Channel-Bed Scour with High versus Low Deflectors

Abstract

Deflectors are recognized as one of the best devices for enhancing deep-water habitat in low-gradient channels. Modern design standards recommended the use of low-profile structures intended to function primarily at a lower stage, but research suggests that pools are typically formed by larger magnitude flows. A flume experiment was conducted in a 0.5-m wide, 6-m long recirculating flume to determine the volume of pool habitat and maximum depth of scour created by low versus high deflectors. Although the high deflectors were 1/3 the width of low deflectors, they created larger volume pools for all flows above bankfull levels. Pools were also as deep or deeper for high deflectors under the larger-flow conditions. Existing deflectors along the Blackledge River, Conn. support these two observations. Conversely, low deflectors produced deeper larger pools for discharges below bankfull levels. These results suggest that high deflectors may be better suited for creating pool habitat, especially in coarse-bedded channels.