Modeling water allocation options in Deduru Oya reservoir system, Sri Lanka

Abstract

Water balance under different management scenarios was tested in Deduru Oya reservoir project system, Sri Lanka with focus on Left Bank canal system to address agricultural, energy, and environmental water deficits in all seasons. A conceptual rainfall-runoff model, SimHyd, was employed for modeling discharge into ancient tanks. CropWat model enabled estimation of irrigation water requirement for rice crops, the main agricultural water demand. Water Evaluation And Planning (WEAP) model was applied for testing deficits between water supply and demand systems. Graphs of coverage and unmet water demands pointed out that most of the tanks are not able to meet two-season irrigation water requirements. Water shortages occurred in the months of March, May, June, and September. In dry climatic year, tanks and reservoir storages together may not be well enough to meet September water demands if operated conventionally (i.e., farmers are free to use tank water as they want). Results of water allocation modeling pointed out that there will be no water shortages if farmers are convinced to retain water of about 40% of tank inflows for the use in September.