Hydraulic Properties of the Riffle Crest and Applications for Stream Ecosystem Management

Abstract

AbstractRiffle crests are important hydraulic controls in riffle‐pool‐dominated streams, influencing pool hydraulics and water quality that collectively control lotic habitat for many organisms. We define a simple stream depth measurement, the riffle crest thalweg (RCT), describe measurement methods and utility, and suggest that RCT depth is a better independent variable than streamflow (Q) for many instream flow and habitat assessment applications. Using RCT depth as an independent variable, rather than streamflow, reduces the need for gauging or streamflow measurements in many management applications. Unlike streamflow, RCT depth varies directly with fundamental elements of riverine habitat such as channel morphology and bed roughness. We also suggest that relationships between RCT depth and streamflow (RCT‐Q curves) can be used to evaluate the risk of streamflow alteration at ungauged sites. We describe three case studies to demonstrate the utility of RCT depth and RCT‐Q rating curves in stream ecosystem management: (1) evaluating the effect of a top‐down flow prescription on modeled salmonid habitat, (2) estimating the risk from the incremental reduction of RCT depth on habitat and ecological responses, and (3) identifying relationships between RCT depth and dissolved oxygen in ungauged streams. An easy‐to‐measure, inexpensive, and ecologically sensitive metric, RCT depth holds promise as a useful tool in stream ecosystem management.