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Poster Session
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Satellite observation of south coast of Bohai Bay
Deposition and erosion along the south Bohai Bay Coast
Deposition and erosion are various from place along the south Bohai Bay coast. we therefore divide the coast into two segments: one from the Tiaohe river to west, and the other from the Taiohe river to east.
- West Segment
This segment belongs to weakly retreat-by - erosion type coast, extending from the Taoer river to the Tiaohe river 9 Fig. 1). The Huanghe river emptied from this segment into sea from 1904 - 1926. After then, retreat-by-erosion environment has developed Because of the long period of stagnant, and retreat rate has become lower.
This segment can be still subdivided into two parts: from Walagou to west, the beach is broad and gentle, its maximum width being up to more than 20 k, and its slope only about 1:10,000; from Valagou to east, the beach width is about several kilometers and slope about 4:10,000. along the western part, tide difference is larger, and storm surge effect is obvious, retreat mainly results from tide and wind effects.
The high tidal boundary , therefore , has strongly gone back. according to the theoretical zero-depth contour from 1975 to 1985, the low tide zone has widened , demonstrating that the coast became gentler and wider by erosion and retreat. The resultant coast topography will reduce erosion and tend to make the coast stable.
The eastern part has been influenced by sludge supply by the Huanghe River from 1974 to 1976, and has propagated with silting up. Since then, eastern part has retreated by erosion and showed the common development trend with the western part, but to a lower degree. Retreat of erosion cliff displayed in the satellite images before 1980 and after 1983 shows that the high tide zone went back slowly. The theoretic zero depth contour shows that the retreat rate changed with time (Fig. 2) and reached up to maximum from 1978 to 1980, become lower in recent years.
Fig. 1 A diagram showing deposition and erosion along the south Bohai Bay Coast
Fig. 2 A diagram showing propagation and retreat rate.
- East Segment
This segment, extending from the Tiaohe River to the Wuhaohuang, belongs to strongly retreat-by-erosion type. The Huanghe River emptied from this segment into sea for three times from 1926 to 1929. Because of the latest stopping of water current and short stagnant period, retreat-by-erosion is strong and retreat rate along the whole segment is larger than that along the west segment.
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Image 1. | Obtained , May 22, 1975.
The tide level is lower than the mean sea level.
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Before the 1975 flood season coming, the river mouth is smaller.
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Image 2. | Obtained, Dec. 17, 1976.
The tide level is lower than the mean sea level, the tide situation is
similar to image 1. |
After undergoing the 1975 flood season, coast -line changed evidently Towards sea the river mouth is in convex bank.
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Image 3. | Obtained, April 2, 1981.
The tide level is lower than the mean sea lovel, the tide situation is similar to both image 1 and image 2. |
Since the huanghe River channel changed its direction in 1976, the erosion caused the shape of the River mouth changing evidently
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Image 4. | Obtained, Nov. 25, 1995.
The tide level is lower than the mean sea level, but it is little lower than image 1, 2, and 3. |
| Erosion caused the coastline changing in more smooth shape. |
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