In this study, by taking the Dehloran flood diversion project as an example, the effects of this project were first examined in terms of flood control, artificial recharge of the groundwater table, permeability, vegetation restoration, and agricultural land area. Then, in order to evaluate economic indicators, the costs of constructing the flood diversion system were estimated, including the costs of studies and designs, excavation, stone and cement, planting, wages, and rents during the years of project implementation (1996 and 2003). Annual maintenance and repair costs were also calculated according to the volume of operations carried out each year. The results of the study showed that after the implementation of the flood diversion project, the flow pattern became a controlled network. Of the total volume of runoff in the plain (16.6 million cubic meters), 1.9 million cubic meters has been controlled and infiltrated, the permeability has decreased from 17.95 cm/h to 13.57 cm/h, the area of ​​cultivated land has increased from 7772 hectares to 12117 hectares, and the production of pasture fodder has increased from 50 kg/ha to 159 kg/ha. In economic terms, the added value from the injected flood was estimated at 171,990,000 rials, the added value of the produced fodder was estimated at 2,437,125,495,000 rials, and the added value of the agricultural sector was estimated at 1,182,456,690,000 rials. Based on the economic evaluation indicators (NPV, ROR and B/C) which were estimated to be 2517496964.76 thousand rials, 0.38 and 2.88 respectively, the flood spreading project is economically justified.