Applicability of semi quantitative approach to assess the potential environmental risks for sustainable implementation of water supply schemes: a case study of Sri Lanka

Identification and quantification of environmental and socio-economic impact risks and effective monitoring of water projects are crucial for sustainable water resource management. Hence, the present study was conducted with the objectives of identifying potential environmental risks of different stages of the development of a new water supply scheme located in the wet zone of Sri Lanka, and categorizing identified impacts based on their significance. A rapid environmental assessment (REA) was followed to identify the upstream point source pollution and downstream water uses in the immediate catchment. Subsequently, a semi quantitative approach was conducted to screen the environmental, social, and economic risks concerning likelihood and sensitivity of the impact. Besides, an analysis of physico-chemical and biological parameters of water quality was conducted in the intake location. The semi quantitative method highlighted that low and medium risk with ecological impacts (50%), low risks towards sustainability of water source (75%), medium level constructional impacts (60%), and very high-level impacts at the operational stage were available (50%). A water quality monitoring program revealed that Escherichia coli count, total coliform bacterial count, and colour of the water were above the standard limits in the nearby freshwater source. In conclusion, a similar approach can be implemented worldwide as a reference to determine the potential socio-environmental consequences in water supply projects to minimize the adverse impacts. Through this study, sustainable mitigation measures were proposed accordingly to prevent the impacts and to strengthen the long-term viability of the new Rural Water Supply Scheme.