The Round Rock Watershed Modelling Review, Texas

09 Jan 2015

RPS recently contracted with the City of Round Rock, Texas to conduct a detailed review of Upper Brushy Creek (UBC) watershed hydrologic and hydraulic models recently prepared by the UBC Water Improvement District.

These models and the associated mapping will be used by the Federal Emergency Management Agency (FEMA) in developing up-to-date Digital Flood Insurance Rate Maps (DFIRM) within the UBC watershed. The review covered approximately 162 square miles of contributing drainage area and 46 miles of stream that were respectively modeled with the hydrologic model, HEC-HMS, and the hydraulic model, HEC-RAS, with a majority of the watershed located within the City’s Extra Territorial Jurisdiction (ETJ). RPS’ review ensured the study results are as accurate as possible by focusing on the modeling methods and techniques used and assessing 11 NRCS Dams and other stormwater infrastructure within the watershed. The final FEMA models and related maps will assist the City in the determination of local flooding impacts as well as help determine stormwater Capital Improvement Project needs and the solutions required.

As a direct result of the areas identified as being flood prone by the UBC watershed study, RPS was selected to prepare a Preliminary Engineering Report (PER) targeting flooding concerns along two Dry Branch Tributaries. The length of stream being studied totals 8,700 linear feet and involves a detailed flooding evaluation as well as a determination of viable channel conveyance and stability solutions. The various solution options being investigated by RPS will be developed with holistic watershed considerations in mind. A combination of solutions will target the reduction of flood overtoppings at road crossings, improvements to local storm sewers, retrofits for detention pond facilities, repairs for failing concrete drop structures, as well as needed conveyance and stability improvements within channel reaches. Channel stability improvements will include natural rock drop structures and riparian vegetation to stabilize ongoing bed incision and bank erosion within the project reaches. By utilizing the most appropriate natural channel design techniques within this highly urbanized creek, the creek will be restored and stabilized with local water quality enhanced. Following selection of the recommended solutions, RPS will then assist the City with the design and construction phases of the project improvements.

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