A Master Drainage Plan was prepared for Baybrook Municipal Utility District Number 1 (BMUD 1) to provide a comprehensive drainage evaluation of the existing facilities around the Baybrook Mall, located in southern Houston. As part of the evaluation, the existing drainage system was hydraulically modeled to identify inadequate capacity areas within channels and detention ponds. The original system was designed utilizing data and criteria available in the 1970s, which has changed substantially compared to current regulations.
Costello provided a topographic survey of the existing trunk storm sewer network, channels, detention basins, and key hydraulic structures. As final recommendations and design work was completed, our survey team provided legal descriptions for use in right-of-way dedications and easements to the Harris County Flood Control District.
Several area improvements were proposed to bring the existing system into compliance with current regulations and provide sufficient capacity for future development. These improvements included expanding existing detention basin capacities, modifying outfall structures, and modifying roadway crossings along Tributary Channel A111-00-00. The proposed system provides sufficient detention and floodplain mitigation volume to serve 560-acres of future commercial development located within BMUD 1’s jurisdiction. The analysis utilized XP SWMM (a dynamic modeling software), as well as HEC-HMS (hydrology) and HEC-RAS (hydraulic) models obtained from FEMA.

The analysis was completed for the 2-year, 10-year, and 100-year 24-hour storm events. The 2-year evaluation helped ensure that the existing area storm sewers could provide the same or better level of service after improvements are completed. Geographic Information System (GIS) mapping and data management were utilized in hydraulic modeling and provided a visual record of results through mapping.

To more effectively support development, the overall project’s construction was completed in three phases to allow improvements to be constructed as needed. In-line mitigation was proposed to reduce the land required for detention by expanding the existing A111-00-00 channel. The expansion was proposed so the existing, ordinary high-water mark will be left undisturbed, which helped facilitate the approval of environmental permitting and construction phasing. Coordination with various agencies included Harris County CIP, Harris County Flood Control District, City of Houston, and the Texas Department of Transportation. Construction phase services were also provided through the closeout of construction.