Abstract:
Deduru Oya region in Sri Lanka experiences highly variable flow patterns which pose a
challenge to water resource availability and distribution. The rainfall in the basin has a significant
temporal variation and thus the flow in the Deduru Oya carry flash floods during rainy season and
very low flow during dry season. There is need to store flood water carried by Deduru Oya for use
during lean season especially for irrigation. The multi-purpose proposed Deduru Oya reservoir
constructed across the Deduru Oya will have 75 MCM and the proposed irrigable area under Left
Bank (LB) canal is about 3000 Ha. This study aims to assess the cropping intensity of LB canal
area considering current and future water supply, demand status and water allocation with focus on
irrigation water requirements.
This study develops a model for water management in Deduru Oya LB canal
development area to study the possible water allocations of Deduru Oya LB canal irrigation
system. Hydrological Engineering Center-Hydrological Modeling System (HEC-HMS) is used for
hydrological simulations and CROPWAT model is used to estimate crop water requirements.
Water Evaluation and Planning (WEAP) model is used for water balance simulations in Deduru
Oya LB canal development area. Lump model results reveal that the cropping intensity in the
proposed irrigable area at LB canal will increase from 30% at present to 100% with the proposed
Deduru Oya reservoir.
