Research On Physical Simulation Technology And Channel Improvement At Tidal River Mouth

It is well known that bringing a mouth-bar at a river mouth under control is very difficult. In this paper, firstly, the present research situation and current developing level of physical simulation on this subject is introduced; Secondly, the problem, harnessing the waterway across the mouth-bar at Guang-Li-He River Mouth, is put forward and solved.While choosing harnessing method, many factors, such as geographical position and characteristics of hydrology and climate as well as features of geography and sands, are taken into account. Waterway engineering and dredging method are used simultaneously. In other words, first decide one reasonable waterway at the river mouth, then dredge mud and at same time construct double water-diversion dikes composed of hydraulic slabs along the waterway at the river mouth so as to decrease cross-section area of flow, and accordingly increase flow velocity and ensure the flow inside the waterway to contain considerable sands and take them from the waterway to the sea outside.After deciding the harnessing method, according to horizontal scale 1:400 and vertical scale 1:50, models of Guang-Li-He River and sea area at the river mouth are done in physical test basin. Then water-level time series of rising tide and ebb tide at the riverway and river mouth are simulated properly by adjusting water-level time series near the tide tank, length and width of the winding waterway as well as roughness of riverway and river-mouth beach in model.With sands in prototype, the jump-start velocity, 0.54m/s, is given by 2-dimension test.To decide direction of the double dikes, the following factors are considered: direction of tide flow and strong ocean current, water depth as well as highest-wave direction and normal-wave direction. By contrasting flow velocity, flow direction, volume of dredged mud, length of dikes, difficulty index of construction and so on, one better design is selected by testing on four designs.The following steps are done to optimize the selected design above:(1) Move upper inlet of the double dikes nearer to lower reaches of the river; (2) Let thedikes turning a corner more smoothly; (3) Adjust all or part of the dikes' crest levels so as to change the flow state in the waterway; (4) Change direction of the outlet to northern-east for decreasing angle between strong-wind direction and waterway near outlet as little as possible; (5) Decrease width of outlet to increase the ebb-tide velocity at the outlet; (6) At the outlet, stagger the two ends of the dikes in horizontal surface preventing crosscurrent as tide rises.Through optimization above, the decided design for harnessing and the objectives following are achieved: (1) water level in the waterway changes steadily as tide outside rises or ebbs; (2) Flow velocity of ebb tide keeps constant or increased along the waterway; (3) Velocity and state of flow is proper and reasonable.