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Evolution of Yellow River Estuary from 1975 to 1986 analyzed by Remote Sensing techniques

Yuan Zhi-ping
Reconnaissance Planning & Design Institute
YRCC, MWREP China


Abstract
In order to investigate and calculate the evolution of coastline at the Y, R, estuary more than 30 Landsat images in the different time are analyzed and researched by 9 methods. This result will provide the scientific basis for the planning and development of the estuary delta.

Introduction
After the Y.R. changed it's original river course into the Bohai Sea in 1855, the swing of river channel and the flood overflow have serious influence on the development of local economy. The evolution of the Y.R. estuary is analyzed by the Remote Sensing technique to obtain the scientific basis for the harnessing and development of the Y.R. estuary and put an end to the backwardness of this region. This is the important point of the research.

Selection of Landsat images and accuracy processing
Thirty Landsat images selected from 1975 to 1986 are interpreted for the need of the research subject. The optical and computer processing of Landsat image are respectively conducted to acquire the demand information for meeting the need of the various charts. The accuracy of Landsat image depends on the varied factors. The accuracy of Landsat image, which is interpreted by the apparent ground objective method, is poor due to the theoretical and calculative error of ground objective. But the Landsat images are interpreted by the way, which make the geodetic triangulation point coincide with the apparent ground objective to obtain more satisfactory effectiveness.

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
  1. 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:


    2. 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:

    1. Same Tide Level Method for same Month (abbreviation : STLMSM)


    2. Zero Tide Level Method (ZTLM)


    3. Modified Tide Level Method (MTLM)


    4. Same Tide Level Method (STLM)


    5. Year-to-Year Mean Tide Level Method (YMTLM)


    6. Instantaneous Tide Level Method for same Month (ITLMSM)


    7. Instantaneous Tide LEVEL, High Tide Level of Large Tide and Isobath Methods .

  2. Calculation of evolution of sandspit


    3. 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.


  3. Synthetic Analyses of results


    4. The results calculated by nine methods show the following regularity:

    1. Shen xian Gully mouth to Yongfeg River (Chunrong-Shong Gully) mouth segment belongs to the forward siliting type.


    2. Shenxian Gully to Diaokoa River segment is the backward erosion type.


    3. 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  
    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

  4. Reasons for Forward siliting and backward Erosion of Coastline


    5. 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.

  5. Reasons for Forward siliting and backward Erosion of Coastline


    6. 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.

Sediment spreading in littoral area
Based on the sediment concentration in water, the Landsat images can be divided into three sediment concentration zones(2)
  1. High Sediment Concentration Zone


    2. This zone is roughly scattered over 2-3km from the coastline. Its distance from the coastline is mainly controlled by the water volume and sediment discharge transported by the Y.R. generally within the range of less than 10m depth of sea water the order of sediment content is more than 100 kg/m3

  2. Middle Sediment Concentration Zone


    3. This zone is located in 10km to 20 km from the coastline. The orders of sediment content in the upper 0.01 kg/m3 and 0.1 kg/m3 in the lower layers of sea water(3). This zone is the transition of the High sediment concentration zone to the low sediment concentration zone.

  3. Low Sediment Concentration Zone


    4. This zone is farther from the coastline. Its distance from the coastline ranges from 10km to 40km. Generally the depth of seawater is more than 10m within the range of this zone. It's orders of sediment content all are 0.01 kg/m3 in the upper and lower layers of sea water(3)
Conclusion
The application of Landsat image to the research and analysis of the evolution of coastline, the distribution of zone between tides at the Y.R. delta and the regularity of suspended sediment spreading in the littoral Zone is feasible. The information of Landsat images are increased by the various means. Because the Landsat images are analyzed in association with the conventional data and the dynamically quantitative calculation is performed based on the statically qualitative analysis, the valuable results are obtained.

In this research, the calculating methods on the evolution of coastline are newly explored this studying result clarifies some confused ideas on the evolution of the Y.R. estuary. But the researches are not enough. It requires that the subject is further investigated and studied.

Reference
  1. Li zeqang , primary Analyses of Tides along Coastline at the Y.R. Delt, Proceedings on Research of the Y.R. Estuary, research Institute of Hydraulic Science, YRCC,1983.


  2. Dai Mooching, Investigation of ocean Current in the Y.R. Estuary, Compilation of Measured Tide data at the Y.R. Estuary, Shandong Ocean University, 1984


  3. Zhao Zuein etal, Research of Spectral Features of the Y.R. water body,with high sediment content. Yellow River Remote Sensing No. 1.Jan.1981