In order to increase the water delivery efficiency of an existing irrigation system, it is proposed that modern mathematical optimization techniques be applied to the management of irrigation water delivery. A deterministic mathematical model is developed to simulate the events that occur in delivering water, from a supply to the users, in an interconnecting, open channel irrigation system that contains reservoirs. The events considered are inflows, outflows, losses return flows, demands and storage. The simulation model is developed so that it can be linked to nonlinear programming and optimal results obtained. Two example models were constructed, using the linearized simulation model, to illustrate model construction and solution. The results of these solutions show the model adequately fulfills the purpose for which it is intended. The model solutions also demonstrate the effects of including future time periods in an analysis and the effects of modifying a structure in a system.