Stormwater Master Plan

10-year and 100-year floodplain boundaries delineated with HEC-GeoRAS.

Working as a subconsultant to the Wallace Group, PBS&J helped develop a stormwater master plan for the City of Waco, Texas to address drainage issues. The city's focus included addressing drainage issues in an 80-square-mile area comprising 15 basins that drain into the Bosque and Brazos Rivers.

During the project’s first phase, PBS&J worked with the city to refine existing GIS drainage databases, update drainage ordinances and policies, and selection of software tools. The second phase of the study included execution of a detailed modeling program and recommendations for necessary capital improvements.

A pilot program was established on a single basin to develop a procedural template for the rest of the study. New hydrologic and hydraulic models were created by supplementing existing model information with new aerial topography and data obtained during site visits. These models were used to analyze watershed conditions for a wide range of storm events and develop proposed solutions. Additionally, a combination of GIS pre- and post-processing tools was used to automate model creation and floodplain mapping. Software included PrePro2002 (a precursor to HEC-GeoHMS for ArcGIS), HEC-GeoRAS, HEC-HMS, and HEC-RAS, and StormCAD. Problem areas were identified and recommendations for a CIP program were prepared and summarized.

Applying the procedures established – and lessons learned – during the pilot, 14 remaining basins were analyzed. Recommended CIP projects were combined into a decision matrix that prioritized the proposed projects throughout the city. Lastly, PBS&J will train city staff in the procedures and software used during the study, focusing on the GIS geodatabase and hydrologic and hydraulic modeling, allowing them to update the information as needed.