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Poster Session
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Evolution of Yellow River Estuary from 1975 to 1986 analyzed by Remote Sensing techniques
Forward silting and backward erosion of coastline within delta area.
Tiaohe river- Yongfeng river representative coastline segment isselected from the coastline of a few hundred kilometers to research the evolution of coastline
- Calculation of Forward Salting and Backward Erosion of Coastline based on the tide characters, physical geography and engineering requirements . The representative coastline segment is divided into the following parts:
shen Xiangully -Tiaohe river segment and Shenxian gully -Youngfen river Segment
The calculation of forward silting and back work erosion of coastline is performed by the following methods:
- Same Tide Level Method for same Month (abbreviation : STLMSM)
- Zero Tide Level Method (ZTLM)
- Modified Tide Level Method (MTLM)
- Same Tide Level Method (STLM)
- Year-to-Year Mean Tide Level Method (YMTLM)
- Instantaneous Tide Level Method for same Month (ITLMSM)
- Instantaneous Tide LEVEL, High Tide Level of Large Tide and Isobath Methods .
- Calculation of evolution of sandspit
The waterway of the Y.R. was changed from the Xihekou to the Qingshui gully by man-made means in 1976 (see Fig 1) . After the new waterway of the Y.R. operated for 3 years, the sanquit, which emptied into the sea, basically had been formed in 1979 (see Fig 2). The sand spit gradually expands each year, it's present shape is shown as Fig 3 and 4. The results calculated indicate that the expanding rate of sand spit averages about 30km /year. In a hydrologic year, the forward siliting will occur during the flood period; before the flood period the backward erosion of coastline will be more than the forward siliting; after flood period the forward siliting will approximate to the backward erosion. Year by year the forward siliting gradually stretches to the Sea area.
- Synthetic Analyses of results
The results calculated by nine methods show the following regularity:
- Shen xian Gully mouth to Yongfeg River (Chunrong-Shong Gully) mouth segment belongs to the forward siliting type.
- Shenxian Gully to Diaokoa River segment is the backward erosion type.
- The coastline near the Youngfong River mouth, Diaokoa River Mouth to Tiaohe River mouth segment and coastline near the Shenxian gully mouth where the changes in forward siliting and backward of coastline are tiny. belong to the stability type.
Fig.1 Mss False colour Image of Bands 7,5 and 4 Shoiwing Evolution of Coastline (Aug. 31, 1976)
Fig.2 Mss False colour Image of Bands 7,5 and 4 Shoiwing Evolution of Coastline (Sep. 30,1979)
Fig.3 Mss False Colour Image of Bands 7,5 and 4 Showing Evolution of Coastline (Oct. 27,1983)
Fig. 4 TM False Colour Image of Bands 4,3 and Showing Evolution Coastline (Nov. 25,1985)
The trend to evolution of coastline in the delta area is that the forward silting is more than the backward erosion, the time of coastline evolution is longer than the stabilized time(see Fig 5). It can bee seen from the results calculated by means of the various methods that the same tide level method for same mouth is real and less error, its result approaches to the actual condition. However the accuracy of the zero tide method is slightly low, it can satisfy the requirements of studying work. The results calculated by several main methods are given in the flowing table.
Calculating Results of Silting and Erosion of coastline at the Y.R. Estuary
| Method Name |
Tisone River to Shenxianguly |
Shenxiangully to youngfeng River |
Total |
| Forward Siliting |
Backward Erosion |
Subtotal |
Forward Siliting |
Backward Erosin |
Subtotal |
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| STLMSH |
2.75 |
-7.48 |
-4.71 |
22.25 |
-2.40 |
19.85 |
15.14 |
| ZTLM |
2.73 |
-5.69 |
-2.98 |
28.71 |
-3.16 |
25.55 |
22.59 |
| MTLH |
0.39 |
-6.64 |
-6.25 |
22.80 |
0 |
22.80 |
16.55 |
| STLH |
1.36 |
-10.19 |
-8.84 |
50.11 |
0 |
50.11 |
41.27 |
| YMTLH |
3.49 |
-5.80 |
-2.31 |
23.95 |
-3.43 |
20.52 |
18.21 |
| ITLMSH |
2.31 |
-9.16 |
-6.85 |
18.59 |
-2.52 |
16.07 |
9.22 |
- Reasons for Forward siliting and backward Erosion of Coastline
The main reason which make the delta stretch to the sea area is the siliting of a large amount of sediment at the Y.R. Estuary. Since the ocean dynamic conditions and depositing environment of sediment are different at the various coastline segments, the rates of the forward siliting and the backward erosion also are varied. The dominative factors of backward erosion of coastline are the ocean dynamics and wind force.
- Reasons for Forward siliting and backward Erosion of Coastline
The main reason which make the delta stretch to the sea area is the siliting of a large amount of sediment at the Y.R. Estuary. Since the ocean dynamic conditions and depositing environment of sediment are different at the various coastline segments, the rates of the forward siliting and the backward erosion also are varied. The dominative factors of backward erosion of coastline are the ocean dynamics and wind force.
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