Pacific Southwest

Title: Coupling hydrodynamic modeling and empirical measures of bed mobility to assess the risk of redd scour on a large regulated river

Author: May, Christine L.; Pryor, Bonnie S.; Lisle, Thomas E.; Lang, Margaret M.

Date: 2009

Source: Water Resources Research

Description: n order to assess the risk of scour and fill of spawning redds during floods, an understanding of the relations among river discharge, bed mobility, and scour and fill depths in areas of the streambed heavily utilized by spawning salmon is needed. Our approach coupled numerical flow modeling and empirical data from the Trinity River, California, to quantify spatially explicit zones of differential bed mobility and to identify specific areas where scour and fill is deep enough to impact redd viability. Spatial patterns of bed mobility, based on model‐predicted Shields stress, indicate that a zone of full mobility was limited to a central core that expanded with increasing flow strength. The likelihood  and maximum depth of measured scour increased with increasing modeled Shields stress. Because redds were preferentially located in coarse substrate in shallow areas with close proximity to the stream banks, they were less likely to become mobilized or to risk deep scour during high-flow events but were more susceptible to sediment deposition.

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Citation

May, Christine L.; Pryor, Bonnie S.; Lisle, Thomas E.; Lang, Margaret M.  2009.  Coupling hydrodynamic modeling and empirical measures of bed mobility to assess the risk of redd scour on a large regulated river.   Water Resources Research .