ABSTRACT
The amount of water and sediment that enters into an irrigation canal will vary during the growing season and, moreover, throughout the entire life of an irrigation system. Variations in crop water requirement, water supply, size of the irrigation area, planned cropping pattern and sediment concentration frequently occur during the lifetime of irrigation systems. The design of canals and flow control structures incorporates a certain degree of flexibility in the delivery of different irrigation flows at fixed or variable supply levels. This design approach also assumes that the conveyance of the incoming sediment is, for the given design conditions, in a state of equilibrium. Once the flow conditions diverge from the design values, the flow velocity and thus the capacity to transport the sediment load will vary in time and space along the irrigation network. Then, the initial assumptions related to the conveyance of the sediment load in equilibrium conditions are no longer valid for these changed flow conditions. Due to these changes, the sediment transport in the irrigation canal will essentially be under non-equilibrium conditions. Therefore, the transport will strongly depend on the variation of the initial flow and the changes in the incoming sediment load during the irrigation season and the lifetime of the canal. For that reason sediment transport should be viewed in a more general context, which should take into account the time and place of the varying operation requirements of the irrigation system.
