Estimating recharge based on long-term groundwater table fluctuation monitoring in a shallow aquifer of Malaysian tropical rainforest catchment

A practical and reliable approach was applied to investigate the groundwater dynamics and obtain natural direct recharge based on the time series of water table fluctuation in moderately flat coastal area with a shallow water table and tropical rainforest weather. Drainage rate was about 0.034 m/day in the study area as estimated by falling groundwater table in period of no rainfall and specific yield values ranged between 0.11 and 0.23 by calculating depth-dependent specific yield based on soil water storage for layering soils. The method was applied to the monthly data of shallow aquifer at eight field sites in north Kelantan river catchment in the period of 1991-2011. The cross-correlation and partial cross-correlation reveal the acceptable correlation between the water table fluctuation and the rainfall data assuming the time lag from precipitation to water table response is negligible due to shallow water table. Recharge rates vary with the field sites and mainly depend on soil type and rainfall rather than surface geology. Although computer simulation (with MRCR code) was implemented with limited data (two series), still results are just slightly greater than the field data which indicated the method successfully employed and can be applied in areas with similar conditions in future.