HYDRAULIC ANALYSIS OF FOREST HILLS SUBDIVISION
The challenge was to determine existing flooding conditions within the Forest Hills subdivision, evaluate the proposed “relief” storm sewer that was sized by others, and evaluate the impact of this relief storm sewer on all downstream properties. DesignTek obtained key topographic information throughout the existing Forest Hills subdivision. This information included known high water marks, critical overland flow points and elevations, cross sections through these existing overland flow routes, and complete topography of the area of major flooding to gain existing storage volume information. Using the TR20 computer program, DesignTek determined existing runoff to the depressional areas within the subdivision, evaluated ponding depths considering the existing release from the depressed area through existing storm sewers and overland flow routes, and then evaluated the same conditions with the proposed storm sewer pipe in place. Since the addition of the storm sewer created an increase in flow to the downstream properties, DesignTek then needed to model this increased flow from Forest Hills south through an existing culvert under 95th Street, through the existing Las Fuentes subdivision, and ultimately into Belly Deep Slough. This evaluation was used to gain approval from the receiving property owners so that the proposed relief sewer could be installed without legal objection from these downstream owners.