Utilization of tail-escape weir for water conservation in distributary canals

Abstract

Egypt is facing an increasing problem of water deficit for irrigation and other uses. Most of the Egyptian distributary irrigation canals are operated using the rotational system where water is discharged continuously during irrigation period. However, farmers rarely irrigate during night hours and a significant amount of water is lost to drains. A strategy to reduce these water losses may be adopted by suggesting better operational abstraction patterns from off-takes that are distributed along the canal and by changing the tail-escape weir heights. An unsteady-flow model is developed to study the effects of different canal parameters: weir height, canal length and slope and off-takes abstraction time on the amount of water losses. It is found that water losses are significantly affected by the weir height and the abstraction time at the off-takes. Longer and milder canals provide more storage thus reducing water losses. Adequacy indicator for water supply considerably improves for longer abstraction time. A non-prismatic and deteriorated canal is investigated and results shows that deterioration of the canal cross-sections creates an additional storage and reduces water losses. However, deterioration has negative side effects in reducing canal conveyance and lowering water levels. Keywords: Adequacy indicator, Irrigation canal storage, Management losses, Preissmann scheme, Tail-escape weir, Unsteady-flow