Sedimentary Dynamics Process And Topographic Evolution In The Modern Yellow River Mouth

Based on the historical data of Yellow River Delta and Laizhou Bay, a series ofsedimentary dynamics models have been carried outby MIKE3. After the modelsvalidation by using the observed data, the evolution of tidal current, shear front andwaves in Yellow River estuary since Yellow River’s diversion to Qinshuigou Channelin1976has been simulated. Combined simulation results and the observed datashowed the changes in Scour and Silting of Topography.The change patterns andcauses for tidal shear front in Yellow River through a whole flow route, under thecombined effects of strong wind and topography, and the potential dangers inengineering with the change of dynamics in Yellow River estuary have been studied.According to the analysis, the intensity of shear front is constantly stronger in low tidethan in rising tide., The interactions and patterns between evolutions of sedimentarydynamics and topography have been explained. The dynamics of winter’s sedimentdiffusion in Yellow River estuary,caused by the, has been disclosed based on thechanges of shear front, and the particular theory of dynamic parameter design formarine engineering environment in Yellow River estuary has been proposed and thecorresponding precaution system as well.The tidal shear front and tidal current field have showed a prominent evolutionalpattern in term of space, time and intensity during the20years from1976to1996when Yellow River has diverted to Qinshuigou Channel. The underlying cause for theevolutional pattern is the change of topography. The evolution of shear front reflectsthe evolution of tidal current field. Furthermore, the evolution of tidal current fieldand the topography in Yellow River estuary have coupled interaction with each other,i.e. the growth of estuary will promote the growth of tide, while the growth of tidewill limit the growth of estuary, which will stay stable in a certain amount of Runoffand Sediment Transport. The retrogression in the estuary will weaken the tide, so theerosion will be weakened as well as the rate of erosion.The strong wind has a predominant impact on tidal shear front in Yellow Riverestuary. A gale at six can change the shear front; the stronger the wind is, the greaterthe change will be. The wind-driven currents caused by the strong wind in off-shore shallow water lead to the change of shear front. If the wind is parallel to the frontalsurface, it will make the front stronger and if the wind is vertical to the frontal surface,it will weaken the intensity of shear front. Besides, the north wind will intensify theshear front in low tide but it will weaken the shear front in rising tide. However, thesouth wind is utterly contrary. It is well known that the topography is both thedetermining and necessary conditions for the winds to have an effect on shear front.In such circumstances, with the help of north wind in winter, the changes such asweakened shear front, disappearance of shear front in river mouthand in rising tide,will be benefit for the expansion of sand and silt in Yellow River estuary. What’s more,a large amount of resuspension of sediment will break through the resistance of theshear front under several circumstances and diffuse to the middle or mouth of LaizhouBay. The impact of wind to the change of shear front plays a key role in thesupplement of silt in winter.Due to the asymmetry in the process of tide in Yellow River estuary, the speedand time of tide-falling is greater than tide-rising, which makes the shear front in lowtide is greater than it in rising tide in terms of the length, duration and shear strength.The differences between these two shear fronts will be amplified with the influence ofnorth wind, even in some fewer cases the shear front in rising tide will almostdisappear. This pattern mentioned above existed commonly under the influence ofasymmetry in tide and monsoon.Wave recurrence period in Yellow River estuary has been significantly affectedby topography. If the average depth of water in old estuary of Qinshuigou rises1meter, the significant wave heights from northeast which will happen once in fiftyyears will grow by0.4meter. During1996to2012, the wave heights has increased by1.1meter, and the increasing rate is about0.07m/a. According to the changes of waveheights, the Yellow River estuary has been divided into three parts: safe new estuary,endangered new-old estuary, and dangerous old estuary. In the coming10years, theendangered and dangerous areas will suffer from sea-shallow and enhanced wavescaused by the shoreline retrogression.Based on the results of interaction between dynamics and topography, somesuggestions have been proposed on the alternative flow routes for Yellow Riverestuary and potential problems attributed to the rapid changes in the marineenvironment caused by offshore engineering. It highlights the urgency and necessityfor the promotion of the theory of dynamic parameter design for marine engineering environment and precaution system. Furthermore, advice such as several sets ofparameter design, regular investigation and remedy for precaution has been providedfor implement of this theory.Eventually, after3years of research, this article has many novel ideas as follows:1. Disclose of the evolution patterns and causes of tidal shear front in Yellow Riverestuary in a whole flow route in Yellow River, which explains the interaction andevolution process of topography and tidal current field.2. Discover the response pattern of tidal shear front in Yellow River estuary to thestrong wind, and a new dynamics of sand and silt diffusion in winter in Yellow Riverestuary has also been revealed, which consummate the research on the expansion inwinter in the estuary.3. Explicit the changes of shear front in low tide and rising tide under thecircumstance of common and extreme meteorological conditions, and the causeswhich make the shear front in low tide is constantly stronger than the shear front inrising tide.4. Study the response of wave recurrence period in Yellow River estuary totopography and the theory of dynamic parameter design for marine engineeringenvironment and a precaution system have been proposed.