舟山岛马岙岸段海岸演变与水下岸坡冲淤动态
Coastal evolution and erosional accretion dynamics on the subaqueous shore slope along the coast section at Ma’ao coast of Zhoushan Island in China
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摘要: 利用不同年份的水深地形资料进行冲淤计算,结合实测水文泥沙、现场岸滩沉积地貌观察、新老海堤分布位置及以往浅地层探测和考古等资料综合分析发现,岸滩地貌形态从大约距今7 000 a前的一个古基岩港湾经受细颗粒泥沙长期不断地充填、淤积转化为近乎平直的岸段.在自然和人类活动的共同作用下,近370 a来海岸线以5.3 m/a的速度向海推移,潮滩以0.25 cm/a的速率沉积.近40余年来水下岸坡平均冲淤速率为-3.8~2.4 cm/a,横向冲淤调整有类似砂质海岸剖面塑造的特性,泥沙经受了在横向剖面"上部微淤、下部微冲"和纵向总体"东侧微冲、中西部微淤"的交替重复调整过程,目前朝着"上部微淤、下部微冲"的均衡剖面调整方向发展.Abstract: It is shown that the coastal configuration has been changed into the nearly straight coast from a rocky ancient bay, about 7 000 a B. P., w hich is filled with fine grain-size sediments for a long term, comprehensively analyzed with the data on comparing the bathyorography in differenty ears and calculating sediment erosion and accretion on the subaqueo us shore slope area, combining among the observed tidal current, suspended sediment, coastal sedimento logical geomorphology in the field and the distribution in the new and old sea dykes, the previous subbot tomprofiling and archaeological results, etc. The coastline is seaw ards advanced at the speed of 5.3 m/a, under the action both the nature and humanactivity, and the tidal flat is deposited at the speed rate of 0.25 cm/a in the recent 370 a. The average erosion and deposition rater anged from -3.8 to 2.4 cm/a on the subaqueous shore slope area over more than 40 a. The erosional depositional processes are similar nearly to the const ructive characteristics of coastal sandy profile. Sediments repeatedly under went the process in the alternate adjustment of "the slow accretion in the upper part and slighterosion in the lower part" on the on shore off shore profile and did on the whole "the sligh terosion in the eastern end as well as slightaccretion" both in the middle of and in the western end of the alongshore direction. This slope area is developed at present tow ards adjusting an equilibrium profile in the direction of "slow accretion in the upper part and slight erosion in the lower part".
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