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Sizing Stream Setbacks to Help Maintain Stream Stability

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  022239,  2002 ASAE Annual Meeting . (doi: 10.13031/2013.9376) @2002
Authors:   Andy Ward, Dan Mecklenburg, John Mathews, Dawn Farver
Keywords:   bed load, effective discharge, bankfull dimensions, stormwater management, floodplain management, peak flow reduction measures

The objectives of the study were: (1) to evaluate the ability of an empirically based equation to predict the streamway width required to allow a stream to self-adjust its meander pattern; (2) to evaluate the influence of urbanization, floodplain width, and incision on bed load transport, the size of particle moved at incipient motion at flows approximating the effective discharge, and flood stage for the 100 year recurrence interval event; and to determine if knowledge obtained from Objectives 1 and 2 could be used to develop stream setback guidelines that would help avoid channel instability problems typically associated with urbanization. Empirical and practical theoretical methods were used on 6 watersheds in central Ohio. The results showed that the extent of the meander pattern for all of the watersheds was well represented by the empirical streamway width equation. An analysis of flow and bed load transport in a compound two-stage channel was performed for a series of different magnitude events that might occur during a 100 year period. The results showed that 1) floodplain width reduction, 2) entrenchment and 3) changes in flow regime each had a high potential to increase bed load transport and collectively changes in all these factors could result in a five to fifteen fold increase. The recommended approach is to establish setbacks that are a function of the meander belt width as calculated by an empirical equation that is based on the drainage area. Also, land uses within the setback zone should be restricted to uses that sustain or enhance the ecological function of the system and accommodate the stream in a state of dynamic equilibrium. Based on a previous study by the authors it is also recommended that storm water management strategies be used expressly to control bed load sediment transport rates.

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