The Evolution Process And Stability Analysis Of The Yanda Beach Profile

The total length of Shandong coastline is about 3300 km,59.4%of which the sandy coastline is eroded.Once the sandy coast is eroded,the beach face will be narrowed,the sediment will be coarsened,the slope will be steeper,and the space of the coastal zone will be reduced,which will have a great negative impact on the ecological resources of the coastal zone and human production and life.Yanda beach is bounded by the watchtower on the south side of the Yellow Sea Pearl trestle and the northwest side of Yantai Nature Museum,with a length of around 7 km.Yanda beach is a typical beach in Shandong Province.The research on its evolution process and stability can provide a potential reference value for the maintenance of Shandong coastal beach and the construction of coastal engineering around the beach.In this paper,the hydrodynamic forces of the sea area near Yanda beach are simulated and analyzed by FVCOM model and SWAN model,and the measured data are used to validate the accuracy of the model.With the estuary of the Guangdang River as the dividing line,there are 10 profiles on both sides.Taking the P19 profile as an example,the hydrodynamic numerical simulation results are used to explore the influence of hydrodynamic on the evolution of Yanda beach.Based on RTK measurement technology,20 profiles of Yanda beach are collected once a month.In the month when typhoon passes,two measurements are conducted before and after typhoon.The collected profile data are processed and analyzed,including the unit-width volume of the profile,the overwater slope and the underwater slope,so as to analyze the evolution process and stability of Yanda beach.The collected surface sand samples are dried and screened in the laboratory.According to the surface sand sample data obtained after screening,the change and distribution characteristics of surface sand particle size are analyzed,and the evolution process and stability of Yanda beach are further investigated.Based on studies,it is found that:(1)In the winter of 2019,the tidal residual current in the sea area around Yanda Beach was mainly offshore current with a large velocity,In the summer of 2019,the tidal residual current was mainly shoreward current with a small velocity.The wave height was mainly concentrated below 1.5m.The effective wave height reaches the maximum in autumn and the minimum in summer.(2)The variation range of unit-width volume of different types of profiles is mainly concentrated between-0.05m~3/m and 0.05m~3/m.The overwater slope of Yanda beach's concentration range is more significant than that of the underwater slope.The overwater slope variation of all types of sections is mainly between-0.01 and 0.01.The interpretation of the submarine slope is mainly between-0.005 and 0.005.(3)In terms of the surface sediment's transverse aspect,the particle sizes of the three sand samples in the bottom angle of the dune,the berm,and the wave-scour area of each sand sampling section have slight differences and do not change significantly with time.In the longitudinal direction of the surface sediment,the particle size of the P1 profile is fine sand;The P4 profile is the second part,which is the medium sand;There is no significant difference in other profiles.All of these are medium sand.(4)Under the influence of hydrodynamic factor,the amount of sand in the summer of 2019 at Yanda Beach is relatively large,and the particle size in the wave-scoured area is relatively fine.In the winter of 2019,the amount of sand is relatively small,and the particle size of sediment in the wave-scoured area is relatively coarse.(5)After Typhoon"Lekima",Yanda beach was eroded,and the beach erosion from P2 to P14 profile was relatively serious.Although the shape of natural dune profiles such as p17,P18,and P19 changed significantly,the amount of sand had little change.(6)The variation of unit-width volume,overwater slope,and underwater slope with time are tested for stationarity.It is found that the unit-width volume,overwater slope,and underwater slope of each section are always in a dynamic equilibrium state in the process of changing with time.Therefore,Yanda Beach's stability is good from the perspective of the variation of unit-width volume,overwater slope,and underwater slope.The median particle size of the sand samples at each sand extraction site was relatively stable over time,and there was no significant change,so it is clear that the stability of Yanda beach is good.