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Estimation of Lateral Subsurface Flow in Lateritic Formations Using Well Hydrograph Analysis

Udayakumar, G., Mayya, S.G., Ojoawo, Samson O.
Aquatic Procedia 2015 v.4 pp. 1062-1069
aquifers, coasts, dry season, equations, groundwater, hydrograph, monsoon season, permeability, porosity, rain, subsurface flow, subwatersheds, summer, wells, India
The lateritic formations in west coast of India face a unique problem. In spite of good recharge in unconfined aquifer during monsoon every year, these aquifers drain very quickly in summer season. This is mainly due to the high porosity and permeability of these formations. Proper estimation of lateral subsurface flow from these formations is necessary for sustainable water management. This component is estimated by considering groundwater balance equation. Well hydrograph analysis has been carried out to obtain the gross and net recharge components. 42 open wells of varying diameters and depths spread over the entire microwatershed have been identified for the purpose. A recession equation is developed to predict the water level below ground level in the well at any particular time period of the dry season. Recession curve corresponding to dry periods is considered in obtaining specific yield (Sy)of the formation. The recession flow analysis carried out for the wells show an average value of recession constant for the shallow wells as 0.003 and for deep wells as 0.001. The specific yield determined from recession curves vary from 0.013 to 0.036. The average subsurface flow (SSF) from the microwatershed is found to be 0.09 m /year which is equal to 2.78% of the total annual rainfall. The lateral subsurface flow is estimated as a residue of groundwater balance equation.