Browne’s Mountain is an area within Spokane County that has been developed in the past 10 years without adequate stormwater management planning. Storm sewers were constructed in the upper portions of the developments that were discharged to the street surface part way down the mountain. This caused severe flooding and property damage to residents and streets.
Century West provided a plan for the area that evaluated various alternatives for managing the stormwater runoff from these developments. Capacity restrictions in a drainage ditch at the bottom of the mountain required that detention structures be included in the plan. The drainage basins were identified using County GIS information and computer modeled using both HEC 1 and HYDRA to determine storm hydrographs and peak flows. Storm sewers were sized to collect runoff and two alternative stormwater detention ponds were evaluated. Century West used results from the HEC 1 model and the computer model Pond-2 to determine required pond sizes. Cost estimates were developed for each alternative and recommendations were made for type and size of facilities and project phasing.