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ISMAR7 Abstract
Combining the improved soil moisture balance and water level fluctuation methods to estimate recharge: A case study from limestone aquifer
Thushyanthy Mikunthan
Department of Agric. Engineering
Faculty of Agriculture
University of Jaffna
Quantification of the rate of groundwater recharge is a basic pre-requisite for efficient groundwater resource management. It is particularly important in regions with large demands for groundwater supplies as Jaffna peninsula, Sri Lanka where such resources are the key factor for life and to economic development. In recent years, increasing demand for groundwater has raised concerns about resource sustainability and has highlighted the need for reliable estimates of groundwater recharge. Groundwater is a renewable resource, hence it is not only sufficient to assess the potential of groundwater but it is also necessary to manage it efficiently, so that long term benefits can be achieved. A relatively simple and practical approach for calculating groundwater resources in dry zone environment with relatively shallow water table in limestone aquifer is estimated and measured by using improved soil moisture balance method (SAMBA) and water level fluctuation method respectively for the period from January 2007 to April 2009. Water level fluctuation was measured on daily basis from sixty wells and analyzed by two approaches; graphical extrapolation and direct calculation by using RISE programme approach. Results reveled that the SAMBA model is a reliable approach for potential recharge estimation in a wide variety of situation. Direct check can be made of the recharge estimates, results from soil moisture balance calculations are compared with well hydrograph. Groundwater recharge rates of the limestone aquifer range from 23% to 25% of annual rainfall as determined SAMBA model for 2007 and 2008 whereas by WTF it was 19% and 27% of annual rainfall. There is an acceptable agreement in identified main period of recharge by both methods. But graphical extrapolation mostly agrees with result of the SAMBA. Hence the model SAMBA and graphical expression of water table fluctuation could be a useful tool to estimate the recharge in limestone aquifer.
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