WATER BALANCE ANALYSIS OF A FLOODPLAIN SYSTEM: CONGAREE NATIONAL PARK

Congaree National Park (CNP) is a floodplain forest wetland system in central South Carolina which experiences regular flooding from overland flow due to high stage events (mainly from the Congaree River) as well as saturation-excess (groundwater) flooding due to longer-term water surplus conditions. The goal of this study was to estimate the water balance for a section of this floodplain using a mixed-method approach. Local weather data from CNP were used in the Priestley-Taylor potential evaporation (PET) model to calculate this important factor of the water balance for this region. Estimates of average PET was 3.3 mm/day (ranging between 1.7 and 4.8 mm/day). Groundwater conditions were simulated using the U.S. Geological Survey’s MODFLOW for a 165-hectare section centered around the Congaree Observation Well Network. Results show an average annual groundwater recharge rate of 0.11 mm/day. By using precipitation and Priestley-Taylor PET data and a water balance approach we estimated the average AET was 3.0 mm/day (1.5 – 3.2 mm/day). In this presentation we will discuss approaches to upscale recharge estimates to larger areas of the floodplain using geostatistical methods such as cokriging (e.g., extending estimates beyond the model domain based on the relationship between recharge and factors such as topography and hydraulic conductivity), and comparing annual average precipitation data and PET estimates for the region. We will also discuss the implications for predicting water availability for this area and similar river basins.