Level 1 Analysis for the Harris County Watershed Master Plan

Harris County, located on the Texas Gulf Coast, is one of the largest counties in Texas with a growing population approaching 4 million residents. Each year, the entire county typically experiences several severe floods that cause structural damage, traffic disruption and neighborhood degradation. With annually reoccurring damage and the threat of more serious flood events, the Harris County Flood Control District (HCFCD) is committed to improving the flood control system of the entire County. This involves addressing the existing issues as well as preventing potential problems that may occur with expected new development. With 22 watersheds and 1,788 square miles of land, a comprehensive plan will take many years and millions of dollars to develop. HCFCD's initial phase of this undertaking is the Level 1 planning concept, with the objectives of: 1) Comprehensive planning in all watersheds, 2) Addressing drainage issues for the entire HCFCD conveyance system, 3) Determining costs for solutions over a range of protection levels, and 4) Determining the needed corresponding right of way. HCFCD and the Watershed Master Plan (WMP) team developed an analysis procedure to meet these objectives in an appropriate time frame. Key elements of this approach include: 1) Mainstem conveyance analysis, 2) Tributary conveyance analysis, and 3) Detention requirements for future development. The conveyance analyses focus on increasing the storage area within the existing channel to confine the required runoff based on the desired level of service. The detention solutions are developed by determining the needed detention size to confine the required expected runoff from the currently undeveloped areas. The hydrology and hydraulic software used in these approaches include HEC-RAS, HEC-HMS and a custom program for volume-based detention design. These analyses are all preformed for 10%, 4% and 1% levels of service and compare required costs and resources for each level. This analysis has already been completed for Goose Creek and Greens Bayou. The results show required geometry for specified design storms as well as additional right of way areas required for channel improvements. These areas will help HCFCD to plan for future channel improvements in order to minimize future flooding from high intensity storm events.