Harris County selected Costello to develop a Master Drainage Plan to evaluate known areas of flooding and develop drainage improvements within the M124-00-00 watershed. The project was comprised of two phases: Phase 1 consisted of channel improvements within the area between SH 249 and FM 2920 to mitigate the expansion of SH 249 (Tomball Tollway). Phase 2 consisted of the Master Drainage Plan, including developing a regional system between SH 249 and Harris County Improvement District # 17 which would alleviate local flooding and remove the majority of the watershed from the floodplain. In addition to providing flood protection, the new drainage system includes hiking trails along the banks to serve as a recreational amenity for the public. Costello coordinated with numerous government agencies with authority over the region, including Harris County, HCTRA, HCFCD, TXDOT, and the City of Tomball.

Due to large areas of overland sheet flow and poorly defined drainage paths, a two-dimensional (2D) model was utilized to simulate existing conditions drainage. The 2D model surface covered approximately 6 square miles and included 2 miles of earthen channel, which was modeled as 1D and coupled to the 2D surface. The model yields detailed animations of the complex flow patterns, enabling the identification of optimum placement of proposed improvements. Various proposed improvement alternatives, consisting of channel improvements and new detention facilities, were evaluated using 1D unsteady-flow computer models.