needed to characterize the spatial variability of the substrate. The sample is analyzed in terms of mass (weight) rather than number.

34 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 34 MEDIAN SIZE It is useful to characterize a sample in terms of its median size D 50, i.e. the size for which 50% of the material is finer. To do this, find the grain sizes D 1 and D 2 such that the percentage content F 1 is the highest value below 50% and the percentage content F 2 is the lowest percentage above 50%. The median size D 50 is then estimated by log-linear interpolation as: For example, in the Klingeman sample of slide 13: D 1 = 32 mm, F 1 = 45.24%, D 2 = 64 mm and F 2 = 59.52%. The calculation of D 50 is illustrated in terms of the live spreadsheet below. Stop the slide show and double-click to activate it.

35 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 35 REFERENCES Charlton, F. G., Brown, P. M. and R. W. Benson 1978 The hydraulic geometry of some gravel rivers in Britain. Report INT 180, Hydraulics Research Station, Wallingford, England, 48 p. Church, M. A., D. G. McLean and J. F. Wolcott 1987 River bed gravels: sampling and analysis. In Sediment Transport in Gravel-bed Rivers, Thorne, C. R., J. C. Bathurst, and R. D. Hey, eds., John Wiley & Sons, Dietrich, W. E., J. W. Kirchner, H. Ikeda and F. Iseya 1989 Sediment supply and the development of the coarse surface layer in gravel-bedded rivers. Nature, 340, Ferguson, R. I Hydraulic and sedimentary controls of channel pattern. In Rivers: Environment and Process, K. Richards. ed., Blackwell, Oxford, Hey, R. D. and Thorne, C. R Stable channel with mobile gravel bed. Journal of Hydraulic Engineering, 112(8), Kellerhals, R., Neill, C. R. and D. I. Bray 1972 Hydraulic and geomorphic characteristics of rivers in Alberta. River Engineering and Surface Hydrology Report, Research Council of Alberta, Canada, No

36 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 36 REFERENCES contd. Klingeman, P. C., C. J. Chaquette, and S. B. Hammond 1979 Bed Material Characteristics near Oak Creek Sediment Transport Research Facilities, Oak Creek Sediment Transport Report No. BM3, Water Resources Research Institute, Oregon State University, Corvallis, Oregon, June. McCandless, T. L., 2003, Maryland Stream Survey: Bankfull Discharge and Channel Characteristics of Streams in the Allegheny Plateau and the Valley and Ridge Hydrologic Regions. Report CBFO-S03-01, U.S. Fish and Wildlife Service, Chesapeake Bay Field Office, May, 33 p. Parker, G., Toro-Escobar, C. M., Ramey, M. and S. Beck 2003 The effect of floodwater extraction on the morphology of mountain streams. Journal of Hydraulic Engineering, 129(11). Parker, G Quasi-universal relations for bankfull hydraulic geometry of single-thread gravel-bed rivers. In preparation. Pitlick, J. and R. Cress 2002 Downstream changes in the channel of a large gravel bed river. Water Resources Research 38(10), 1216, doi: /2001WR000898, 2002.

37 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 37 REFERENCES contd. Williams, G. P Bankfull discharge of rivers. Water Resources Research, 14, Wolman, M.G A method of sampling coarse river bed material. Trans. Am. Geophys. Union, 35, 951–956.

38 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 38 The information on this site is subject to a disclaimer notice. Thank you for visiting the National Center for Earth Dynamics Web site and reviewing our disclaimer notice. The Web site is for informational purposes only and is not intended to provide specific commercial, legal or other professional advice. It is provided to you solely for your own personal use and not for purposes of distribution, public display, or any other uses by you in any form or manner whatsoever. The information on this Web site is offered on an “as is” basis without warranty. The readers of the information assume all risks from using the information provided herein. This tool is provided free of charge. Use this tool at your own risk. In offering this tool, the following entities and persons do not accept any responsibility or liability for the tool’s use by third parties: The National Center for Earth-surface Dynamics; The universities and institutions associated with the National Center for Earth-surface dynamics; and The authors of this tool. Users of this tool assume all responsibility for the tool results and application thereof. The readers of the information provided by the web site assume all risks from using the information provided herein. None of the above-mentioned entities and persons assume liability or responsibility for damage or injury to persons or property arising from any use of the tool, information, ideas or instruction contained in the information provided to you. Disclaimer Notice

39 National Center for Earth-surface Dynamics Stream Restoration Program Enabling Landscape Sustainability 39 Want more information? For more information on this tool or the NCED Stream Restoration Toolbox please contact the author of this tool, Gary Parker, or the NCED Stream Restoration Project Manager, Jeff Marr at National Center for Earth-surface Dynamics 2 3 rd Ave SE, Minneapolis, MN


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