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Gridded Surface Subsurface Hydrologic Analysis Modeling for Analysis of Flood Design Features at the Picayune Strand Restoration Project

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Technical Report,01 Jan 2013,01 Aug 2016

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Coastal and Hydraulics Laboratory, U.S. Army Engineer Research and Development Center Vicksburg,

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The Picayune Strand Restoration Project is one of many components of the Comprehensive Everglades Restoration Project CERP intended to restorenearly 700 hectares of a failed residential development in southwestern Collier County, FL, to its predevelopment wetland conditions. A detailed analysis was performed to derive a restoration plan that will achieve this goal. As required by the Water Resources Development Act WRDA 2000,the U.S. Army Corps of Engineers USACE is required to ensure that no component of CERP results in an effective taking of land by adversely impacting the level of flood protection of adjacent landowners. To ensure the current level of flood protection is maintained, a hydrologic model was developed to assess the potential for flooding and to refine the proposed flood mitigation features. The USACE physically based Gridded Surface Subsurface Hydrologic Analysis GSSHA model was selected for this effort. The GSSHA model simulates fully coupled rainfall distribution, extraction, retention, overland flow, and one-dimensional channel flow. Models of varying resolution were developed from existing and proposed design data and were initially populated with parameter values from a previous hydrodynamic modeling effort. Parameters were then tuned to observed stage and flow data using the Secant Levenberg-Marquardt method, a nonlinear least squares minimization computer-based local search method. The calibrated model is capable of reproducing canal flows, canal stages, and overland stages with very high Nash Sutcliffe Forecast Efficiencies, generally 0.9 or higher. Subsequent uncertainty analysis allowed water stages to be estimated with 95 certainty. Modeling and uncertainty analysis results allowed for refinement of the proposed flood mitigation features.

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