H&h Modeling For Wetland Restoration In Florida

Tetra Tech was contracted by the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS) to prepare and design wetlands reserve plan of operations (WRPOs) for several wetlands reserve easement sites in Florida under Easement Restoration Agreements with NRCS. These properties were historically marsh systems that were converted for agricultural purposes. The goal of the WRPOs was to determine structural and ecological measures that can be implemented to restore wetland function and historical site conditions to the extent practicable. The wetland function is restored by altering the existing drainage pattern to retain the water onsite without creating any offsite impact. Offsite is considered as all contributing drainage areas upstream of the project area.

To achieve this goal, Tetra Tech performed hydrologic and hydraulic modeling scenarios (short-term and long-term) to study the existing and anticipated wetland condition as a support tool for the WRPO development. Each wetland has unique features in terms of surface hydrology (i.e., rainfall, evapotranspiration, topography, area, soil, vegetation pattern, water quantity and quality etc.) and it is challenging to address these features in the model development. Also, groundwater plays a significant role in the wetland function over the long-term as development of the wetland vegetation vastly depends on groundwater, which fluctuates seasonally in Florida.

Recognizing this fact, Tetra Tech developed a two-dimensional Interconnected Channel and Pond Routing version 4 (ICPRv4) model that includes surface water and groundwater interactions. ICPRv4 includes a fully integrated one-dimensional/two-dimensional surface water module coupled with a two-dimensional groundwater module with an emphasis on interactions between surficial aquifer systems and surface waterbodies. The model was used to identify the extents of inundation at specific water surface elevations, provide water depth temporal variations at the sites for the required storm events, and identify vegetation habitats based on varying water surface elevations. The model results provided the expected water levels onsite after restoration elements are implemented, which were used to determine the associated vegetation communities that could be present post-restoration.

The model was simulated for several rainfall scenarios to provide our engineers and biologists with the information needed to find the optimal solution and design for the wetland restoration. The engineering solutions included measures such as weirs, embankments, ditches, and ditch blocks, which were coupled with ecological practices to restore the sites.