Groundwater QUALITY Assessment: Application of Irrigation Water Quality Index (IWQI) in Malwathu OYA Cascade-I, Sri Lanka
Water scarcity is one of the most prominent constraint in dry zone of Sri Lanka and as a convenient source, extraction of groundwater through large diameter open dug wells named “agro-wells” were introduced. Agro-wells are extensively used for irrigation purposes and deterioration of water quality is visible. It is necessary to combine all related parameters together appropriately rather than focusing on a single isolated parameter, to manage this valuable resource sustainably. Twenty groundwater samples were collected to determine its suitability for irrigation purposes in MalwathuOya cascade-I, Sri Lanka and analyzed for physical and chemical parameters. Irrigation water quality index (IWQI) was used for this purpose. Empirical Bayesian kriging (EBK) available in GIS was used to show the spatial distribution of water quality parameters. Based on the salinity hazard, major portion of the study area falls under slight to moderate restriction for irrigation in both seasons. Nitrate nitrogen concentration was higher in Maha season compared to Yala season due to leaching of excess fertilizer to the shallow groundwater. Based on SAR all the wells were suitable for irrigation with no danger of exchangeable sodium. Results of IWQI showed that the general groundwater quality in the study area is found to be mostly suitable for irrigation.
Keywords - Agro-wells, Empirical Bayesian kriging, IWQI, Tank cascade system.