Evaluation of Facilities Alternatives for Spreading Stormwater Flows Overland to Promote Large Scale Wetlands Rehabilitation

In the context of a major Florida wetlands restoration project, it was necessary to distribute flows over a land area on a continuing basis in a way that promoted recovery of overland flows and recharge to a more natural condition. Complicating this requirement was the limited available head to drive hydraulic processes, because of the very flat coastal Florida landscape, and the need to deal with all levels of flow from major flood events down to gentle summer storms, all in the complete absence of defined downstream drainage works. A substantial literature review was conducted to evaluate prior approaches to this problem. Parallels were discovered, principally in the agricultural literature, but closely similar projects were not encountered. Solutions considered ranged from concrete hydraulic structures with energy dissipation and overflow weir systems, to simple trenches orthogonal to the landform gradients. It was concluded that although they might be effective, concrete structural options were costly, were prone to excessive head losses, and did not lend themselves to integration into the natural landscape. Overflow trenches were attractive in their simplicity, but raised the specter of eventual cut-down and development of preferential flow paths rather than development of broad wetland areas. The preferred solution consisted of long spreader berms with numerous controlled overflow points. This option not only integrates nicely with the prevailing landscape, but can be adapted in the long term as management of the system is adjusted to meet the needs of the evolving ecosystem during its recovery period.