Stormwater flows downhill, in this case a steep slope into the Piper Creek Watershed, near Venema in Seattle. This slope, at times exceeding 10%, provided a challenge for construction. How to keep sediments from the construction from contaminating the watershed and clogging the native soils used for infiltration?
In this installation, straw wattles, plastic sheeting, and filter socks in storm drains were used extensively. The Bioretention cells used the slope, using steps to slow the flow of the water. At the top of the slope where several pipes feed into the bioretention cells, there is a small settling pond to keep excess sediment out of the water as well as slowing the flow to protect the cells.