RRP provided engineering services for the preparation of drainage reports for three H&H Drainage Segments due to roadway improvements to the Sam Houston Tollway. Project limits span from IH 45 N to SH 225 (approximately 62 miles) and cross Greens Bayou Watershed, White Oak Bayou Watershed, and Buffalo Bayou Watershed. The drainage study focus was to assess potential mitigation needs due to any potentially increased flows from Sam Houston Tollway operational improvements.

Drainage analysis included evaluation of the current Sam Houston Tollway drainage system based on Atlas 14 rainfall data, assessing existing cross drainage structures, and performing an evaluation to determine if the existing roadway and drainage system meets the current TxDOT and Harris County Flood Control District (HCFCD) standards. For the proposed condition, drainage analysis included evaluation of storm sewer trunklines, channel drainage component sizes, assessment of bridge structures (including scour analysis), assessment of drainage crossing structures, and determination of mitigation needs for abutting properties. The drainage impact study and H&H drainage study include applicable hydrologic and hydraulic models prepared with XP-SWMM. The drainage report is a comprehensive compilation of drainage area maps, drainage outfall descriptions, and recommendations for mitigation of impacts. Plans will advance development of hydraulic data sheets and drainage area maps for bridges, bridge-class culvert crossings, and non-bridge-class culverts.