Planning sediment distribution in surface irrigation systems

The object is to route water and sediment through an irrigation canal network so that sediment discharge equilibrium is achieved by diverting the sediment inflow with the farm supplies. A computer simulated canal network is used for the routing, and following problems are identified: (1) The sediment transport capacity in a branching canal network reduces in the downstream direction, mainly because smaller channels cannot transport their proportional share of the sediment load in the system. (2) The sediment transport capacity of farm watercourse channels is especially limited, and sediment discharge nonequilibrium in these channels can cause frequent interruption to farm water deliveries. (3) Sediment inflow on farm units necessitates recurrent land levelling. General principles for planning the sediment routing are derived. Results of laboratory and computer studies of sediment withdrawal in farm turnouts are also presented. The design of system components, so as to achieve sediment discharge equilibrium, is illustrated by a numerical example. Subject areas, where existing knowledge is deficient or unavailable, are also identified; and specific topics for field research are suggested.