Potential of Water Balance Modelling with Surface Water Pollution Considerations to Manage Ungauged Watersheds with an Emphasis on Multi User Concepts – Demonstrating an Application at a Watershed in Dampe, Sri Lanka

Abstract

Practicing integrated water resources management (IWRM) for sustainability is vital when there is multi user competition for the finite fresh water resources. In order to facilitate early decision making, it is necessary to evaluate ungauged small watersheds with simple, easy to apply but quantitative tools. This paper demonstrates the possibility of successfully applying the multiuser concept, the finite nature of water and system water balance, as a mean to overcome the surface water pollution in Dampe watershed (0.62km2), Sri Lanka. Since this watershed is ungauged, field visits, gauged data from the locality, estimates from available literature were used for a rational application of water balance to evaluate solutions for surface water pollution. The watershed runoff was calculated using a two parameter water balance model which enabled soil moisture accounting. The monthly water balance model for Dampe watershed which included multi sectoral water uses, the surface water quantity and quality at each key stream node for each sub catchment enabled the analysis of several scenarios. Remedial measures to overcome the problem and sustainable methods to preserve water for the future generation are proposed.