In recent years, using non-structural methods especially forecasting flood has increased the success of

flood control as well as structural methods. The main purpose of this research is to estimate the effect of

watershed management on flood forecast lead time in Golabdare-Darband basin using HEC-HMS model.

We defined five scenarios for different land uses, including conditions of 1955, 1988 and 2001, suitable

and unsuitable watershed management. The land use that was used in this paper is similar to the land use

of 2001. The HEC-HMS model is calibrated using recorded rainfall and flood hydrograph and it is verified.

Floods of different return periods are simulated. The forecast lead time is estimated for five scenarios

using the 25-year peak flood (for the scenario of 1988) as a threshold flood warning. The result shows

that the lead time increases by decreasing in return periods. The Comparison of forecast lead time between

five scenarios shows the forecast lead time is longest for 1988 land use. The forecast lead time of unsuitable

management was decreased to 35 percent of the forecast lead time of 1988 scenario. The shortest of

forecast lead time was for unsuitable management of the watershed.