Stability And Sedimentary Behaviors Of Headland-Bay Beaches

The distribution characteristics of the sediment and the changing characteristics at different spatial and temporal scales on the headland-bay beach are the most direct reflections of beach sedimentary system and dynamic morphodynamic processes.The change of beach profile is a short term morphodynamic behavior related to cross-shore sediment transport,while the shoreline change related to longshore sediment transport is a long trem morphodynamic behavior.The headland-bay beach stability is analyzed comprehensively by the study of the morphodynamic behavior,Hainan Island is an important location with rich natural resources,The economic activity will be more frequent here with the strategies of Hainan International Tourism Island and the Western Development.The study on sedimentary behavior,morphodynamic behavior and headland-bay beach stability are supplement to the theory of headland-bay beach,also to Hainan's resource development and environmental protection.In this paper,the beach stability of research area is analysised based on remote sensing images over the recent 40 years and MEPBAY model developed from parabolic bay shape model.Meanwhile the sedimentary behavior of four typical headland-bay beaches along Wanning coast in east Hainan Island are analyzed based upon the data of beach sediment grain size and grain shape which is gathered during December 2014,August 2015,July and December 2016 and the Self-Organizing Neural Network Model(SOM).The result in detail is listed below:(1)The results suggest that the evolution of the beach profile is more complex in short term,and related to the headland-bay shape characteristics and the nearshore geology and geomorphology.(2)There is no significant change in the four headland-bay shoreline,generally in a relatively stable state except for the obvious changes in the eastern side of the Bao-ding Bay and the shoreline salient of Dong-ao Bay based on the analysis of the shoreline over the recent 40 years.(3)Parabolic bay shape model is applicated to the headland-bay beach stability in study area.However the existence of submerged reefs and shoals cannot be ignored in selecting suitable headland control point,and only by selecting suitable headland control point to be better predict the erosion or deposition state of beach.(4)There is no significant sediment exchange between adjacent beaches and each embayed beach is a relative independent geomorphological unit.The results show that the four headland-bay beaches are in or close to static equilibrium except the shoreline salient of Dong-ao Bay in an unstable state.(5)The distribution characteristics of the sediment component,grain size,grain shape and grain shape parameters in study area have significant spatial variation and relation to the shape characteristics of headland-bay and landform of nearshore.Beach sediment size and shape distribution displays a significant difference between sheltering and open section and their characteristics are significantly influenced by the shelter effect of headland-bay.(6)In the study area,the grain size and parameters distribution in vertical samples of WH14H and WH14Z have a significant laws.