drainage icon Drainage
Reduce flooding and improve water quality by managing stormwater through open spaces for plants and soil that absorb and infiltrate runoff and reduce impervious (hard) surfaces.


drainage area and landscape

Runoff in the Right-of-Way

This residential street was selected for a Natural Drainage Systems (NDS) project for several reasons:

First, the previous drainage system consisted of asphalt-lined ditches and culverts that ran alongside the very steep roadway. This system rapidly moved water downstream, causing unnatural amounts of stormwater to enter Piperís Creek too quickly, causing erosion to streambanks. The 110th Cascade project allows rainwater to be absorbed by the landscape naturally (infiltration) and as close as possible to where it falls.

Second, this particular street receives runoff from approximately 21 acres of the upper watershed. Installing a NDS project in this location helped to reduce downstream impacts by slowing the stormwater flow and infiltrating as much as possible. This differs from a SEA Street prototype project that only manages stormwater from the roadway and adjacent properties where it is located.

Third, most of the homes in this area of the city face north-south streets. Only two or three homes face NW 110th Street, which require less parking spaces and driveways. A larger swale design could be accommodated.