Determination of erodibility or sediment ability of river reaches using

The human activities and natural factors cause changes in sediment supply rate in the rivers. The rivers naturally react to this change to balance themselves to the new imposed conditions. This transformation is continued until the river section is reached to dynamic equilibrium. In this study, Erodibility or sediment ability of Gheshlagh River reaches are determined based on the critical velocity by means of different methods (Fortier table, Mavis method and Hjulstrom diagram). At first, cross sections of studied river are provided using the basin's topographic maps and ArcGIS 9.3 software and later Gheshlagh River is modeled and simulated in steady flow state, aiding HEC-RAS software. Results obtained from simulation and performed computations indicate the differences in results obtained from morphologic variations determination methods in Gheshlagh River so that according to two methods Mavis and Hjulstrom, all sections of Gheshlagh River are exposed to scour whilst in Fortier method, some reaches are sedimentary.