Research On Restoration Of Muddy Sand Beach

Beach is an important part of the coastal zone.With the emphasis on coastal management,countries all over the world have carried out research on the beaches actively.At present,scholars have made some achievements in beach erosion prevention and beach nourishment,but there are few studies on beach muddy problems.Therefore,this paper will take Xinhe beach as an example to analyze the causes of the muddy beach and propose some useful methods to improve it.This paper analyzes the observed tide,suspended and bed sediment data in Xinhe Beach and its adjacent waters.In addition,a triple nested model is established by Delft3D to simulate the tidal,wave field and sediment transport,so that the cause of muddy beach can be analyzed.It showed that the lack of coarse sediment,flood current stronger than ebb current and the weaker wave are the primary causes contribute to the muddy formation.Therefore,a combined method of dredging outside the beach and sand supplement on the beach surface is proposed,in order to weaken the sediment transport by flood current,enhance the wave in front of the beach and increase coarse sediment.The variation of the wave height in front of the beach and the deposition of suspended sediment on the beach surface in different dredging plans are simulated.The results demonstrate that the dredging outside of the beach can effectively increase the wave height and reduce the deposition on the beach surface.With the decrease of dredging elevation,the wave height in front of the beach gradually increased and the volume of suspended sand deposited on the beach surface gradually decreased.For Xinhe beach,-7 m is the best dredging elevation.In this case,the annual volume of suspended sediment deposited on the beach surface is decreased by 56.6%and the wave height increased by 10%.For sand supplement,a morphological model of Xinhe beach is established by XBeach.It is used to study the response of the evolution of sand supplement profile to sediment particle size,porosity,design beach shoulder width,beach shoulder elevation and beach slope.The results show that the size of sediment particles and porosity have little influence on the erosion and deposition of the profile,but the influence is greater when the incident wave height is higher than 1.2 m.The width of beach shoulder has small influence on erosion and deposition of beach profile,while the elevation of beach shoulder has greater influence on it.Under the condition of incident wave height ?1.6 m,the volume of erosion is the smallest when the beach elevation is 3.0 m.The beach slope has a greatest impact on erosion and deposition of sediment supplement profile.When the slope of the beach is reduced from 1/10 to 1/30,the erosion volume is reduced by about 4/5 and 1/2 under the normal and strong waves respectively.Finally,considering the profile stability,the volume of sand supplement and restoration effects,the design parameters of sand supplement are as follows:the sediment particle size is 0.5 mm,the porosity is 0.3,the beach shoulder width is 150 m,the beach shoulder elevation is 3.0 m and the slope of the beach is 1/30.