Rosillo Creek RSWF SC-15

Bexar County, Texas

IDS was selected to perform engineering services to remove several hundred single-family residential homes from the 100-year floodplain of a tributary of Rosillo Creek. This tributary was located within the City of Kirby between Ackerman Road and FM 78. The initial concept focused on a detention basin as the solution.

IDS prepared a preliminary engineering report (PER) to evaluate the detention basin option for feasibility as well as to develop additional options and evaluate the feasibility of each. The report analyzed three options that included detention upstream of the tributary, detention along the tributary, and increased capacity of the channel and culverts. The study started with reviews of the recently concluded DFIRM hydrology and hydraulic models. The contributing watershed was approximately three square miles and the tributary was approximately 6,500 LF. The HEC-HMS model required modifications to more accurately reflect sub-watersheds. Additional modifications were made to the HEC-HMS model to include the potential detention sites. The HEC-RAS model was modified to reflect proposed channel and culvert modifications.

Our ultimate recommendation in the PER was that the detention basin option be replaced by the reconstruction of the channel and road crossings to increase the conveyance capacity. The two detention options were not recommended due to their ineffectiveness to reduce the water surface and inability to acquire enough land. The results of the PER were submitted and accepted by the program and the project proceeded forward into detailed design.


The design phase consisted of engineering a two-phase project. The first phase consisted of the design of two bridges while the second included deepening the channel and replacing three more street crossings. Of the five road crossings, three were designed to replace box culverts with clear span bridges while still maintaining two-way traffic flow. The project also included coordinating with the US Army Corps of Engineers to obtain an individual permit and mitigate impacts on existing wetlands. The new construction will take place primarily within existing right-of-ways/easements and require minimal easement acquisition.