Projects & Programs
I-405 Low-Impact Development Project
An analysis of watershed conditions within the North Renton I-405 project area was conducted by PNNL using existing geographic information system data. Subwatersheds within the study area were evaluated based on natural land-cover conditions and human land-use influences. This land-use and land-cover (LULC) analysis was used to prioritize subwatersheds for aquatic resource conservation and restoration. In addition, the potential impacts of the proposed expansion of the I 405 right-of-way highway corridor were evaluated based on localized LULC analysis. Recommendations were made regarding possible mitigation projects as well as stream protection strategies and potential stream restoration projects. May Creek was determined to be best suited for protection and restoration opportunities, followed by the lower Cedar River, Coal Creek and Kelsey Creek.
In addition to the watershed assessment task, the proposed I-405 North Renton project was evaluated for the potential use of innovative stormwater management techniques. These innovative techniques can be described as natural stormwater management (NSWM) or low-impact development (LID) methods of stormwater treatment. These NSWM-LID techniques generally fall outside the realm of “conventional” stormwater best management practices required by current regulations. Typical NSWM-LID techniques rely heavily on the use of infiltration-based systems to reduce runoff and on natural vegetation to enhance stormwater quality. In addition, the reduction of impervious surface area and the elimination of pollutant sources are key elements of this strategy. A NSWM-LID concept plan was developed for the North Renton I-405 Project area, including recommendations for best management practices placement and an estimate of potential effectiveness in reducing the impacts of the highway expansion project on aquatic resources.