City of Harker Heights Stormwater Master Plan (Ph. I & II)
Rapid growth has been prevalent within the City of Harker Heights for decades due to the City’s proximity to the largest military installation in the U.S. Overwhelming growth created the need for a comprehensive Drainage Master Plan to evaluate the City’s current and projected future needs. In addition to the City’s need for a Drainage Master Plan, the City would greatly benefit from an up to date set of City planimetric maps.
In 2008, updated FEMA floodplain maps became the new standard. Unfortunately, numerous structures historically excluded from the floodplain were now included within the floodplain, requiring property owners to carry expensive flood insurance. The residences abutting Trimmier Creek were some of the most impacted by the newly published maps. Public Works staff wanted to aid the local residents by determining a way to remove the properties from the floodplain. The City reached out to a long standing teammate, Walker Partners, for assistance with their project.
Walker Partners performed field surveys of the existing culverts and channels. As a supplement to the field survey, a new aerial survey was conducted for the entire incorporated limits of the City, including a high resolution aerial photograph background. The updated planimetric maps were instrumental in producing accurate floodplain maps and are used today for a wide variety of planning applications via the City’s GIS system.
Industry leading computer software by Autodesk Civil 3D, was used to compile all of the field-collected data for each of the identified streams. HEC-HMS and HEC-RAS computer software, created by the Army Corps of Engineers, was used to produce hydrologic and hydraulic models of the streams. HEC-HMS was used to determine the hydrology within each stream basin for the 10-year, 50-year, and 100-year events. Utilizing the runoff rates from the HEC-HMS model and the survey data, HEC-RAS was used to generate water surface profiles for each of the modeled streams.
Following the completion of the stream modeling, high-risk flood areas were identified, which were used to assemble a recommended list of Capital Improvement Projects (CIP). The recommend improvements were modeled within HEC-RAS and preliminary cost estimates were prepared for each potential CIP. The CIPs were ranked and prioritized using engineering judgment, opportunity, and project costs.
The City embraced the proposed Capital Improvement Program and immediately began to implement the CIP recommendations included in their Drainage Master Plan. Upon completion of each of the CIP improvements, the City is planning on filing a FEMA LOMR for each stream. As a result of the Drainage Master Plan, the residents of Harker Heights will not only see a significant improvement in their quality of life, but the LOMRs are anticipated to remove a large number of homes from the FEMA floodplain. Once the residents are removed from the floodplain, they will not be burdened with the high cost of flood insurance premiums.