Field Investigation And Evaluation Technology For Stability Of Coastal Beach

The coastline of Shandong Province is more than 3,000 km long,and about 80% of sandy beaches are being eroded.The main purpose of this study is to develop a methodology to assess beach long-term stability based on the field data collected from Yantai bathing beach.The Yantai bathing beach(37°28'7.53 "N;121°28'11.18" E)is composed of two sectors.One section at the northern side is a 2.5 km-long nourished beach,while the other section at the southern side is a 3.7 km-long natural beach.There are 20 permanent beach profiles surveyed in this study,and the distance between two beach transects is about 300~400m.The 20 beach profiles were surveyed every month.Periodic data collection,with fixed-profile,and fixed-point observations,were usually completed two hours before and after low tide.The coast of Yantai bathing beach has regular semi-diurnal tide,with the mean tidal range of 1.64 m.The low tide level and the data collection time of the next day were determined by the tide table.The maximum water depth of the underwater beach section collected at low tide was about 1.5 meters.In this study,the collected field data include: a)the beach profiles were surveyed with RTK-GPS to assess beach erosion hazard;b)The toe elevation of the dune and erect revetment walls were measured to investigate the effects of wave run-up and coast structures on the beach stability;c)The debris line or maximum wave run-up level was measured to study the effect of storm surge on the shoreline under extreme weather conditions;d)Three sediment samples for each profile were collected in the swash zone,dry-beach,and dune toe to investigate exchange mechanisms of sediment above and under water.Based on the reference You coast beach stability assessment technology,and through the lasted more than a year of field observation data,the stability analysis was carried out on the beach stretching,observed from a variety of data show that bathing beach of Yantai University in our measurement cycle as a whole was in a state of dynamic stable equilibrium,there will be no large-scale state of erosion and deposition.Based on the existing data and analysis results,it is found that there is a stable dynamic balance of the beach volume.In terms of beach slope,the slope of natural shoreline is obviously higher than that of artificial concrete shoreline and artificial beach shoreline.For the underwater part of the slope,the slope of the natural shoreline and the artificial concrete shoreline and the artificial beach shoreline are generally around 0.01,with a few special cases at 0.03.The underwater slope is much smaller than the water slope.Through the analysis of sediment particle size screening,it is found that the sediment particle size in the upper tidal zone,the middle tidal zone and the subtidal zone is not very different,most of the artificial beach D50 is 0.25 mm,the natural beach sediment particle size D50 is 0.4mm,very few beach profile sediment particle size D50 as high as 0.6mm.In general,the sediment particle size of Yantai University bathing beach is generally between 0.2mm and 0.6mm,which is within the range of medium sand and fine sand.