The Crane Strand Drainage System was identified by several sources as a significant contributor of pollutants to the Little Econlockhatchee River. The primary objective of this project was to provide pollutant removal for the existing drainage system. SAI developed and evaluated 15 conceptual designs that included wet detention, alum injection, and/or end-of-pipe treatment structures as well as multiple pond locations. The selected design involved the construction of a 2.6-acre in-line regional stormwater facility on County-owned property adjacent to the Crane Strand Canal. The wet detention pond included a 100-ft "duck-billed" weir, dual 12'x4' concrete box culverts, and a baffle box with a floating debris basket to accommodate high flow conditions.
The project required stormwater modeling for a 5.7-square mile study area, pollutant load estimates, regional stormwater facility design, construction document preparation, and regulatory permitting. At the request of the St. Johns Water Management District, SAI developed a methodology to determine estimated pollutant removal efficiencies based on residence time in the facility, rainfall frequency information, and hydrodynamic modeling results. This methodology was needed because the pond area and volume were significantly limited relative to the treatment area and assumed levels of treatment based on presumptive criteria alone could not be used in the calculations. The design also required careful attention to flood stages since the area already had flooding concerns.
SAI's final design not only provided a water quality improvements benefit, but also reduced flood stages in the watershed and removed an estimated 9 residential structures from the 100-year floodplain. In addition to the design efforts, SAI was instrumental in helping the client secure $1.3 million in grant funding for the project.