Seepage and the Lake Wimauma Water Budget
   Lake Wimauma, FL

Overview
The lake level of Lake Wimauma, located in southern Hillsborough County, Florida, has varied by 15 feet over the last few decades leaving the lake as two separate pools. As part of an effort to determine a minimum lake level, Water & Air developed water budgets for Lake Wimauma and nearby Carlton Lake. There was concern that geophysical anomalies beneath or near Lake Wimauma were providing a seepage pathway to the Floridan Aquifer whose head potential has been reduced by approximately 50 feet over the last half century. Historical limnological and geological literature and reports were reviewed before developing an approach to calculate and/or measure, in monthly increments, the following water budget components: precipitation, rainfall runoff, overflow from the East Pool to the West Pool, near-shore seepage, "far-shore" seepage (vertical leakage), evapotranspiration, change in lake volume, and residual.

Details

• Datalogging pressure sensors at both pools of Lake Wimauma and in Carlton Lake monitored rainfall, lake level and barometric pressure to quantify individual rainfall events, lake stage changes, runoff inflows, overflow between pools, and change in lake volume.
• Seventeen near-shore seepage meter stations in the three water bodies monitored seepage inflows and outflows and identified a substantial area of the West Pool where groundwater recharge was occurring.
• Eight "far-shore" seepage meters in the West Pool identified areas with substantial groundwater recharge.
• Bathymetric measurements and sediment type mapping was used to refine seepage meter placement.
• Seepage and bathymetric measurements were used to locate geophysical transects for electrical resistivity and seismic reflection measurements.
• Floridan wells were identified to interpolate hydrostatic head potential at each lake.
• Shallow piezometers were installed around and within the lakes and potentiometric maps were created to help interpret groundwater flow directions.

Results
The water budget for Carlton Lake yield a difference between the inflows and the outflows of 0.90 inches per year. The East Pool seepage was calculated to contribute +13.7 inches, or 19.7% of the total annual inflow. In the West Pool, seepage near the shore was calculated to contribute +5.85 inches, or 8.9% of the total inflow, while seepage further from shore drained the pool of approximately -10.86 inches, or 16.3% of the total outflow. In-lake and terrestrial piezometers indicated lower head potentials near areas of greatest seepage from the West Pool.