Tidal Bore Dynamics Around the Similar Right-Angle Shoreline in the Qiantang Estuary,China

Tidal bores are a unique hydrodynamic phenomenon during flood tide in the Qiantang Estuary.The tidal bore propagation around the similar right-angle shoreline is rarely documented in tidal estuaries.To investigate tidal bores around this shoreline,a hydrodynamic model combined with a theoretical method is employed to reveal the characteristics of the bore propagation.The theoretical solution of the tidal bore intensity is deduced to illustrate the relationship of the incident tidal bores and the back-flow bores during the propagation.The hydrodynamic model based on shallow water equation is employed to perform the simulation of tidal bores in the estuary.Model results with respect to the bore height and the propagation speed of tidal bores have a favourable agreement with field data.The tidal bore dynamics in the neighborhood of the similar right-angle shoreline are elucidated.The characteristics of tidal bores in terms of water surface,velocity,bore steepness and the intensity are illustrated and the back-flow bore is analyzed by numerical and theoretical methods around the similar right-angle shoreline.The height of the back-flow bore relative to the incident tidal bore ranges from 1.05 to 1.77.Model result reveals that the ambient water depth and the shape of the similar right-angle shoreline are contributed to the back-flow bore formation.

Effect of dike line adjustment on the tidal bore in the Qiantang Estuary,China

In this paper,the effect of the dike line adjustment on the Qiantang Tidal Bore（QTB）is studied by physcial experiments.A lab-scale physical model of the Qiantang Estuary is built and the tidal bore is generated.With this model,the formation and pro-pagation processes of the tidal bore are simulated with or without the dike line adjustment.It is shown that the adjusted dike line changes the direction of the reflected tidal bore.The height of the tidal bore increases in the upstream region where the dike line is contracted.In the tested bent and forking regimes,the bore height at the upstream station is increased by 0.10 m and 0.04 m,respectively.Furthermore,the crossing bore still exists near the Daquekou station and the location slightly moves by about 3 km to the downstream region.

Morphological evolution of a large sand bar in the Qiantang River Estuary of China since the 1960s

A large sand bar develops in the inner Qiantang River Estuary,China.It is a unique sedimentary system,elongating landwards by about 130 km.Based on long-term series of bathymetric data in each April,July,and November since the 1960s,this study investigated the morphological behavior of this bar under natural conditions and the influence of a large-scale river narrowing project(LRNP)implemented in the last decades.The results show that three timescales,namely the seasonal,interannual and decadal timescales,can be distinguished for the sand bar evolution.The first two are related to the seasonal and interannual variations of river discharge.During high discharge seasons or years,erosion took place at the upper reach and sedimentation at the lower reach.Consequently,the bar apex shifted seaward.The opposite development took place during low discharge seasons or years.The decadal timescale is related to LRNP.Due to the implementation of LRNP,the upper reach has experienced apparent erosion and currently a new equilibrium state has been reached;whereas the lower reach has been accumulated seriously and the accumulation still continues.Nonlinear relationships for how the bar apex location and elevation depend on the river discharge over various stages of LRNP have been established.Compared with the earlier stage of LRNP,the bar apex at present has shifted seaward by about 12 km and lowered by about 1 m.The sand bar movement has significant feedback on the hydrographic conditions along the estuary and has practical implications for coastal management.