The City of Farmers Branch retained Freese & Nichols Inc. to identify locations throughout Farmers Branch Creek at risk for flooding and erosion and to develop concept-level alternatives to address these problem areas. In Phase I of the project, FNI created a hydrologic and hydraulic model to map existing and ultimate floodplains to identify structures at risk for flooding and inundation during various storm events. In addition, a geomorphologic site assessment was performed to classify portions of the reach as “high” or “moderate” erosion priority.
In Phase II of the project, FNI developed concept-level alternatives and cost estimates to address flood and erosion risk along the reach. Over half of the 61 homes identified as being in the 100-year floodplain are subject to flooding during the 10-year storm; providing flood risk reduction for smaller storm events can result in noticeable improvement for properties which are subject to frequent flooding. Therefore, this study focused on identifying alternatives to reduce flood risk during the 2-, 5-, and 10-year storm events.
FNI provided alternatives at this level for three flood risk priority areas. In addition, FNI provided erosion control project alternatives for 23 areas identified as “high” or “moderate” erosion priority in the geomorphic assessment. The project involved several public outreach efforts, which proved to be pivotal for identifying feasible solutions.
To prioritize the different project alternatives, FNI led the City staff and the City’s Municipal Drainage Utility System (Stormwater) Advisory Committee through a pairwise criteria weighting process, which allows a set of defined criteria to be ranked against each other, establishing their weight and relative importance. FNI then scored the projects according to the defined criteria to develop a ranked list of projects which reflects the City’s goals and priorities. Improvements to the Webb Chapel Road bridge ranked the highest, indicating the criticality of addressing the potential structural safety issues. In addition, the top eight projects are all erosion control projects which protect existing City infrastructure, as many of these projects lie within existing City easements and have broad system impacts.