Seattle’s Natural Drainage System (NDS) consists of stormwater management projects that use low-impact development (LID) strategies to meet multiple goals within street rights of way (ROWs), which account for 25% of Seattle’s total land surface. The projects work by infiltrating stormwater runoff, slowing it temporarily or lessening its volume, filtering, or removing pollutants through the use of soils and native plants, replacing impervious surfaces with pervious, and adding native vegetation.
NDS projects are “green,” using natural elements to mimic the ways of nature that have been lost to urbanization. Its features include open spaces, vegetated swales, stormwater cascades, and small wetlands ponds. Along with the plants and trees, there must be deep, healthy amended soils to support their growth.
While NDS projects may be better for the environment than traditional stormwater management structures, in the long term, they are usually as cost effective or even cheaper than traditional hard infrastructure as well. They also offer the advantage of being more attractive to the public than utilitarian infrastructure.