Water and sediment evolution characteristics of pool-riffle sequences in gravel-bed rivers of the East River

The East River is one of the confluence rivers in the Pearl River Delta, which belongs to less sediment river. Pool-riffle sequences are densely distributed in the middle and upper reaches of the channel, but the evolution characteristics of that under the condition of no sediment supply are not clear. Therefore, it is of certain scientific significance to improve the understanding of evolution rule. This study selected the sequences of the East River to measure the bed surface and bedload, and obtained the feedback between flow and bed morphology without sediment supply under different flow and slope in the laboratory. Experimental results show that the alternation of pools and riffles results in the discontinuous variation of average-velocity longitudinally, and the peak value of turbulent kinetic energy is easy to occur in the middle riffle under the shape of flood discharge. In the absence of sediment supply, the formation-destruction processes of periodic armoring layer occur alternately, in which static sorting is the dominant factor and leads to discontinuous gradation longitudinally. The increase of flow discharge and slope effectively promoted the sequence development, but at the same time shortened the length of pools and riffles. With or without upstream sediment supply, the variation of bedload transport in the sequence is enlarged, i.e., the bedload transport rate in the sequence increases with sediment supply; on the contrary, the bedload transport rate decreases without sediment supply.