Assessments of seasonal groundwater recharge and discharge using environmental stable isotopes at Lower Muda River Basin, Malaysia

An accurate estimation of groundwater recharge is required to properly manage aquifers, especially for riverbank filtration method (RBF) purposes. The isotopes correlations and differences in different water bodies were studied to assess the sources of groundwater recharge and preliminary tools in understanding of the surface water and groundwater interactions in the Lower Muda River Basin. The environmental isotope and hydrochemical sampling results had emphasised that the area near Lower Muda River Basin had a connection with the river and was actively recharging the near-river shallow alluvial aquifer, via RBF method. Furthermore, the shallow groundwater that was close to Muda River from groundwater signatures had indicated the recharge of the shallow aquifer system by Muda River based on the plots along LMWL on a δ 2 H versus δ 18 O. The comparisons between like δ 2 H and δ 18 O isotopes in the rainwater revealed the variations in the rainfall amount and the 18 O-depleted water of those isotopes for wet season precipitation as compared to dry seasons. Furthermore, the groundwater δ 2 H and δ 18 O isotopes exhibited a slight deviation from the δ 2 H and δ 18 O isotopic meteoric water line in Lower Muda River. Therefore, in this basin, the groundwater could be a combination of river water and precipitation, which had led to the recharge of river water being more than the recharge of rainfall infiltration.