Analyzing the seasonal variation of groundwater characteristics in the Attanagalu Oya basin

Abstract

Gampaha district which has the second largest population in the country consists of many industrial establishments and residential areas. Attanagalu Oya Basin which almost entirely the Gampaha district is a major hydrologic feature in determining the seasonal variations of groundwater characteristics in the region. In this study, the groundwater characteristics in the Attanagalu Oya Basin analyzed both quantitatively and qualitatively to identify variations in the pre and post monsoon periods. The qualitative parameters such as pH, conductance, turbidity, calcium, magnesium, nitrate, phosphorous, ferrous, and heavy metal concentrations were analyzed for samples taken throughout the entire basin for the two time periods: pre and post monsoons. The groundwater quantity variations were observed through data loggers and field surveys of water wells. These recorded values were used to model the groundwater resources in the region using two numerical models, MODFLOW by USGS and a self-written Fortran code. The qualitative and quantitative variations were then analyzed spatially and temporally to correlate with the upstream to downstream flow and the monsoonal recharge. The possible reasons for the observed trends and variations were also studied to provide recommendations for the sustainable management of the groundwater resources in the Attanagalu Oya Basin.