Enhancing of drinking water source for the city of Tangalle

The Tangalle town is located on the Southern coastal belt of Sri Lanka and the source of drinking water to the Tangalle town is the Kirama Oya. Due to rapid expansion of the town the project operates at 25 % of its capacity. In addition the projected demand of 15,000 cu.m.per day is required in 2025. Due to competitive use of water for irrigation during the dry weather periods, it is conceptualized to store back water of Kirama Oya during floods in a lake. The floods which normally occur with the monsoonal rains are expected to fill up the lake. Apart from the empirical knowledge available regarding the flooding of the Kirama Oya , there was no detailed hydrological study. This paper describes the application of NAM hydrological model and HEC_RAS hydrodynamic model to understand the process of flooding, its frequency of occurrence and any implication of impounding water in Nawayalawila on the existing environment.