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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2017. Guidance for Design Hydrology for Stream Restoration and Channel Stability. Washington, DC: The National Academies Press. doi: 10.17226/24879.
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1 Significant resources are being applied by public and private road and rail organizations to design and construct restored streams in disturbed watersheds, as well as to provide for stable transportation crossings (bridges and culverts) of streams. Lacking in this effort is a scientifically supported method for defining the design hydrology for such efforts along with an understand- ing of how that design hydrology might change with land use changes. Current practice in hydrologic design of stable channels at stream crossings focuses on a single “dominant” discharge that is assumed to be a reasonable surrogate for the entire range and temporal sequence of channel-forming flows. The channel-forming discharge is typically identified and “bankfull” field indicators (a challenging task even in minimally disturbed chan- nels), recurrence interval analysis of peak flows (often extrapolated from gaged to ungaged sites), regional flood regression relationships, or a combination of these methods. Such methods can be problematic because they oversimplify the physical controls on channel form and response, and frequently result in channel designs that are unstable. A more robust alternative to stable channel design hydrology has converged on the idea that a sediment continuity or “sediment impact analysis” should underpin the design of most alluvial channels (Copeland et al. 2005; Soar and Thorne 2001, 2011; Natural Resources Conservation Service (NRCS) 2007; Shields et al. 2003, 2008; Doyle et al. 2007), especially fine-grained or “labile” channels. One of the greatest impediments to adoption of these methods in practice has been the lack of (1) decision support and analysis tools for discerning which design situations require such an analysis and (2) practical tools generating key inputs and performing the analy- ses. This document addresses this gap by summarizing guidance and a set of decision support tools that are scientifically based and practical. The decision support tools presented herein are intended to be flexible and efficient in guiding users to an appropriate combination of design tools and depth of analysis for design hydrology in a given hydrologic and geomorphic setting. Additional data and effort are only required when necessary for the channel type and design situation of interest. Introduction C h a p t e r 1

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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 853: Guidance for Design Hydrology for Stream Restoration and Channel Stability provides written guidance and interactive tools to help hydraulic engineers assess the current conditions adjacent to a stream crossing and in the upstream watershed. Specifically, the guidance and tools provide support in assessing the current conditions adjacent to a stream crossing and in the upstream watershed to determine design effort, performing the appropriate hydrological and geomorphic analysis using a set of analytical and analog tools, and designing the channel through the stream crossing for stability and sediment balance.

In addition to the report, users can download the contractor’s final report; the spreadsheet-based Capacity Supply Ratio Stable Channel Design Tool (CSR Tool) for computing analytical channel designs that account for the full spectrum of sediment transporting events; an example of the CSR Tool being used on a sand bed stream (Big Raccoon); and an example of the CSR Tool being used on a gravel/cobble bed stream (Red River).

Disclaimer - This software is offered as is, without warranty or promise of support of any kind either expressed or implied. Under no circumstance will the National Academy of Sciences, Engineering, and Medicine or the Transportation Research Board (collectively "TRB") be liable for any loss or damage caused by the installation or operation of this product. TRB makes no representation or warranty of any kind, expressed or implied, in fact or in law, including without limitation, the warranty of merchantability or the warranty of fitness for a particular purpose, and shall not in any case be liable for any consequential or special damages.

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