Due to the increase in land development and inadequate stormwater conveyance, the W-15 Drainage Basin in St. Tammany Parish, Louisiana experiences significant flooding. Beginning in 2011, DDG developed a comprehensive plan for drainage improvements. The project consisted of preparing a HEC-RAS and HEC-HMS for a project area of 35-square miles that encompasses three separate but interconnected basins including W-15 Canal, W-14 Canal, and Gum Bayou Basin. Utilizing previous model data from the Southeast Louisiana Urban Flood Control Project (SELA) as well as newly acquired topographic and bathymetric data, models were developed to understand existing flooding conditions and to evaluate various alternatives for improving flood conveyance and storage. A total of 27 different alternatives were evaluated to determine the most economical solution to alleviate the existing flooding problems in different parts of the basin. A Benefit Cost Analysis (BCA) was prepared for FEMA to facilitate the award of Hazard Mitigation Grant Program (HMGP) funds.
The recommended project included the construction of a 324-acre regional detention pond and cleaning and widening of approximately 3 miles of the W-15 Canal. This project accomplishes two objectives: reducing peak runoff to the W-15 Canal downstream of the Tenet Pond and increasing the conveyance capacity of the W-15 Canal. These two project elements effectively reduce the water surface elevations along the W-15 Canal thereby reducing impacts to structures throughout the W-15 Basin. DDG provided engineering services to St. Tammany Parish that included engineering design, permitting, preparation of bid documents and construction inspection.