Mugal Dahal
Washington State University
Stormwater runoff is a primary carrier of pollutants to the nearby streams and lakes.
Green stormwater infrastructure (GSI) is built to intercept stormwater runoff to mitigate peak flows and stormwater pollutants before reaching surface waters.
A rain garden is a type of GSI comprising a plant-soil system where water retention is maximized through infiltration and storage. Proper placement of rain gardens within the watershed is crucial to maximizing their cost-effectiveness.
The Lower Puyallup River Watershed, situated in South Puget Sound, consists of primarily residential areas of the cities of Puyallup and Tacoma.
Preservation of water quality is essential as the streams and rivers in the watershed are critical aquatic habitats for Chinook and Coho salmon return for spawning.
The study’s objective is to develop a framework to identify suitable sites for rain gardens in an urbanizing watershed.
An indexing approach to identify Hydrological Sensitive Areas (HSA) was adopted, in which we consider the topography, runoff contributing area, soil depth, and hydraulic conductivity. The Topographic Wetness Index (TWI) and Soil Water Storage Capacity (SWSC) were computed to obtain the Hydrologic Sensitivity Index (HSI).
Areas considered infeasible per criteria specified by state and county regulations were removed, and HSI was classified based on suitability for the construction of rain gardens.
This study provides a practical, scalable, and portable tool for prioritizing the placement of GSI for stormwater runoff management.