日照市海岸带古河道分布特征研究

Study on the Distribution Characteristics of Paleo-channels in Rizhao Coastal Zone

根据收集到的日照市海岸带浅地层剖面测量调查资料,把多条浅地层剖面中出露的古河道断面推测性地连接起来,重建了以往的古河道体系,综合分析了日照市海岸带古河道的分布特征。日照近海区域存在一个主干河道呈SW-NE走向的梳状河道网,古河道形成于距今约4.4万a的末次冰期。古河道的形成是河流的侵蚀、搬运、沉积及后期的海平面上升、潮汐改造等多种因素共同作用的结果。在末次冰期,研究区内气候湿润,河流流速较大,河流搬运泥沙的能力较强,长期侵蚀作用形成下切古河道,在古河道中容易形成淤积较多河流携带的砂体。古河道断面形态主要呈U形、V形、W形、箱形和倒梯形。主干河道北西侧,分支河道较密,南东侧分支河道较稀疏。主河道长约40km,横截面由南西向北东逐渐变宽,最宽处达4km。分支河道多数以NW向为主,少数为NE向,长度介于8~20km之间,宽度约为1~3km。古河道主要位于16~24m水深的闭合深度以外区域,对其中的砂体经过粒度筛选可作为将来进行人工抛沙的砂源。

According to collected survey data of the coastal zone in Rizhao city,the ancient channel sections exposed in several shallow formation sections are conjectured,the old channel system is reconstructed,and the distribution characteristics of the ancient channel in Rizhao coastal zone have been analyzed comprehensively.In Rizhao offshore area,there is a comb like channel network with the SW-NE trend main channel.The ancient channel was formed in the last glacial period about 44000 years ago.The formation of ancient river channel is the result of many factors,such as river erosion,transportation,sedimentation,sea level rise in the later period,tidal transformation and so on.In the last glacial period,the climate in the study area is humid,the flow velocity of the river is large,and the ability of the river to transport sediment is strong.Under the long-term erosion,the ancient river channel is cut,and the sand body carried by the river with more deposition is easy to form in the ancient river channel.The cross section of ancient river channel is mainly U-shaped,V-shaped,W-shaped,box shaped and inverted trapezoid.In the north west side of the main river,the branch river is dense,and in the south east side,the branch river is sparse.The main river course is about 40 km long,and its cross section is gradually widened from southwest to northeast,with the widest section reaching 4 km.Most of the branch rivers are in the NW direction,a few are in the NE direction,the length is between 8~20 km,and the width is about 1~3 km.The ancient channel is mainly located outside the closed depth of 16~24 m depth,and the sand body can be used as the sand source for artificial sand throwing in the future.