Land Roughness
The three most common methods of computing friction effects fluid flow are the Chezy equation, the Darcy-Weisbach equation, and the Manning equation. For open channel flow, the Manning equation is the most common method used.
“The selection of Manning’s n values is important in the computation of water surface profiles and flow in open channels. The selected values should be representative of flow conditions at the cross section location. The cross section can be subdivided into several segments to properly represent the resistance to flow within a cross section. Normally, a natural cross section is subdivided into three segments: channel, right and left overbanks. The overbank segments can be further subdivided depending on the conditions. Manning’s n values can vary with depth of water within a segment…
“Standard textbooks and hydraulic references such as Brater and King (1976) and various NRCS and USGS books provide examples of Manning’s n values in constructed and natural channels. The refence section lists some of the available Manning’s n values references, such as U.S. Geological Survey (1967), Aldridge and Garrett (1973), U.S. Geological Survey (1989a) U.S. Army Corps. Of Engineers (USACE 2010b, Chow (1959), and Yochum (2010). Appendix A gives a procedure for estimating Manning’s n values in natural streams, floodways, and similar streams (Cowan 1956)”. [1].
Best Practices Resources
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Revision ID: 4461
Revision Date: 11/18/2022