System Dynamics Based Model for the Nachchaduwa Reservoir in the Malwathu Oya Basin, Sri Lanka

Though Sri Lanka is a water rich country where many water resources development projects have been implemented, the country still very often faces many issues due to water scarcity. By improving the management of existing water resources development projects such issues could be addressed. The irrigation area coming under the Nachchaduwa Reservoir Scheme in the Malwathu Oya Basin has encountered severe water scarcities in the recent past. This paper presents a system dynamics based simulation model that will help in making decisions for managing the Nachchaduwa Reservoir for fulfilling the water requirements of its irrigation area. The model was developed using system dynamics concepts and the software used was Vensim Professional. The advantage of system dynamics modelling is its ability to model many different sectors such as water quantity, population, agriculture and economy using one single model making it possible to look at all sectors using the same model . The model developed for the Nachchaduwa Reservoir System comprised of the above sectors and was used to investigate several optional operation patterns of the system. Four different operational patterns were considered based on crop types and cropping areas. Initially, the developed model was tested for its applicability and thereafter it was used to determine the most suitable cropping pattern. The results indicate that the patterns consisting of 100% paddy during the Maha Season and 50% paddy and 50% maize during the Yala Season as the most suitable cropping patterns for the two seasons. The model also showed that the temporary increase in the population by the pilgrims and tourists visiting the area during festive seasons affects the amount of water available for crops.