S.M. Stemper Architects as Prime, in conjunction with Susan Black & Associates as a subconsultant, provided analysis, design and construction oversight for this extensive rain garden to address flooding from off-site City of Seattle streets and roofs. Lynn Hall, located on the campus’ north edge, is situated at the lowest point of the campus along Madison Avenue. For decades, stormwater repeatedly flooded the building and large areas of the campus by breaching the curb and flowing south through the heart of the campus. Facilities Management sought a design solution that minimized disruption and environmental impact to the campus.
RAIN GARDEN SITE & MASTER PLAN: As part of waterproofing the building, a comprehensive rain garden system was designed. The system includes the collection of rainwater from the roof and a concrete apron at the base of the building into a French drain, which leads to the rain garden. The concrete apron seals a deep interceptor drain further protecting the building from rainwater. A series of planted, modular “pods” were installed on the concrete apron to detain stormwater and improve the appearance along the building. Vegetation that can withstand water-soaked conditions was planted.
100 YEAR STORM OUTCOME: Just one week after completion, the rain garden was put to the test when Seattle received a 100-year storm resulting in 5.4 inches of rain in a 24-hour period. The rain garden system performed as expected keeping Lynn Hall dry and draining water in the garden. The rainfall exceeded the capacity of the rain garden whose design allowed overflow into the city’s stormwater system.