Estimation of re-circulated drainage water in irrigation case study: Irrigation improved area in Egypt

Water consumption by crops can drop below the potential values under conditions of limited irrigation water supply. The deficit in irrigation supply can be reduced by official reuse of drainage water when mixed with irrigation water at specific known locations. If the amount of this reused water does not meet the deficit, farmers tend to use low quality water from randomly selected points at the nearby drains, unofficially. The amount of drainage water recirculated is unknown and sometimes represents a significant component of the global water balance of the area. A procedure to approximate the amount of recirculated drainage water has been proposed, so that the water balance can be adjusted accordingly. This enables the calculation of the overall irrigation efficiency, which was found to increase significantly with increased levels of water deficit and associated amounts of recirculated drainage water. The proposed method was sought by study of the influence of an Irrigation Improvement Project (IIP), recently undertaken in Egypt, on the water balance in the Mahmoudia area. In order to assess the project effects on future demands, quantity and quality of drainage water, and other related items, the water balance components were predicted for the improved area using the proposed procedure. Some of the IIP major components, such as the downstream automatic control gates and continuous irrigation flow, were also discussed and evaluated for the current Egyptian conditions.