Determination of reservoir protection zones in watersheds by a physically based approach

Watershed management and catchment scale studies have become increasingly important in determining the impact of human development on water quality both within the watershed as well as that of receiving waters. One way of preventing water bodies from being polluted by many different kinds of pollutants is to design protection zones around those water bodies. The determination of reservoir protection zones is a significant issue in many parts of the world. The width of the protected area is one of the basic factors to be considered when setting up and managing the zones.Today, most countries face difficulties in accomplishing sufficient reservoir protection strategy due to either the shortcomings in their central and local legislations or to the presence of too many regulations. The restrictions applied by authorities as ruled by legislations have direct impacts on the social and economical activities of the population residing in the basin. Besides, a protection strategy based on a fixed zoning system somehow fails to detect the variable protection needs when applied invariably for all basins, even of varying sizes and with distinct drainage characteristics. The approach employed in this study provides a comparably practical methodology for deciding upon an optimum protection distance in a watershed. Its most distinctive outcome is the feasibility of defining protection zones of variable distances for the applications in different catchments, but securing all assessments to be based on a single scientific reasoning. It basically considers a number of individual analytical components including the average times it takes water to travel within protection zones down to reservoir, the potential diffuse pollution risks originating from certain types of land uses, the potential role of sedimentation in a catchment to trigger pollution transfer and amplify pollution impacts on reservoir systems, and the utility of land as a resource.