30th Ave. N. & E. Denny Way
Seattle, WA USA

Fall 2010

Madison Valley - Stormwater Improvements

Shaped by a glacier and eroded by floods, the Madison Valley drainage basin has steep hillsides and was once drained by a stream that emptied north into Union Bay via what is now the University of Washington Arboretun. Beginning in the late 1860's, Madison Street was etched across the basin - first a wagon road, then a cable railway with a trestle across the valley. In the early 1900's, the trestle was replaced with fill, which blocked the natural watercourse, and a combined sewer trunk pipe was built to carry sewage and stormwater under the fill and northward. For several decades, the storm/sewer pipe system has been inadequate to address significant rain fall into the valley; on Augus 2004 storm events flooded yards basements to 5 feet, the December 2006 flood claimed the life of a valley resident.

In 2006, SPU began construction of a surface stormwater storage facility at 20th Ave. E. and E. John St., an area that experienced the worst historic flooding. Following the catastrophic December 2006 floods, SPU increased the scope of the project: Phase 1 expands the surface facility to provide 1.8 million gallon of storage; Phase 2 extends a 48-inch north to Washington Park, and constructs an additional 2.2 million gallons of surface and underground stormwater storage.

Site enhancement at the Phase 1 site improved the detention basin spaces to make them a neighborhood natural amenity. The design provides a curvilinear, accessible path from the southwest through the basin, atop a rack gabion bridge that crosses a (usually) dry creek bed to an overlook and a direct route up the east bank. There is an informal route that follows the creek bed connecting the north and south access points. The southwest corner entry provides a water feature stone and sand area for small children, tables and broad playful stone steps into the rolling lawn terraces providing amphitheatre seating which wrap the basin to capture sunlight. The landscape is a microcosm of the valley restored, which all native plantings, local stone, and an intermittent creek flow.

Artist Adam Kuby has developed site piece to tell the natural and cultural history of the valley and to reveal the function of the site in stone and plantings.