Optimize the Irrigation Water for Agriculture in the Proposed Kalugal Oya Reservoir in Ampara District

This study attempted to propose a methodology to optimize irrigation water with optimal cropping patterns and annual net profits to the proposed Kalugal Oya scheme, situated in Ampara District, Sri Lanka. The optimization approach was based on linear programming. Three models were formulated: 1) Maximize net profit, 2) Maximize irrigable area and 3) Maximize net profit in Maha and maximize irrigable area in Yala. The above models were analysed with three scenarios: Scenario I Multi crop cultivation, Scenario II OFC and Vegetable cultivation and Scenario III Paddy cultivation in Maha and OFC & Vegetables in Yala. Further, four major constraints were identified in the above models. The first constraint relates to the availability of land (L) for agriculture use. The second constraint defines the total amount of available water (W). Third major constraint is related to the internal crop consumption (C_io) of a crop for food security requirement. Maximum level of crop production (S_i ) of a crop for local marketing capacity was considered as the fourth constraint. Considering agricultural year 2012, the total annual net profit gained from Scenario II of Model 1 is estimated to be 60 Million Rupees, which is almost two and half times greater than the profit obtained when traditional cropping patterns are used in these areas (26 Million Rupees). The highest annual net profit in Scenarios I and II of Model 1 achieved mainly from the cultivation of Kurakkan, Cowpea and Brinjal. However, to satisfy the need of internal crops consumption (C_io) of farmer families in these area, Paddy and Maize were recommended for cultivation though it is not profitable.