海底冲淤变化

CHAPTER 5 MARINE SEDIMENTATION Section 9 Change of Bottom Siltation

海底冲淤是海洋水文、地质等多种因素综合作用的结果。研究本区海底冲淤变化时,主要根据不同年代海图资料的对比与分析,并结合对海洋水文、沉积状况及沉积物年代测定、泥沙测定、调访等资料进行综合分析,以了解冲淤的基本趋势及主要形成因素。

From the correlation and analyses of historical charts and the synthetic analyses of the marine sedimentation,it ts understood Preliminarily the basic tendency and major formation factors of siltation change in Xiamen Harbour.In the West Port of Xiamen Harbour,the depth is steady in Xiamen-Gulang Island Waterway and the west of Songyu-Gulang Island Waterway over years;the tendency of bottom siltation increases in the east to Songyu-Gulang Island Waterway,the south of Houyu Islet and that arround Manwei Reef and Baozhu Islets,The sedimentation rate is 7.2cm/a according to 210Pb determination of cores from Station 34 in Baozhu Islet.Erosion deminates the area in Dongdu-Xiangyu Islet.There are two deposit zones in the outer harbour of Xiamen Harbour.Yuzhiwei-Dapan shallow bank is still an area of erosion.In Jiulong Estuary,sedimentation occurs to the west of Haimen Islet and the underwater delta.The topography of deep channel around Jiyu Islet does not change evidently though sedimentation is evident along the coasts.In Xunjiang region,the deposition tendency is increased in bay head.The area around Eyu Islet in the bay used to be and formed a good habitat for Branchiostoma belcheri and is now under siltation.From the analyses of sedimentation factors,it is believed that several causeways and reclaimation Projects along Xiamen Harbour since 1954 have led to reducing the sea area of the Harbour,weakening tide influx and hydrodynamic,and speeding uP deposition.At the same time the siltation has been increasing,in which the silt transported into the west of Xiamen Harbour comes mainly from land soil dumping while soil erosion along the coasts and the river borne sands are also important silt sources.