Greening Stormwater Infrastructure: Integrating Low-Impact Development with Traditional Methods in Washington State

Low impact development (LID) is emerging as the latest generation in strategies to manage stormwater. The LID approach has moved beyond the acceptance stage and implementation is encouraged at a much wider scale. The current challenge for stormwater managers is how to integrate newer practices with traditional stormwater management methods, both in terms of meeting regulatory standards and existing stormwater infrastructure. Due to limiting glacial soils commonly found in the Puget Sound region, LID techniques alone often cannot eliminate the use of traditional detention. These challenges require a more layered approach to implement LID where practicable to complement the existing infrastructure or application of traditional methods. In this paper, the efforts of two established Puget Sound communities to integrate LID with existing stormwater standards will be reviewed. The City of Bellevue has developed a Natural Drainage Practices (NDP) Manual to provide methods for evaluating site conditions, selecting and sizing appropriate practices, and calculating credits toward meeting the City's stormwater management requirements. In the City of Burien, an LID Implementation Plan is being developed to identify regulatory gaps for adopting LID, create a toolbox for implementing practices, and educate the public on LID. The Burien toolbox will include updated standard details of natural drainage practices, alternative LID road standards, and checklists for siting and designing small-scale practices.