Modeling water allocation options in Deduru Oya reservoir system, Sri Lanka
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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.
KeywordsIrrigation water requirement Water evaluation and planning Rainfall-runoff modeling Food security Integrated water resources management
This study was carried under CECAR Asia project of University of Tokyo and United Nations University Institute for the Advanced Study of Sustainability with focus on developing strategies to enhance resilience to climate and ecosystem changes utilizing traditional bio-production systems in rural Asia. We would like to thank all the stakeholders and experts from various agencies in Japan and Sri Lanka for their comments and assistance.
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