An overview of hydro-sedimentological characteristics of intermittent rivers in Kabul region of Kabul river basin

摘要

Intermittent rivers are defined as rivers with a high seasonality in water, sediment transport and habitat. In this study, an attempt is made to outline the major hydro-sedimentological characteristics of intermittent rivers systems using the examples from the Maidan and Shakar-Dara rivers in Kabul region of the Kabul river basin. As dominant hydrological characteristics of intermittent rivers, the interaction between surface water and groundwater is studied by correlating the precipitation, evapotranspiration, river discharges and groundwater level fluctuations in wells located in the vicinity of the rivers. Suspended sediment transport and river bed sediments are in a further step studied to understand the sedimentological behaviour of these river systems. The characteristics of the catchment area such as geology, land cover, land use and dry periods are studied to show their influence on the suspended sediment transport. Field observations and satellite images are used to investigate the morphology of the selected rivers. Results show that precipitation, in particular during the winter and early spring months exceed the evapotranspiration and are providing the main water source for irrigation and groundwater recharge. The analysis reveals that the seepage loss through the river bed contributes significantly more to the groundwater recharge than precipitation. An increase in suspended sediment concentrations in Maidan river are observed by comparing historic (1965-1968) and recent (2012-2015) data. In addition, higher suspended sediment concentrations are observed in Maidan river compared to Shakar-Dara river. The higher concentrations can be linked to the lower percentage of vegetated area in its catchment compared to the Shakar-Dara catchment as well as to its finer sediment grain sizes of its bed and banks. Morphological investigations indicate single and multi-thread (braided) channels are the most common planform types for Shakar-Dara river, however, at Maidan river with gentle slopes, a meandering tendency with various sinuosities can be observed.