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Poster Session
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Satellite observation of south coast of Bohai Bay
We take E118045' as a boundary to subdivide this segment into two parts. The western part was the main depositing area of the sludge from the Huanghe River from 1974 to 1976,' beach propagated seaward significantly. Steep frontal slope and loose deposits resulting from fast deposition have caused strong retreat-by - erosion after the water-way change of the Huanghe River May, 1976. Retreat-by-erosion effected the whole segment, and achieved the maximum rate during the period from 1978 to 1980. The theoretical zero depth contour of 1980 shrunk landwards of the zero depth-contour before the flood of 1975, and sub water slope of this segment became gentler and width increased. After 1980, retreat rate has tended to slow 1976, change of the mean high tidal line has kept pace with that of the zero depth contour and the retreat magnitude is not lower than erosion magnitude of the zero depth contour. and the retreat magnitude is not lower than erosion magnitude of the zero depth contour. From the vertical view, depth of down erosion is not very large from 1976 to 1985, the maximum depth of down erosion was no more than 4 m, showing that main result of retreat-by- erosion is lateral coast retreat. Satellite images can show the result directly (Images 1,2,3,4). Compared with the west part. sludge deposition stopped earlier along the east part. Which has ex-
perienced erosion for a longer time, and has a loser retreat rate. Retreat-by-erosion can be observed clearly in both vertical and lateral views. From 1976 to 1985, an obvious center of down erosion had developed in the underwater area, the erosion depth reached up to more than 6 m. This is the cause often washing at the platform bases in this area. The embankment built recent years for petroleum development has been eroded and collapsed locally. In addition , there is a non-tide area with small tidal difference and strong tide current. The coast adjacent to this non-tidal area has been more strongly eroded and become narrower.
Main conclusion
Based on the above analysis, we can conclude as follows:
- The south Bohai Bay coast can be divided into two segments : weak retreat-by-erosion segment and strong retreat-by-erosion segment . The topography of the former one changes slowly with a broad beach, a gentle slope, weak erosion and a stable erosion cliff. In contrast, the topography of the later one laterally changes strongly with a narrow beach and a steep slope, and without a stable erosion cliff..
- Erosion at the protruding part and deposition at the elepressing part are one of main manifestation of retreat-by-erosion. Erosion at the protruding river mouth makes the coast smoother and retreat rates along different part of the coast be similar.
- Another important expression of retreat-by-erosion is the change in beach topography ----that beach becomes gentler and wider, and tend to be not faver to erosion.
- On a profile view, erosion occurs at the upper part of the whole coastal slope, and deposition does at the lower part. The transition between erosion and deposition lies slightly above the coastal slope break. Toward land from the transition are located erosion areas.
- Coast retreat landwards and water deepening by erosion make petroleum development difficult. Only with the full knowledge of deposition and erosion in this area, we can make reasonable plans to avoid accidents.
References
- Gao Shanming et al., Formation and Sedimentary Environment of the Huanghe Delta, Science Press, Beijing , 1989.
- Chen Shupeng et al.., Application of Satellite Information to General Territory Survey, Science Press, Beijing, 1989.
- Hydrology & Hydrodynamics Lab of the Tianjing University, Marine Petroleum Engineering Environment; Petroleum Industry Publishing House, Beijing, 1983.
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