Effect of forest covers on water conservation and surface runoff reduction in Bazoft river

Function of water retention and avoidance of its loss, is one of the most important functions and services of the forest ecosystems which has a major role in provision of human welfare. In this study, in order to estimate the effect of forest cover on water retention and surface runoff reduction, the runoff depth has been calculated using Curve Number method. Firstly, study area has been homogenized in the basis of land use/land cover and hydrologic soil group's characteristics and the Curve Number of each homogeneous unit determined. Thus, the average weighted Curve Number for entire of the basin has been calculated. Lag time and time of concentration parameters of the basin were also calculated. Then, the input data were entered into the HEC-HMS model and the model was run using Curve Number (SCS) method for six observed rainfall-runoff events. Four hypothetical scenarios have been developed for the concept of water retention by forests and repeated the running of model for the developed scenarios.Results showed that in the case of scenario 1 which assumes that the entire of watershed area is covered by forests, the values of initial loss and lag time in the watershed has increased while Curve Number and flood peak discharge values decreased that indicates the role of forest cover on the prevention of water loss and its retention in the soil. Furthermore, the volume of infiltrated water in scenario 1 is about 2.7×106 m3.