The Characteristics Of Tidal Linear Sands Off The Estuaries In Fujian, China

The coast of Fujian develops many estuaries along the winding coastline, and itsmarine environment is dominated by the Taiwan Strait. Estuary is closely related tothe human activities between the land and the sea. The Minjiang Estuary and theJiulongjiang Estuary are the small and medium-sized macrotidal estuaries, in Fujian.The distribution and evolution trend of the estuarine sand body affects humanactivities and economic development directly. Based on the recent survey data, ourresearch is helpful to strengthen the understanding and provides the theoreticalfoundation and reference basis of the geomorphic features of the small andmedium-sized macrotidal estuaries in our country. Based on the survey data bymulti-beam acoustic sounding, sub-bottom profile sediment, grain sizes analyses, aswell as the materials of the previous studies of the sea level changes，we studied thefeatures and the factors of the tidal sand ridges. Conclusions are as follows:(1) A certain scale of linear submarine sands which are referred to tidal sand ridgesoccurs off the Minjiang Estuary and the Jiulongjiang Estuary in Fujian. The sandridges off the Minjiang Estuary are oriented NE–SW, and some of them connected.The sand ridges off the Jiulongjiang Estuary are oriented ENE–WSW, and someappears to diverge on the end.(2) The main sand ridges are less influenced by the modern marine hydrodynamicenvironment affects. According to the analysis of the relation among the ridges scale,depth and relative distance to the estuary and the characteristic of grain size, thesediment source of the sand ridges is not the modern estuarine sediment. Their lowerstrata is composed of the residual deposit of the paleo-channel.(3) The ancient water depth calculated by the distance between the sand ridges isthe same with the Holocene sea level position and the water depth of the tidal ridgesformation on the shelf of the Yellow Sea and the East Sea of China. The sand ridgesof the Minjiang Estuary began to grow at the time from11to11.5ka B.P. which wasclose to the early evolution of the sand ridges in the China sea. The sand ridges of theJiulongjiang Estuary began to grow at the time from7to8ka B.P. which was close to the middle evolution of the sand ridges in the China sea.(4) It’s indicated that the tidal sands primarily originated from estuarine coarsesandy shoals on the paleo-channel system and were subsequently modified into thelinear forms during the period of Holocene transgression when sea-level rise wasdecelerated. The previous hydrodynamics of the estuarine environment is obviouslystronger than the recent one of the shelf plain environment. In the subsequent processof sea level change, water depth became deeper than the need of the sand ridgesgrowth. The sand ridges have been modified by the recent hydrodynamics evidencedby similar sand waves on both sides of flanks. The interaction by the recent tidalcurrent, wave and residual current leads to a relatively smooth surface on top and bothflanks of the sand ridges, and the main body of the sand ridges is basically steadynow.