Calibration of Steady-State Seepage Simulations to Estimate Subsurface Seepage into an Artificial Wetland

The calibration of a two-dimensional, steady-state seepage model (FastSEEP/SEEP2D) to estimate the subsurface seepage into the Everglades Nutrient Removal (ENR) Project was performed. The ENR Project is a 1544 ha artificial wetland constructed by the South Florida Water Management District (SFWMD) to begin the process of removing nutrients (especially phosphorus) from agricultural drainage and stormwater runoff before entering the Everglades. A 8.2-km reach of the L-7 levee is the divide between the ENR Project and Water Conservation Area 1 (WCA-1), an impoundment area, which maintains consistently higher stages than the ENR Project throughout the year. Calibration of the model was conducted by comparing instantaneous surficial seepage flows (42 events) collected at the toe of the L-7 levee to model predictions. After selecting the most appropriate simulation (K values) from the calibration process, the model was run to obtain the 42 simulated values of subsurface seepage. These seepage flows and the average stages (WCA-1 and ENR Project) were used to obtain a regression equation (r²=0.962). This equation has been used to estimate the daily subsurface seepage flow component of the ENR Project water budget. For the first two years of operation of the project (August 1994 through August 1996), subsurface seepage was estimated to account for 7.8 percent of the total inflow. Estimation of the seepage components of the water budget, which is intrinsically related to the nutrient budget, is crucial to evaluate the efficiency of nutrient removal in treatment wetlands.