Hydrogeological evaluation of a watershed with mining activities: Case study of Salaulim reservoir, Goa, India

Abstract

Open-cast mining is an important economic sector in Goa, India. It often requires large quantities of groundwater to be pumped out. This can lead to water stress conditions if the quantity of groundwater extracted surpasses the total recharge. To examine this, hydrogeological investigations were carried out in the catchment of Salaulim reservoir which had mining activities. The watershed was delineated into three sub-watersheds (Guleli, Kumbhari and Curpem) covering a total area of 180 km2 and a reservoir area of 29 kin. During the study period (2011-12), 4 working, 22 non-working mines and 5 laterite quarries were recorded. The ground water level data was collected for 3 seasons. The average water level fluctuation (between pre- and post-monsoon) was found to be 1.06, 0.97 and 1.14 m for the wells in the above-mentioned watersheds respectively. Flow net maps were prepared to study the flow path of the groundwater and understand the potential pathway of contaminant. Field experiments were conducted to estimate aquifer parameters and monitor water quality. The sectoral groundwater demand, draft and recharge were calculated and used to estimate total groundwater availability which was 192 hectare per annum. The stage of groundwater development was 38.8 percent which is classified as 'Safe' as per the norms. This stage is based on the draft from only 4 active mines and would definitely aggravate if more mines are allowed in the vicinity of the reservoir. Well hydrographs based on 5 five years secondary data indicate that there was no decrease in groundwater levels in the study area. However, a decreasing trend was observed in a well which lies close to the watershed. Taking this as an indication, judicious withdrawal of groundwater in future is warranted.