Reach Routing: Difference between revisions
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“Two important judgements are needed by the engineer when developing data for channel reach routing. One is the selection of a representative cross section. This cross section should represent an average flow velocity through the reach. If there are several cross sections available for selection, the engineer should select the section most typical of the reach conditions. The second important judgement is the selection of a reach length. To properly represent reach storage characteristics, the reach length should be an average length of the routing reach. HEC-RAS allows for left overbank, right overbank, and channel reach lengths. WinTR-20 allows for only floodplain length and channel length. WinTR-55 is limited to only a single channel length”.<ref name="NEH210-630-17">[[ | “Two important judgements are needed by the engineer when developing data for channel reach routing. One is the selection of a representative cross section. This cross section should represent an average flow velocity through the reach. If there are several cross sections available for selection, the engineer should select the section most typical of the reach conditions. The second important judgement is the selection of a reach length. To properly represent reach storage characteristics, the reach length should be an average length of the routing reach. HEC-RAS allows for left overbank, right overbank, and channel reach lengths. WinTR-20 allows for only floodplain length and channel length. WinTR-55 is limited to only a single channel length”.<ref name="NEH210-630-17">[[National Engineering Handbook: Chapter 17 - Flood Routing | National Engineering Handbook: Chapter 17 - Flood Routing, NRCS, 2014]]</ref> | ||
“Storage in a reach is often underestimated because backwater storage in tributaries is usually not considered in developing water surface profiles using HEC-RAS. If this type of storage is significant, it should be estimated. The simplest way to account for this would be to increase the floodplain length. A more complex analysis would involve adjusting HEC-RAS cross sections to include an ineffective flow area for tributary backwater”. <ref name="NEH210-630-17"/> | “Storage in a reach is often underestimated because backwater storage in tributaries is usually not considered in developing water surface profiles using HEC-RAS. If this type of storage is significant, it should be estimated. The simplest way to account for this would be to increase the floodplain length. A more complex analysis would involve adjusting HEC-RAS cross sections to include an ineffective flow area for tributary backwater”. <ref name="NEH210-630-17"/> | ||
==Best Practices Resources== | ==Best Practices Resources== | ||
{{Document Icon}} [[ | {{Document Icon}} [[National Engineering Handbook: Chapter 6 - Stream Reaches and Hydrologic Units | National Engineering Handbook: Chapter 6 - Stream Reaches and Hydrologic Units (Natural Resources Conservation Service)]] | ||
{{Document Icon}} [[ | {{Document Icon}} [[National Engineering Handbook: Chapter 17 - Flood Routing | National Engineering Handbook: Chapter 17 - Flood Routing (Natural Resources Conservation Service)]] | ||
{{Document Icon}} [[Flood Hydrology Manual|Flood Hydrology Manual (Bureau of Reclamation)]] | {{Document Icon}} [[Flood Hydrology Manual | Flood Hydrology Manual (Bureau of Reclamation)]] | ||
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Revision as of 19:39, 21 October 2022
“Two important judgements are needed by the engineer when developing data for channel reach routing. One is the selection of a representative cross section. This cross section should represent an average flow velocity through the reach. If there are several cross sections available for selection, the engineer should select the section most typical of the reach conditions. The second important judgement is the selection of a reach length. To properly represent reach storage characteristics, the reach length should be an average length of the routing reach. HEC-RAS allows for left overbank, right overbank, and channel reach lengths. WinTR-20 allows for only floodplain length and channel length. WinTR-55 is limited to only a single channel length”.[1]
“Storage in a reach is often underestimated because backwater storage in tributaries is usually not considered in developing water surface profiles using HEC-RAS. If this type of storage is significant, it should be estimated. The simplest way to account for this would be to increase the floodplain length. A more complex analysis would involve adjusting HEC-RAS cross sections to include an ineffective flow area for tributary backwater”. [1]
Best Practices Resources
National Engineering Handbook: Chapter 17 - Flood Routing (Natural Resources Conservation Service)
Flood Hydrology Manual (Bureau of Reclamation)
Citations:
Revision ID: 3993
Revision Date: 10/21/2022