Given that conjunctive use operation policies play a vital role in the sustainability of water resources and their optimal allocation, applying realistic conditions of water resource system in management models lead operating rules to be close to natural conditions. In this study, the combined fuzzy logic and direct search optimization technique has been used to account for the uncertainty associated with parameters affecting groundwater table level fluctuations. The mentioned effective parameters include specific yields and inflow recharge and outflow discharge from the aquifer which are often observed trivially or transitorily in management models. Using the hydrogeological area information and piezometric data, the fluctuation range of each parameter is specified to determine the membership function. Applying fuzzy cuts (numbers between zero and one) on each effective parameter and corresponding interval production, random search optimization model is implemented to find the minimum and maximum value of the groundwater table level fluctuations. The fuzzy number of the output parameter can be determined through replicating the above steps. To compare the results of applying uncertainty in providing optimal allocation values, a conjunctive use model was formulated with the aim of minimizing the shortage rate in supplying water demands given the water resources constraints. In this model, the area under study is divided into zones and given the priorities for each zone and considering the importance of the consumption and source types, optimal allocations are determined. The results of the proposed model show that if real conditions are considered in conjunctive use model, the reliability of system will be capable in handling the water supply demands. The results of the proposed model also indicate that it present reliable allocations compared to the static conventional models and that it performs more desirably and practically in allocating supplies to water demand
