TxDOT IH 45 at North Shepherd
Designing Drainage Solutions for Freeway Safety Improvements within the Houston Floodplain
The intersection of IH 45 and North Shepherd Drive in Houston contained several dangerous merge and weave patterns caused by direct connector proximity. As a result, TxDOT undertook this project to replace the northbound and southbound direct connector bridges between Shepherd Drive and IH 45. In order to accommodate the new direct connectors, the project also included modifications to the IH 45 northbound frontage road, widening of the IH 45 mainlanes, and an added bridge over North Victory Drive and Little York Road.
KFA led the drainage design for the project, including the storm sewer design as well as detention, impervious cover, and floodplain mitigation. KFA obtained the as-built plans for the IH 45 and Shepherd Drive Interchange, IH 45 Freeway, and Shepherd Drive from TxDOT and used them in conjunction with survey and aerials to assess the existing drainage infrastructure located within the project limits. Then our team analyzed the existing storm sewer to determine the hydrologic runoff from the project area and designed the proposed storm sewer, utilizing and modifying the existing facilities where possible and ensuring that capacity, ponding and freeboard requirements were met. We determined the hydrologic impact of the project by comparing the proposed flow from the modified storm sewer systems to the flow from the existing systems and developed detention within the existing right-of-way.
The project is located within the 100-year floodplain for Little White Oak Bayou. KFA evaluated the impact to the floodplain by calculating the amount of fill being placed in the floodplain and proposed compensatory excavation for three areas in locations already being disturbed by the roadway and bridge construction activities to mitigate the new fill. The project area is also located within both the White Oak Bayou and the Greens Bayou watersheds. In the Greens Bayou watershed, two ramps were removed to allow for the northbound direct connector, resulting in a reduction of impervious cover. In order to accommodate the additional impervious cover within the White Oak Bayou watershed, KFA proposed three detention ponds.
The new direct connectors have removed the bottleneck and improved traffic flow. The drainage improvements designed by KFA mitigated the drainage impacts to existing conditions.