Canal Capacities for Demand Under Surface Irrigation

Abstract

Providing water to users on demand usually requires an increase in canal capacity over the same volume of water delivered at a uniform rate. A simulation model was used to develop demand patterns for hypothetical surface irrigation conditions. These results were used to determine the canal capacity required to meet various levels of demand. A modification to these results was hypothesized to be appropriate for delivery schedules where delivery is arranged. These results are expressed in simple, nondimensional terms and compared to capacities for continuous flow and rotation systems and to capacities from Clement's demand formulas. It is shown that Clement's formulas which were developed for sprinkler irrigation are inappropriate for surface irrigation demand since they do not account for the wide variations in possible conditions. Results are particularly inappropriate for small relative service areas. Simple canal capacity equations were developed for demand and arranged surface irrigation distribution systems for a 90% level of service (i.e., water is available 90% of the time when demanded).