| The Jiaojiang River empties into the Taizhou Bay eastwardly,which is the third largest river in Zhejiang.Jiaojiang Estuary is a strong tidal estuary of mountain nature,where is a strong sea-land interaction zone and a coastal sedimentary geomorphology,consists of cohesive fine sediment such as the silt,argillaceous silt and so on.On both sides of the Jiaojiang river is the muddy tidal flat.Because the cohesive fine sediment can flocculate easily,which is liable to cause the tidal destruction,port silting,water quality deterioration,and even ecological environmental problems.At the same time,the tidal current velocity has a great effect on the sediment flocculation sedimentation.As a consequence,it is important to carry out the numerical simulation research of the sediment settling characteristics in the estuary environment.On the one hand,we can obtain the tidal current velocity threshold,which affects the sediment flocculation sedimentation velocity fluctuation change point.On the other hand,we can analyze the siltation features of estuarine sediment through the solved settling velocity,and the main natural factors influencing the sediment accumulation speed on both sides of jiaojiang,which can provide constructive suggestions on the practical projects such as the construction of port and waterway,building of breakwater,reclamation engineering and so on.Based on the geological data and information above,this dissertation will use the sedimentology for theory basis,prefer the Rouse formula fitting to computing method,select the observed hydrological and sediment data of Jiaojiang Estuary in 2012 and 2013 as the basic data,and apply the Mapinfo,Matlab,CorelDRAW software and Excel comprehensively to analyze data and make maps.This dissertation has mainly studied the variation of Jiaojiang Estuarine sediment flocculation sedimentation velocity,obtained the tidal current velocity threshold of affecting the sediment flocculation sedimentation velocity,and analyzed various factors by the distribution features of settlement velocity,which affect the Jiaojiang estuary sediment deposition.Following conclusions can be made by the research of this dissertation:1.The Jiaojiang estuary tide is controlled by the estuarine horn geomorphology through the analysis of Jiaojiang landform and geological characteristics,estuarine hydrodynamic characteristics.As the influence of upstream and downstream river regime,the mainstream of flood current has always favored the north shore.But the mainstream of ebb current has always favored the south shore,which is forced by the bend mandatory force of upstream river.And the growth of jiaojiang river bed and basic pattern of river mouth of entering the sea is under the influence of geological structure deeply,the second is the holocene transgression,and the impact of human activities.2.Based on the characteristics of the mud sand diameter and composition,the sources of the suspended sediment in the Jiaojiang estuary are analyzed.The suspended sediment in Jiaojiang estuary is mainly composed of illite,montmorillonite,chlorite and kaolinite mineral composition,which mostly comes from the scouring of the upstream riverbed,erosion of the shore strata and the sediment of Yangtze River.According to the stratigraphic information,the sediment comes from the erosion of the quaternary strata of shoreside and Mesozoic strata of inland are concluded.3.It is the first time to apply the Rouse formula fitting method to the Jiaojiang estuary-Taizhou Bay,and the sedimentation velocity of suspended sediment at the S1,S2,S3 and S4 station in the Jiaojiang estuary is calculated.The range of the Jiaojiang estuarine suspended sediment settling velocity is 0.551-5.37mm/s,and the average suspended sediment settling velocity is 2.63mm/s amoung all the water.The average suspended sediment settling velocity of spring tide is 2.65mm/s,and the average suspended sediment settling velocity of neap tide is 2.60mm/s.The average suspended sediment settling velocity from large to small sorted by the spatial distribution is S1,S2,S3 and S4 station,that is to say the average suspended sediment settling velocity of the estuarine main channel area?S1,S2?is largest,then is the estuarine shoal area?S3?,and the last is offshore area?S4?.The calculated average suspended sediment settling velocity of Jiaojiang Estuary in this paper is between at the average suspended sediment settling velocity calculated by different researchers?0.01-10mm/s?,and has a more accurate range.Therefore,the calculated suspended sediment settling velocity of Jiaojiang estuary in this paper has a certain reference value for those who study the suspended sediment in Jiaojiang estuary.4.According to analyze the relationships among suspended sediment concentration,flow velocity and settling velocity,the reason why average suspended sediment settling velocity increases after 1-2h of going up/down to rest,afterwards it decreases is given.Finally the paper concludes that the tidal current velocity threshold of Jiaojiang estuary affecting the sediment flocculation sedimentation velocity fluctuation change point is 0.416m/s.At the moment of the go up/down to rest,the flow velocity close to zero,nevertheless there is still a large number of suspended sediment in the water.At the beginning 1-2h of going up/down to rest,the flow velocity increases.Before the flow velocity reaches 0.416m/s,the suspended sediment concentration is greater than the balance of sediment carrying capacity,causing sediment settling accelerating and then suspended sediment settling velocity increasing.As resistance and flow velocity increasing,settling velocity is weakened,thus settling velocity decreases.5.On the basis of the four stations' settling velocities,the distribution of the settling velocity field in the whole area of the Jiaojiang estuary-Taizhou Bay is drawn,and spatial distribution of settling velocity is confirmed.The average suspended sediment settling velocity from large to small sorted by the spatial distribution is estuarine main channel area?S1,S2?,estuarine shoal area?S3?,and offshore area?S4?.The settling velocity isoline of the entire area shows zonal distribution that near the mouth of the bay is larger,away from the mouth of the bay is smaller,and gradually decreases from shore to sea.Baisha is the boundaries,where is 18km away from the mouth of the bay.The settling velocity of bay water within the Baisha is large.However the settling velocity in the outside of Baisha fell sharply,and the closer to Taizhou Bay,the smaller the settling velocity.In consequence,the main sedimentation area is the shallow waters within the Baisha,especially the north and south sides of Jiaojiang estuary.And tidal current velocity is the main natural factor which influencs the sediment accumulation speed on both sides of jiaojiang. |
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