US 11 from Cayten Street to Lakeshore Drive

The Mississippi Department of Transportation (MDOT) proposed a plan to widen U.S. Highway 11 between Cayten Street and Lakeshore Drive from a 3-lane section to a 4-lane divided boulevard through Picayune in Pearl River County, MS. Mendrop Engineering Services, LLC (Mendrop) was retained by MDOT to perform a hydrologic and hydraulic analysis of the proposed storm drainage system for the roadway widening. The study included the development of a hydraulic storm sewer model of the storm drainage system as currently designed in order to evaluate and document the hydraulics of the system.

Design criteria specified in the MDOT 2001 Roadway Design Manual was followed in order to develop the necessary hydrology for the storm drainage system. The post-project hydrologic parameters were modeled within the Hydraflow Storm Sewer System to develop peak discharges from the proposed storm sewer system. GeoPak Drainage by Bentley was utilized to develop a storm sewer network model to verify and confirm the results from the Hydraflow Storm Sewer Model. GeoHEC-RAS was used to develop a geo-referenced HEC-RAS model. A pre-project and post-project model was developed to evaluate the effects of pre- and post-project discharges. Upon analysis of the resulting data, Mendrop designed and evaluated several design alternatives to mitigate the increase in peak discharges and water surface elevations produced by the post-project storm drain system.

Additionally, Mendrop used SewerGEMS to model the proposed storm sewer network and identify areas where the hydraulic grade line exceeded the top of curb elevation along pipe segments within the network. Mendrop also utilized the model to identify pipe segments where the slope needed to be reviewed to maintain self-cleaning velocities and where inlet spacing may need to be adjusted to reduce the spread width.