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Interaction of Groundwater with Lake Panasoffkee, West-Central Florida

Project Chief: Scott McBride
Cooperator: Southwest Florida Water Management District
Period of Project: October 2005 – September 2009

Problem Statement

Figure 1. Location of the Lake Panasoffkee study area in west-central Florida.

Water managers and local residents have expressed concern that population increases in the Withlacoochee River basin, along with the ensuing development, could impact groundwater resources. Increasing competition for the area’s groundwater resources and changing water use patterns have strained the groundwater resources. Future well fields and urban areas adjacent to the lake could affect groundwater and surface-water levels and quality, potentially impacting wetlands and making the Withlacoochee River more susceptible to flooding. As demands for water in southwest Florida increase, more information is needed to effectively develop and manage the Withlacoochee River watershed.

A better understanding of the interaction between groundwater and surface waters, and the magnitudes of evaporation and groundwater seepage, and how these relate to Lake Panasoffkee and the Withlacoochee River (fig. 1), is essential to water managers. Previous and on-going studies have shown that a strong hydraulic connection exists between surface water and groundwater in the area, but data on the water budget and dynamics of the hydraulic connection between Lake Panasoffkee and the Upper Floridan aquifer was scarce. Evaporation and groundwater seepage represent important but poorly quantified water-budget components in the area and are of critical importance in hydrologic analyses of the area’s water resources. Collection of evaporation and groundwater seepage data is needed for a more comprehensive understanding of both groundwater and surface-water systems and to develop effective resource management.

Objectives

1) Assess the hydraulic connection of surface water in Lake Panasoffkee with groundwater in the Upper Floridan aquifer 2) Refine the water budget of Lake Panasoffkee by incorporating onsite estimates of evaporation and groundwater seepage

The connection between the surface water and groundwater was assessed by: (1) determination of existing groundwater conditions with respect to directions and rates of lake/aquifer interflow; (2) determination of seasonal and long-term ranges in water-level fluctuations and volume of inflows and outflows; (3) analysis of synoptic spring discharge measurements during low- and high-baseflow of lake inflows and outflows; (4) analysis of isotopic and geochemical data; (5) hydraulic analyses of groundwater flow in regions adjacent to the lake; and (6) refinement of evaporation and groundwater components of the water budget.

Figure 2. Summary of monthly water budget data for Lake Panasoffkee during water years 2007-2008.

Approach

The assessment of the hydraulic connection between groundwater and Lake Panasoffkee required an extensive data collection and analysis program involving groundwater, surface water, quality of water, rainfall, evaporation, recharge, and land use information. Two of the hydrologic fluxes used in calculating the water budget (groundwater fluxes and evaporation) were improved with on-site data collection (fig. 2). The general plan consisted of conducting spring runs, deploying manual seepage meters (to measure flow directly), characterizing water quality and hydrogeology, collecting groundwater and surface-water levels, and conducting a hydraulic analysis of the groundwater flow system. Seismic-reflection profiling was conducted to identify geologic units and solution features. Piezometers driven into the lake shore were used to measure vertical gradients between the lake and the underlying aquifer system.

Results

The project provided a comprehensive evaluation of the hydrologic conditions in the study area and surrounding areas and an evaluation of the hydraulic connection between Lake Panasoffkee and the groundwater system.

Information Product

McBride, W.S., Bellino, J.C., and Swancar, Amy, 2011, Hydrology, water budget, and water chemistry of Lake Panasoffkee, west-central Florida: U.S. Geological Survey Scientific Investigations Report 2010-5237, 96 p.