Analysis of Isochronal Areas Over a Watershed Using Diffusive Wave Model Based on Rainfall Intensity Variation (Study Area: Kamanaj Olia Watershed-Tabriz)

The aim of this research is the application of two dimensional Saint-Venant equations for determenation of isochronal areas over the Kamanaj Olia watershed, a sub-watershed of Ajichay, located in East Azarbaijan Province, Iran. For this purpose watershed area was divided into 250×250 meters cells using GIS, then digital elevation model was prepared. Kostiokov infiltration model, as the best fitted model to measured infiltration data was selected for expressing infiltration component in Saint-Venant equations. Saint-Venant equations were solved using explicit method of finite difference numerical technique. Flow trajectory was calculated cell to cell to reach the outlet. Considering the momentary infiltration, the cell to cell flow rate was simulated using diffusive model for the purpose of spatial and temporal analysis.The equilibrium time for each cell was calculated to achieve the drivation isochronal maps for any rainfall event. Based on these maps the relation of concentration time with rainfall intensity as well as that of drainage area with rainfall intensity were developed.The eqiuilibrium time increased as the cell size changed from 250×250 to 300×300 and 350×350 meters, because of topographic and hydraulic parameters variation.