Assessment of subsurface riverbed clogging by fine sediments in a semi-arid catchment of north-western Algeria

Abstract

In semi-arid regions, natural and anthropogenic disturbances increase the input of fine particles and their subsequent accumulation in streambeds sediment. The clogging of streambeds sediment is caused by the infiltration of fine particles at depth, reducing hydraulic conductivity (K) and hyporheic flow. Grain-size distribution and streambed vertical K were estimated using hyporheic sediment samples collected from ten stations in the Tafna River catchment during two hydrological periods of high and low water in order to investigate spatiotemporal variations and the variables influencing hydraulic conductivity. During the wet season, the upstream part of the catchment had significantly higher coarse sand content, with K measured to be three times greater than downstream. During low flow periods, there were significantly more fine particles (clay and silt) downstream, which were negatively correlated with K. Increases in clay and silt were the main cause of sediment clogging in the downstream part of catchment. However, within-group PCA showed that geomorphology had no significant influence on hyporheic sediment clogging. This study demonstrated that the process of streambed sediment clogging was influenced by the accumulation of fine particles and organic matter, which significantly contributed to the clogging of the downstream hyporheic zone, thus decreasing hydraulic conductivity despite prevailing geomorphology.

Keywords: geomorphology, grain-size, hydraulic conductivity, hyporheic zone, Tafna River