Development and Application of the GFHM Distributed Hydrologic Model for Flood Hydrograph Modeling (Case Study: The Jafarabad Watershed, GolestanProvince)

Hydrological modeling is a major approach for prediction of hydrological responses of watersheds to different management scenarios. A GIS-based flood hydrograph modeling (GFHM) has been developed for simulation of event-based flood hydrographs using the PCRaster GIS and dynamic modeling language for The Jafarabad Watershed. The GFHM model is a spatio-temporally distributed hydrologic model. DEM، land use، and soil type maps as well as the precipitation hyetographs are the main input data required by this model. Regarding the temporal discretization of the model، a time interval of as small as seconds has been implemented. This minute time interval enables to the model، simulate the flood hydrograph of small watersheds with spatial discretization of a few meters. To this end، a conceptual model، including methods and relationships for simulation of different elements of the hydrologic processes، assumptions and limitations were defined. The GFHM uses the well-known method of curve number (NRCS) to calculate the rainfall excesses. The kinematic wave routing approach was used to route the generated excess rainfall of cells towards the outlet of the watershed. The one factor at a time (OAT) method has been used to carry out the sensitivity analysis. Based on the results of the sensitivity analysis، the CN and the Manning’s coefficient were chosen for the manual calibration of the model. Various assessment criteria were used to evaluate the model results. Results showed that the Nash-Sutcliffe efficiency criteria for the GFHM model were 0. 718 and 0. 777 for the calibration and validation datasets، respectively. Although the Nash-Sutcliffe criterion indicated the satisfactory of the model، resolving the time shift between the simulated and observed flood hydrographs through improvement in the model structure will enhance the performance of the model.