Modeling the effect of vegetation-based management scenarios on hydrologic responses of the Ghazaghli watershed, Golestan province, Iran

Nowadays, evaluation of soil and water conservation projects are the most fundamental issues in order to increase the efficiency of natural resources planning and management. . Due to lack of necessary equipment and tools to measure and record changes induced by critical phenomena such as flooding and degradation, application of models to evaluate different management scenarios aiming to attain the goals is inevitable. Purpose of this study is assessment of the impacts of vegetation-based management scenarios on hydrologic responses of the Ghazaghli watershed using the SWAT model. To this end, four management actions including terracing, afforestation, orchard plantation and agroforestry were chosen. Different combination of these four actions leads to 16 (2n) different management scenarios. Rationale method was used to estimate runoff depth and SCS method was used to estimate volume of runoff. Furthermore, the Muskingum and FAO Penman-Monteith methods were used for flood routing and estimation of ETo, respectively. The simulation of all possible scenarios indicated that a scenario combining all management actions (scenario 16) is the most effective scenario in reducing runoff. Whereas this scenario leads to 13/15 percent reduction in the annual runoff volume.. Among the individual scenarios, the scenario 5 with Agroforestry action resulted in the largest decrease in the annual runoff which was 11.6 percent. The largest reduction in monthly runoff has occurred during June and July. This period of year coincide with the maximum growth of vegetation cover which induce the increase of evapotranspiration and consequently decrease runoff volume.