Coastal evolution and erosional accretion dynamics on the subaqueous shore slope along the coast section at Ma’ao coast of Zhoushan Island in China

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".