Estimation of groundwater recharge in South Florida using drainage lysimeters
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abstract
South Florida's high hydraulic conductivities sandy soils, shallow water table conditions, and high annual rainfall result in high surface-ground water interactions. Such conditions are conducive to high percolation and groundwater evaporation rates, which make annual percolation difficult to quantify. The percolating water Is a major source of recharge for the surficial aquifer. Quantification of the annual recharge volume is essential in regional water resources management. Water balance is one of the most reliable methods for recharge calculations. An experiment was conducted in south Florida using four drainage lysimeters to estimate seasonal and annual recharge to the shallow water table over two years (2004-2005) from vegetable fields. Four large drainage lysimeters (4.87m 3.65m 1.37m) were instrumented to measure inflow (irrigation and rainfall), outflow (drainage and runoff), and storage (soil moisture). Weather data were also collected. Two lysimeters were irrigated using the seepage irrigation system while the other two lysimeters were irrigated using the drip system. Ground water recharge was calculated using water table change and soil moisture measurements. Results showed that the average annual recharge constituted 44% (534 mm) of the total rainfall in row crops production areas in south Florida. Recharge was found to be higher in drip irrigated systems. This is mainly because of a deeper water table in drip compared to the seepage system. Recharge was found to be affected by groundwater depth, rainfall volume, seasonal weather, and soil and crop characteristics.
