Update to the Toe‐Width Methodology: Determining Preferred Discharges for Spawning and Rearing Salmonids

The impacts of changing streamflow on fish habitat are often assessed using instream flow methodologies that relate changes in streamflow to changes in habitat availability. Direct measurements of the streamflow‐to‐habitat relationship are time consuming and not feasible to do on all streams. Measuring the width of the stream channel for species‐specific regression equations (referred to as the toe‐width method) provides a quick and cost‐effective estimate of the preferred spawning and rearing discharges for specified fish species. Despite continued use of the toe‐width method since the late 1970s, it has not been updated or tested against more modern methods. We designed a clearer methodology for identifying and measuring the toe‐width in Washington State. We used preferred discharges from 69 fish‐habitat‐to‐streamflow studies compared with the toe‐width at these study sites to develop new equations and tested the new methodology for reproducibility. Additionally, all fish‐habitat‐to‐streamflow studies used the latest version of Washington State's habitat suitability criteria. The three indicators used to locate the toe of the bank and the three channel characteristics used to select toe‐width transect locations result in reproducible measurements. All the updated toe‐width regression equations for spawning and rearing salmonids had lower percent standard errors than the original methodology. Our instructions and subsequent testing of the revised method with varied samplers provide us with confidence that the updated methodology is a more understandable, accurate, and consistent way to identify the toe of the bank and to measure the toe‐width.