The development mechanism of gravel bars in rivers

The development, stability, and growth direction of gravel mid-channel bars in rivers were studied by analyzing sediment distribution and vegetation development along the bars. Field studies and sediment sampling were conducted in the source region of the Yellow and Lancang rivers on the Qinghai Plateau. The results showed that the gravel bars in rivers always grow in the upstream direction, because gravel and sand are deposited at the upstream end of the bars. Gravel bedload stopped at the bar head. Sand and silt moved as suspended load during the flood season and were deposited at the bar tail due to vegetation resistance. Consequently, sediment size varied from gravel to sand and silt along the bars from the head to the tail on the bar surface. Dense vegetation coverage normally grew at the bar tail, while only pioneer species occurred at the bar head. The prevalent phenomena demonstrated the upstreamward growth of mid-channel bars.