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Chapter 5--Stream Hydrology United States Department of Part 654 Stream Restoration Design Agriculture National Engineering Handbook Natural Resources Conservation Service Chapter 5 Stream Hydrology Chapter 5 Stream Hydrology Part 654 National Engineering Handbook Issued August 2007 Cover photo: Quantifying the flow of the stream involves analysis of rain- fall/runoff, storm recurrence intervals, and watershed and flood plain conditions. Advisory Note Techniques and approaches contained in this handbook are not all-inclusive, nor universally applicable. Designing stream restorations requires appropriate training and experience, especially to identify conditions where various approaches, tools, and techniques are most applicable, as well as their limitations for design. Note also that prod- uct names are included only to show type and availability and do not constitute endorsement for their specific use. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720–2600 (voice and TDD). To file a com- plaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, SW., Washing- ton, DC 20250–9410, or call (800) 795–3272 (voice) or (202) 720–6382 (TDD). USDA is an equal opportunity pro- vider and employer. (210–VI–NEH, August 2007) Chapter 5 Stream Hydrology Contents 654.0500 Purpose 5–1 654.0501 Introduction 5–1 654.0502 Overview of design discharges 5–2 (a) Low flows .........................................................................................................5–2 (b) Channel-forming discharge ............................................................................5–2 (c) High discharge .................................................................................................5–2 (d) Flow duration ..................................................................................................5–3 (e) Seasonal flows .................................................................................................5–3 (f) Future flows .....................................................................................................5–3 (g) Regulatory ........................................................................................................5–3 654.0503 Probability 5–4 654.0504 Gage analysis for flow frequency 5–6 (a) Analysis requirements and assumptions ......................................................5–6 (b) Frequency distributions ................................................................................5–10 654.0505 Regional regression 5–34 (a) Basic concepts ...............................................................................................5–34 (b) Regional analysis ..........................................................................................5–35 (c) Computational resources for regional regression analysis of peak .........5–37 flows 654.0506 Flow duration 5–37 654.0507 Hydrologic models 5–39 654.0508 Channel-forming discharge 5–41 (a) Cautions and limitations ...............................................................................5–53 654.0509 Other sources of design flows 5–53 654.0510 Conclusion 5–54 (210–VI–NEH, August 2007) 5–i Chapter 5 Stream Hydrology Part 654 National Engineering Handbook Tables Table 5–1 Sensitivity analysis on gage record, Willow Creek case 5–8 study Table 5–2 K-values for the Gumbel extreme value distribution 5–12 Table 5–3 K-values for the log-Pearson type III distribution 5–13 Table 5–4 Discharge peaks, with basic statistics 5–15 Table 5–5 Outlier test Ko values, from WRC Bulletin 17B 5–20 Table 5–6 Peak streamflow data at gage 06324500 Powder River 5–24 at Moorhead, MT Table 5–7 Logarithmic data and Weibull plotting position values 5–26 Table 5–8 Frequency analysis data at gage 06324500 Powder River 5–27 at Moorhead, MT Table 5–9 Historic methodology computations 5–28 Table 5–10 Summary of bankfull indices 5–43 Table 5–11 Summary of stream conditions that affect bankfull 5–44 indices Table 5–12 Effective discharge calculation from SAM program 5–49 Figures Figure 5–1 Plotting distributions for return period peak discharges 5–17 Figure 5–2 Data plot at gage 06324500 Powder River at Moorhead, 5–25 MT Figure 5–3 Data and frequency plots 5–25 Figure 5–4 Sheet 1 of log-Pearson spreadsheet output for 5–29 USGS gage 0825150 Figure 5–5 Sheet 2 of log-Pearson spreadsheet output for USGS 5–30 gage 08251500 Figure 5–6 Sheet 3 of log-Pearson spreadsheet output for USGS 5–31 gage 08251500 5–ii (210–VI–NEH, August 2007) Chapter 5 Stream Hydrology Part 654 National Engineering Handbook Figure 5–7 100-yr discharges for the Rock Creek watershed in 5–33 Montgomery County, MD Figure 5–8 Typical flow-duration curve 5–38 Figure 5–9 Five basic submodels of a rainfall/runoff model 5–41 Figure 5–10 Bankfull discharge as a function of drainage area for 5–45 the Salmon River, ID Figure 5–11 Effective discharge calculation 5–47 Figure 5–12 Flow-duration curve developed from 39 years of records 5–48 at a USGS gage downstream from the project reach Figure 5–13 Sediment transport rating curve calculated from 5–48 bed material gradation collected upstream from the project reach and hydraulic parameters from surveyed cross section Figure 5–14 Effective discharge calculation 5–48 (210–VI–NEH, August 2007) 5–iii Chapter 5 Stream Hydrology 654.0500 Purpose 654.0501 Introduction Stream restoration design should consider a variety Hydrologic analysis has historically been the starting of flow conditions. These flows should be considered point for channel design. Current and future flows from both an ecological, as well as a physical perspec- were estimated, then the designer proceeded to fur- tive. Many sources and techniques for obtaining hydro- ther analysis. However, the complexities of stream res- logic data are available to the designer. This chapter toration projects often require that hydrologic analysis provides a description of the flows and their analyses be conducted in close coordination with a study of that should be considered for assessment and design. stream geomorphology and stream ecology. The computation of frequency distributions, with an emphasis on the log-Pearson distribution as provided Hydrologic computations are an integral part of any in the U.S. Water Resources Council (WRC) Bulletin stream design and restoration project. However, de- 17B, is addressed in detail. Examples have been pro- sign objectives for a stream restoration project cannot vided to illustrate the methods. Transfer equations, adequately be met by assessing channel behavior for risk, and low-flow methods are also addressed. Finally, only a single discharge. A stream restoration project this chapter describes advantages and limitations of usually has several design flows selected to meet vari- four general approaches widely used for estimating ous objectives. For example: the channel-forming discharge or dominant discharge. • Estimates of future flow conditions are often required to properly assess project perfor- mance over the long term. • Estimates of low flows such as 7-day low flow often define critical habitat conditions. • Estimates of channel-forming discharges are used to estimate stable channel dimensions. • Flood flow estimates are used to assess stabil- ity of structures and flood plain requirements, as well as for scour depth prediction. Many techniques are available to the designer for determining the various discharges used in assessment and design. The level of accuracy required for the different hydrologic analyses, as well as the need to estimate the different flows, is dependent on the site- specific characteristics of each project. Therefore, it is important to understand not only what each design flow represents, but also the underlying assumptions and the limitations of the techniques used to estimate the flow. (210–VI–NEH, August 2007) 5–1 Chapter 5 Stream Hydrology Part 654 National Engineering Handbook • bankfull indices 654.0502 Overview of design • effective discharge discharges • specific recurrence interval • drainage area A description of some of the various types of design discharges is provided in this section. Although a The distinction between channel-forming discharge project may not require the use of all of these flows and the other deterministic discharges is frequently for design, the hydraulic engineer/designer should still confused, as the terms are used interchangeably. This consider how the project will perform during a range chapter describes advantages and limitations of the of flow conditions. four widely used general approaches. (a) Low flows (c) High discharge Design of a low-flow channel may be required as part The reaction of a channel to a high discharge can of a channel restoration. Normally, the design of the be the impetus for a stream restoration project. An project for low flows is performed to meet biologi- identified high-flow event is often used in the design cal goals. For instance, summer low flows are
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