Experimental study on the formation and development law of delta deposition in shallow and narrow water basins

Abstract

This study conducted a generalized experiment of non-uniform sediment, in order to examine the formation and development laws of delta deposition in shallow and narrow water basins caused by constant water and sediment flow. A test of 425 h in duration is presented in this paper, and the results obtained from the experiment are as follows. First, the evolution process can be divided into two stages before the front of the sediment deposition reaches the outlet of the flume. In stage one, the front advancing of the deposition follows a certain cycle, and the front of the delta has an alternative development between the longitudinal advancing and lateral widening along the flume. The sediment first occurs longitudinally advancing along the water flow direction to make the front of the delta spread in the shape of a fan and lift through the constant deposition. Then, after the front deposition has been lifted, the topographical gradient along the way decelerates, which leads to the diversion water flowing toward the areas at both sides and constant lateral widening development. Next, after the lateral transport is blocked on the two side walls, the flow sediment turns back, inclines toward the central area, undergoing inclined spreading in a fan shape, and deposition lifting and development constantly occur during this process of spreading. With the increase of the test duration, the delta deposits in the area of both sides constantly undergo deposition and lifting, the water flow is centered and returned to the flume, then turns to the central area to further lift the deposition in the front of the delta through longitudinal advancing, and the above process is repeated. In stage two, the front of the delta deposition develops progressively without stagnation. Sediment constantly advances along the swinging flume, which causes the delta deposit to undergo deposition and lifting development in the swinging. Second, the paper analyzes the changes of the longitudinal advancing rate, lateral widening, and vertical deposition lifting rate shown in the two development stages of the delta. Finally, the paper analyzes the factors influencing the two development stages of the delta. The transportation of water flow and sediment is mainly controlled by three factors: the inertia of the inflow from the inlet, topography of the bed, and the side walls of the flume. In the evolution of the delta sediment deposition, the first influencing factor only acts in the initial stage, while the second and third factors are the dominating factor altering periodically in stage one, which results in the cycling of the front advancing. Meanwhile, in stage two, the evolution of the delta deposition is dominated by the other two factors.