福建九龙江口入海泥沙的扩散和河口湾的现代沉积

DIFFUSION AND MODERN SEDIMENTATION OF SEAWARD TRANSPORTING DISCHARGES IN THE ESTUARY OF JIULONGJIANG RIVER, FUJIAN PROVINCE

本文阐述了40年来九龙江入海泥沙量增加了两倍,入海泥沙在海门岛—鸡屿一带的浅滩区,其年平均淤积8—10cm,一次洪水流域搬来悬浮泥沙,使河口湾新淤积层厚2—3cm.并指出、进入河口湾的三条汉河各有独立的扇形粗粒冲积浅滩;悬移质的粉砂、粘土粒扩散至鼓浪屿以南海域;构成三角洲沉积主体的河口浅滩区的沉积速度由入海泥沙倍增而相应地加快进行.

The Jiulongjiang River is a middle river in the subtropical hilly area of southwest China. lts mean annual runoff volume is 120 x 108m3. Content of suspended sediment was 0.12g/L during 1950-1958 period, and up to 0.32g/l in 1980-1988. Correspondingly, total volume of sediments transporting into the sea increased from 1.12 x 106 ton to 3.38 x 106 ton (without bed mat-erial load). During 4 days from 22 to 26 of Sept. of 1988, one big flood took place, the suspended sediment of Jiulongjiang River was up to 1.27 x 106 ton into the estuary, exceeding the whole annual volume during each year of 1950's. All the bed material load and a part of suspended sediments are (deposi-ted in the seafloor northwest of Haimen Island or nearby, with a mean annual sedimentation rate of 100m/a. The other fine particles (<6) are trans' ported to and deposited in 1) deep water area southeast of Gulangyu Island in the Xiamen Bay, and 2) Dongdu Harbour, where the rate of sedimentation is generally 5-10cm/a. in average, and maximum can be up to 20cm/a. in some places. The main characteristics of modern sedimentation in the estuary of Jiulongjiang River are as follows: 1)In the branch channels, exist only medium-coarse sand deposits and no fine particles. In the mouth of each branch, there is a fan-shaped body composed of medium and fine sands. 2)In the shoal of the estuary (inner bay), are deposited fine-medium sands and clay, making up foreset of the estuary. 3)In the outer part of the shoal and in southeast area of the Gulangyu Is., the main sediment is clay and silty clay in the deep water. It is the bo-ttomset in the system of delta sedimentary environments. The increased sedimentation rate in the Jiulongjiang estuary is mainly caused by human activity, such as forest destroy, unreasonable civil engineering and severe soil erosion.