WPA Landslide Drainage Systems Assessment

(Seattle, WA)  Landau Associates provides Seattle Public Utilities (SPU) with programmatic geotechnical engineering services related to assessment and evaluation of a series of landslide mitigation systems that were constructed in the 1930s as part of a Works Progress Administration (WPA) program. The systems are composed of 30 distinct systems in known landslide hazard areas within metropolitan Seattle and consist of an estimated 20,000 feet of drainage trenches or tunnels ranging in depth from 15 to 100 feet below the ground surface. SPU had undertaken various evaluations of these systems over the years, but the evaluations were plagued by the lack of available information and uncertainties regarding the systems. SPU retained Landau Associates to develop a comprehensive and systematic process for evaluating the slopes and the role of the existing drainage systems in their stability, and for assessing relative risk and prioritization of maintenance and system improvements.

Limited information is available regarding the existing systems and SPU calls upon Landau Associates periodically to fulfill the task of collecting and compiling all available data into a spatial database to assess the changes at various site locations over time. Landau Associates then conducts evaluations of accessible segments of the landslide mitigation systems and evaluates site conditions, often using CCTV video surveys. The objective is to assist SPU in evaluating the condition of the drainage systems, the current effectiveness of the system in stabilizing the affected hillside, and quantifying the risks associated with the system. 

Photo 2 & 3: City of Seattle