Effect of hydrodynamic dispersive and advective processes on watershed runoff (Case study: kameh watershed in Khorasan Razavi Province)

In the past, Geomorphologic Instantaneous Unit Hydrograph (GIUH) had been proposed as a tool to generation of flood hydrographs from storm rainfall data. Nowadays, Spatial Unit Hydrograph is used alternatively, with making use of Geographic Information Systems (GIS)., In this study, based on the concept of spatial unit hydrograph model for estimating the basin response is expressed and determined how the spatial size of the basin and hydrodynamic variables such as wave velocity and diffusion coefficient as advection and hydrodynamic processes affect the runoff basin. The parameter, W, was defined to quantify this important comparative. A series of simulations were performed for basins of different sizes and different spatial distributions of their hydrologic parameters. Result showed that if the hydrodynamic dispersion coefficient is null in all the cells, the flow is governed totally by the geomorphologic mechanisms and the value of W is equal to 1. In this case, a pure advection was done without changing the shape and hydrograph downstream spread and runoff hydrograph reflects the form of the time-area curve of the watershed and is characterized by high frequency oscillations. However, when hydrodynamic dispersion decrease, the hydrological response is influenced mainly by the hydrodynamic mechanisms and the value of the parameter W tends to zero. In this case, the hydrograph assumes a smoother form, presenting a well defined rising limb, peak value and falling limb.