Erosion Mechanisms And Equilibrium Shapes Of Sandy Coast Of Headland Bays In South China

Sandy coasts are suffering from erosion, which gradually is attracting people's attention to. The headland bays are a ubiquitous morphologic form in the south of China. Headland sandy bays in South China as studying object, based on field measured date, adopted various means, according to different scales of temporal and spatial, erosion mechanisms and equilibrium shapes of headland sandy bays in South China were studied in this paper.The main objectives of the analysis were to probe into the variety rule of sea dynamics and morphology, the interaction patterns of dynamics and morphology in various scales of temporal and spatial, and provide such patterns a physical interpretation, based on the understanding of morphordynamics processes, seek the stable beach states and the form of static equilibrium shoreline.Waves are primary dynamics of sandy coasts. To understand the distributing characteristics of wave factors in nearshore is precondition of studying beach erosions and equilibrium shoreline shapes. The wave fields of Jinghai Bay were numerically simulated and wave distribution characteristics were analyzed. The results showed that the broken wave heights tended to ascend from shadow zone to tangent zone in headland bay coasts.Foreshores are the firsthand interaction area of lands and seas. The morphodynamic processes in the foreshore, which are intermediate or small scales relating cross-shore sediment transport, straightly reflect erosion-deposition mechanism of beach. Based on the measured data of beach profiles and waves in houjiang Bay, selected seven factors of dynamics, adopted canonical correlation analysis, four patterns of foreshore governing processes was explained, and the governing factors of each pattern were discussed. On the other hand, foreshores are the most drastic area of beach. The analysis of high-frequency beach oscillation in the swash zone indicated that beach face oscillation had several different frequency periods. Mechanisms which tide level effect beach and important effect of energy flux in the variation were discussed.Based on Morphodynamics, through analysis of beach state of jinghai Bay, It was discussed that beach state diversity of headland sandy bay in South China in temporal and spatial.Storm is an important factor of effecting coast erosion. Taken shuidong Bay as an example, response of shuidong Bay to 8616 typhoon was analyzed. The result showed that the effect of storm in coast was obvious, because of difference of beach state and shape, degree of erosion was different to the beach in different location of bay: degree of erosion was greater reflective beach than dissipative beach and tangent zone than shadow zone.Effect of sea level rise in erosion of coast is other important factor. Applied singular spectrum analysis, trend of sea level change was analyzed and discussed. Taken houjiang Bay and shuidong Bay as examples, adopted two project of 2.0mm/a and 2.5mm/a, applied Everts integral method, response of coast to sea level rise was forecasted. The result showed that a litter rise of sea level could make shoreline retreat large. Effect of sea level rise in calculation of extreme level distributing is obvious too. Applied extreme high level date of 31years in haimen station, frequency curve of P-â…¢and Gumbel were calculated. Through comparing and analyzing, the result showed that sea level rise caused extreme high level become higher.Longshore sediment transport is relational with coastal erosion processes of large temporal scale. Under normal waves condition, cross-shore sediment transport only takes sediment inside-and-outside, and can't cause coast erode in a long period. Sandy coast erosion is caused by longshore sediment in a long period. Mechanisms of longshore sediment transport and effect of longshore sediment transport in coast erosion were analyzed. Taken groynes being built as background, based on mechanism of longshore sediment transport, one-line model of headland bay was built. Change of shoreline was forecasted applying the model, and the effect of structure near shore to shoreline changing was discussed. The shoreline evolvement model as one-line model will bring great deviation, when simulating shoreline evolvement of larger temporal and spatial scale. However, equilibrium shapes rule of bay offers availability means for shoreline stability assessment of large temporal and spatial scale.Shoreline shapes model of nowadays all applied specifically function, such as logarithmic spiral, parabolic, hyperbolic and so on, to simulate shoreline. Problems of bay evolvement are complex and nonlinear, consequently, simple function can't describe the shape of equilibrium bay. Considered the back propagation artificial neural networks have the capability to deal with complex nonlinear problem, taken headland bay in the south of china as sample, a back propagation artificial neural networks model concerning equilibrium shapes of headland bay was built. In addition, definiens of front orientation and downcoast tip for shape model of nowadays was not reasonable. Through analyzing forming mechanism of static equilibrium shape, front orientation and downcoast were defined reasonably and the calculating means were provided.At last, applied the model to estimate the stability of 31 headland bays in South China, and discussed the application of coast-defend engineering...