Research On Sediment Transport And Control Factors Of Wendeng Offshore Area

Wendeng is located on the southeast of Shandong Peninsula and boasts ahigh-quality natural sandbeach and bathing beach on its offshore area. Characters ofsediment, hydrodynamics, sediment transportation and erosion of Wendeng’s offshorearea are analyzed in the paper by taking advantage of recent survey data, and theresearch result is of significance for cognition of sediment transportation in theoffshore area and maintenance of seabeach.Surface sediment types, grain size characteristics and law of mineral matterdistribution are analyzed in the paper according to173samples of surface sedimentand95samples of detrital minerals collected in July2013. Tidal current, wave fieldand erosion characteristics of the research area are simulated through the method ofnumerical simulation. The starting velocity of the surface sediment, the water depth ofwave breaking and coastal sediment transportation in the research are calculated andanalyzed through mathematical formulas of Dou Guoren, Sunamura, Sato, AmericanCoastal Engineering Center, etc. The change laws of water depth and landform areresearched with materials of water depth and landform of1980and the second phase of2013. Change features of the shore line of the research are compared and analyzedwith satellite imagery materials collected in2005and the second phase in2013. Basedon the former research, transportation characters of surface sediment of the offshorearea of Wendeng are analyzed and factors controlling the transportation of sediment arediscussed, and the research results prove:(1) Types of sentiment of Wendeng’s offshore area mainly conclude silt andclayed silt. Grain sizes of the sediment grow smaller gradually from the shore to thesea, and sorting becomes worse.35heavy minerals and14light minerals are analyzedand identified in the detrital minerals. In heavy minerals, content of flaky minerals likethe biotite increases gradually due to the significant impact of the hydrodynamic force.In the light minerals, distribution direction of the mineral content isoline of main light minerals like plagioclase is consistent with the wave mainly from south direction,which is the result of detrital mineral movement carried out by waves.(2) During the spring current season, the whole current direction is from east towest at the sharp point and from west to east in the fall urgent moment. Due to theimpact of New Port of Zhangjiabu, the wave action of the wave field in the researchcenter decreases, and a wave shadow zone is formed near the breakwater. The nearbysea area of the research area is mainly characterized by micro deposition, and theyearly siltation volume is less than2cm. The eroded area is mainly located at the headof the breakwater of New Port of Zhangjiabu, and the largest yearly erosion volume isabout16cm.(3) The overall migration trends of sediment of the sea area in the research areaare: the migration trend of coastwise (from Yangcunkou to Xiaolidao) surface sedimentis from southwest to northeast, from south to north on the west side of Zeku Peninsular,and from southeast to northwest on the south side of New Port of Zhangjiabu. On thewhole, the surface sediment gathers to Wuleidao Bay, and then the tidal flat terrain inthe bay is shaped and the current sedimentation situation is formed.(4) The surface sediment in the research area literally cannot be started by currentaction only. Currents play a leading role in transportation of silt after the surfacesediment on seabed is stirred by waves. The fact that “waves lift the sand, currentstransport the sediment” controls the transportation and distribution of sediment in theresearch area, and the distribution law of sediment that grain size is large in the middlepart and small in the east side and west side of the research area is formed.(5) Construction of the New Port of Zhangjiabu is the main human factor thatinfluences sediment transportation in the research area. After construction, New Portextends5km to the sea and that stops the wave mainly from east in the research area,and a wave shadow zone is formed in the east part of the research area. Variation of themaximum flow velocity in the dock and approach embankment reaches60cm/s, andnet sediment runoff on the west side of Zeku Peninsular is increased by52.7×104m3/a.The construction of the New Port directly changes the original shoreline and affects thehydrodynamic condition and the depositional environment, so that sediment transportation is influenced.