Influence of Land Use on the Water Quality of the Upper Mahaweli River: A Comparative Analysis in Dry and Wet Weather Conditions

Abstract

Understanding the relationship between land use and surface water quality is paramount for effective water management. A limited amount of research has been carried out focusing the effect of land use pattern and water quality of river basins in Sri Lanka, thus a study focused on the longest among all has not been traced in the literature up to data. As such this study has been carried out to investigate the, variations in water quality of Mahaweli River in relation to the different land use pattern. Water quality of the selected river stretch was examined for duration of four months and those were correlated with the land use data of watershed area of the river and the rainfall data of pertinent catchment. Study area was divided into three catchments based on their land uses. 15 water quality parameters at 10 sampling locations of study stretch were recorded. Analysis of land use data in three catchments revealed that there was a significant increment of urbanization from upper end to the lower end of the study area whereas agricultural and forest areas were prominent in the upper most catchments. Moreover, analysis portrayed that there was a significant impact from land use patterns on water quality. Ammonia-N, Turbidity, COD and BOD5 have observed to be dominant in urbanized catchments. Higher level of TSS has been observed with the increment of the agricultural/forest ratio. BOD5, EC, COD, Fecal coliform and TOC have been escalated with the increment of urban/forest ratio. Interestingly, most of the water quality parameters are not affected by the rainfall fluctuations in selected three catchments. Although the water quality parameters show significant variations with the impact of land use patterns, overall water quality classified as Water Quality Index (WQI) was similar for all three catchments.