Estimating of Unsteady Seepage losses in the Zangemar River Using Mathematical Model

Measured flood hydrograph of Zangmar Ephemeral River between Makoo and Poldasht hydrometry showed that the volume of exit hydrograph from Poldasht station is significantly less than input hydrograph in Makoo station. While there are not any lateral outflow from the river reach with 62 km length and the amount of evaporation and direct remove during flood occurring is very little. These transmission losses can be caused by water infiltration from the river’s bed and flood plains. Due to transmission losses and lack of initial flow flood routing in these rivers is impossible with conventional methods and it is necessary to develop methods of flood routing. Therefore in this study a computer model for natural river cross section has been developed in which partial differential equations of unsteady none uniform flow (Saint-Venant equations) is linearization by finite difference method. To calculate seepage losses Muskat’s equation integrated with Saint-Venant equations. The equations have been developed in such a way that seepage losses can be calculated simultaneously. The results showed that with considering seepage losses، the developed model can predict the output hydrograph in comparison with field data with good accuracy. The results of flood routing for 13 input hydrograph showed seepage losses in the river reach is an average of about 74% of the input hydrograph volume.