Study On Some Problems Of The River-mouth And Coastal Engineering Model Tests

A river-mouth or coastal area is the confluence of land and ocean. Necessary engineerings need to be carried out for for river-mouth harnessing, harbor, shoreline protection, environment protection and so on. In river-mouth harnessing engineering, it is important to study the verification methods of a river-mouth physcial tide model and to optimize the regulation plan of the navigation channel at a river-mouth bar by the model. For harbor engineering, as a technical support for its layout design, harbor water tranquility needs to be validated by a physical model or a numerical model.The detailed verification methods of river-mouth physcial tide model are studied based on Guangli river mouth which is a typical mild mix and marine deposition river mouth. The responses of the dominant model parameters to the tide levels at the river-mouth and the tide-current reach are included. Here the dominant model parameters consist of model length of the upper curved channels, methods of roughness, roughness areas and the tide-level curve at the control station ahead of the tide box. Taking the response laws as the important contents, a model verification method is given to improve its efficiency and precision.Taking Guangli river mouth as an example, system analyses of hydrometeorology, sediment and riverbed evolution of the one with mild mix and marine deposition are done. It is suggested that dredging and guard jetties should be applied simultaneously while regulating the navigational channel of a river-mouth bar with microscopic sand. By fixed bed tide model test, firstly four alternative channel directions are tested to study their effects on tide prism, the tide levels and the velocity distribution in the navigational channel of the river mouth bar. And among them, the best direction, which is consistent with the surveyed facts, is decided. Secondly, on the basis of the best direction, the effects on the velocity, flow direction and local flow pattern in the navigational channel exerted by its area of wetted cross section, the elevation of jetties, the swirling flow at the round segment of the navigational channel, the layout form of the jetty outlet are studied. The results of the local movable bed test also show that the velocity and the flow pattern along the channel of the final plan are reasonable which can basically maintain the channel water depth and satisfy the sailing conditions for designed ship. Finally, the studies show that contribution of each portion of the jetties for maintaining the channel water depth is greatly different. For a more economical investment, the jetty project should be divided into several portions and the construction schedule of each portion depends on its own contribution.When studying the harbor water tranquility with a physical model or a numerical model, a case is often confronted that the angle between the generation line and the isobath is so large that the differences of the wave climates along the generation line can not be ignored. For this case, the incident wave boundary is difficult to evaluate:(1) In a physical model, it is feasible to decide the incident wave boundary for one-entrance harbor by one verification point located at the entrance and'one-line generation method'; but for a multi-entrance harbor, this method is found that different position of the verification point will result in different harbor tranquility and the test error is so evident. (2) Some numerical models, such as the Boussinesq model of Mike21 which is widely used currently, cannot provide the natural wave distribution along the generation line.In order to solve this problem, firstly by several demonstrations, it is recommended that in the Boussinesq model of Mike21 the verification point should locate at the harbor entrance instead of locating on the wave generation line which is a model boundary, and the 'modulation method' widely used in a physical model to determine the inputs for the wave generator according to the output should be introduced into Mike21 to modify the incident wave boundary of Boussinesq model on the original topography. Secondly, due to the deficiencies of a physical model and the Boussinesq model of Mike21, a multi-line wave generation method is proposed for a multi-entrance harbor, with each line generating waves at the same time independently and each entrance having its own verification point. Thirdly, this method is applied to a case that the harbor is designed with two entrances and the angle between the generation line and the isobath is near 90°. And the results are reasonable.