Incorporating seepage losses into a 1D unsteady model of floods in an ephemeral stream

Abstract

Zangemar River is an ephemeral river located in the northwestern part of Iran. Maku and Poldasht are hydrometric stations located upstream and downstream of Zangemar River, respectively. The measured flood hydrograph indicates that the output hydrograph volume from Poldasht station is significantly less than the input hydrograph for Maku station, though there are no lateral outflow branches and the amount of evaporation and direct removal from the river reach during flood events is negligible. These transmission losses can be caused by infiltration into the streambed and floodplain. Due to transmission losses and lack of initial flow, flood routing in these rivers is impossible to achieve through conventional methods and it is essential to develop new flood routing methods. Therefore, in this study a computer model for natural river cross-sections has been developed in which partial differential equations of non-uniform unsteady flow (Saint-Venant equations) are solved by finite difference methods. These equations have been developed by adding Muskat’s equation in such a way that seepage losses can be calculated simultaneously. The results showed that with consideration of seepage losses the developed model can predict the output hydrograph with good accuracy, compared to the field data. The results of flood routing for 13 input hydrographs showed that the seepage loss volume in the river reach is about 74% of the input hydrograph volume, on average. The model predicts seepage losses with a mean error of about 9.93% and the maximum error is less than 20%.

Keywords: flood routing, seepage losses, unsteady flow, Zangemar River