Effect of Riffle Sequences on Discharge and Sediment Transport in a Mountain Stream

Natural riffles are formed as a result of fluvial processes in the stream channel, water flow, and sediment movement. In recent years, artificial riffles have also been constructed in order to improve water flow and sediment transport as well as to initiate processes that lead to the restoration of natural riffle–pool sequences. In river engineering, the utilization of artificial riffles (rapid hydraulic structures) is still in its experimental stage. Artificial riffles are studied and described in the literature on a case study basis. However, studies on riffle sequences and their effects on stream channel evolution need to be improved. A system of artificial riffles was created in the mouth section of Krzczonówka Stream in 2013. The new riffles made the stream channel more morphologically diverse and also reduced its longitudinal slope. The check dam on the stream, located upstream of the newly formed riffles, was renovated and lowered in 2014. At this time, a flood occurred and released a large mass of sediment downstream of the check dam. Then, the sediment settled in the sections between the artificial riffles, thus covering some of them. The aim of the study was to examine the effect of the system of riffles on changes in sediment transport and water flow in the studied stream channel. Calculations indicate that the system of riffles established downstream of the check dam has limited the movement of sediment. Sediment transport is varied throughout the studied stream course and is mostly dependent on the sediment supply.