Hi-Tech Habitat: How GIS Can Help Evaluate the Effects of Restoration on Salmon

The Cedar River originates in the Cascade Range and is the center of the Cedar River watershed – the source of Seattle’s drinking water.  Running approximately 45 miles alongside the Cedar River Trail, the Cedar River is popular for recreation and is also home to various aquatic wildlife, including chinook, coho, and sockeye salmon.

In 2020, Herrera’s GIS team began a study to develop a best available science (BAS) report to evaluate the effects of King County capital project design elements on salmonid habitat along the Cedar River. Herrera hopes the study will help the County develop repeatable metrics to measure wood and habitat and to assess whether remotely sensed data such as LiDAR and high-resolution aerial desktop photos can provide the same level of detail as in-person site reconnaissance.  

If successful, the County will be able to target future field efforts on areas that were once difficult to assess accurately from a computer screen. The Herrera team also plans to run statistical analyses to determine whether previous floodplain restoration projects achieved or exceeded the standard for no net loss of salmonid habitat.

As a paired study design, Herrera is evaluating two “treatment” reaches (reaches where restoration projects have been implemented), with a control site for each reach. When determining treatment and control pairs, scientists looked for sites having similar geomorphic characteristics based on factors such as comparing GIS relative elevation models. In addition, this study includes two reference reaches. To help support the County in digitizing historic wood data, we are developing a GIS-based large wood delineation tool. This tool will standardize data collection and auto-calculate wood characteristics, such as planform blockage ratio and orientation. with the result will be a repeatable tool that can help minimize differences in how wood is mapped between observers and projects over time.

Herrera is excited to continue to study and answer these questions with a goal to have recommendations by Spring 2022.