Changes in different coastal zones

First, the Yellow River Delta coastal changes

Among many factors, Yellow River sedimentation, Yellow River channel change and marine erosion play an important role in controlling the changes of the coastal zone of the Yellow River Delta.

The Yellow River is famous for its high sediment concentration and frequent channel changes. The modern Yellow River Delta refers to the section formed by the Yellow River from Tonghua cavity to Daqinghe Road at 1855. After 10 diversion, it forms an alluvial peak with Ninghai (Figure 10- 1), starting from the mouth of Taoer River in the north and reaching the mouth of branch canal in the south, with an area of about 5400km2.

1. Late Pleistocene coastal zone changes

Bohai Basin has been affected by the sea level change during the Glacier-Interglacial Period since Quaternary, especially since the Late Pleistocene, three major transgressions have occurred, which is the main influencing factor of the coastline change in this area. The first time occurred 75,000 ~127,000 years ago, with a long history of transgression, extending from the west of Cangzhou to the south of Lijin. The second time occurred 23000 ~ 3 1000 years ago, and the scope of transgression was similar to that of the first time. The third time happened 8800 years ago. In the early Holocene, the highest sea level reached 600 thousand years ago. Subsequently, the sea level gradually declined and the coastline continued to extend into the sea. By 0. 1 0,000 ~ 2,000 years ago, the coastline position was basically close to the modern coastline position.

2. Coastal zone changes since Holocene.

The formation of the Yellow River began in the Quaternary. The first generation of water system was formed in the Middle Pleistocene. After the Late Pleistocene, the Yellow River entered the North China Plain, and the upper, middle and lower reaches formed a unified water system. During this period, due to the huge swing of the Yellow River on the North China Plain, many ancient Yellow River deltas were formed. After Holocene transgression, the Yellow River entered the sea in Tianjin, and then gradually moved to the southeast. Over the past three thousand years, the changes of the Yellow River can be roughly divided into three periods, namely, from 602 BC to AD 1 128, the north of the Yellow River flowed into the Bohai Sea; 1 128 to 1855, the Yellow River and the South River flow into the Yellow Sea; 1June, 855, the Yellow River burst from the copper box and flowed back to the Bohai Sea (Figure 10-2). In the development and evolution of 140 years, the Yellow River has made a small swing migration in the south bank of Bohai Bay. Each swing forms a new delta lobe, and the leading edge of each lobe is connected to form the delta coast. Due to the downward movement of the apex of the delta, the whole delta complex moved to the sea, which led to the coastline of the delta moving to the sea. Historically, the Yellow River entered the sea in Huanghua, Surabaya, Lijin, Wudi and Dongying, forming the ancient Yellow River Delta in different periods. Among them, except Surabaya is located in northern Jiangsu, the rest are in Bohai Sea. Therefore, the evolution of the ancient Yellow River Delta is an important part of the evolution of the south bank of Bohai Bay.

Figure 10- 1 Schematic diagram of flow path change in the Yellow River Delta region

Figure 10-2 Schematic diagram of the Yellow River course change

3. Changes of the coastal zone of the Yellow River Delta in modern times.

(1) Modern Evolution of the Yellow River

During the period of1)1855 ~1889, when the Yellow River diverted to Daqing River, a large amount of sediment was deposited in the area above Taocheng Port, so there was little sediment entering the estuary, and the estuary was relatively stable. After 1872, dikes on both sides of the bank were basically formed from below the head of Dongba to 1885 and above Ninghai. With the gradual completion of dikes along the river, the sediment transported to the estuary gradually increased, and the siltation extension of the estuary began to appear. There is almost no human activity in the delta during this time.

2) During the period of1889 ~1953, the river at the tail of the estuary below Ninghai is in a state of natural change, with frequent changes. From 1890, individual farmers opened up wasteland, warlords stationed troops in 1930 to open up wasteland, and a large number of immigrants came to the delta area in 1935. At that time, only 20 kilometers long low dams were built on both sides of the strait. During the period of 1940 ~ 1947, the Yellow River briefly changed its original southern line and entered the Yellow Sea. After 1947, the Yellow River returned to its current channel, and the local government in the liberated areas carried out dike construction in four phases, with the left and right dikes extending to "Four Sections" and "Songjiaquan" respectively, with a length of about 30 kilometers. During this period, the tail reach below Ninghai, with Ninghai as the apex, swings for 6 times, and the Yellow River Delta fan pushes towards the sea 15 ~ 20km.

3) 1953 to 1976 With the establishment of new China, the production and construction in the estuary area are developing continuously, and the flood control requirements are increasingly urgent. It is not allowed to change the flow direction of the tailrace at will. In particular, in 196 1 year, oil exploitation began in the Yellow River estuary. In order to protect the industrial and agricultural production and flood control in the estuary area, a series of treatments have been carried out in the estuary reach, including heightening the Yellow River levee by more than four sections and widening the reach with serious water blockage and ice jam. In order to ensure the development of the delta oil field, production dikes on both sides of the river were built below the fourth section, and three artificial diversions were carried out in three river sections: 1953, 1964 and 1976 in a planned way, and the sand outlets were reasonably arranged, so that the modern delta sector was extended by15 ~ 2,200 km2. The above measures have played a good role in ensuring flood control safety in the downstream Xihekou area.

4)65438-0976 is the current operation period of Qingshuigou flow path. In order to adapt to oilfield development and local industrial and agricultural production, the dikes on both sides of Qingshuigou channel have been raised since 1976, and some control and diversion projects have been built between 1 and 7/to stabilize the river regime. The diversion dike has been built below the 7th grade, and after 1980, a new river course is basically formed, and the river course with concentrated water flow is smooth. Since 1988, a series of local regulation measures have been taken in the reach near the estuary to keep the estuary flow path stable to this day. Accordingly, a new estuary coastline is formed, which generally extends outward, and the longest part is 30km longer than 1976.

(2) The evolution of the coastal zone in Diaokou section.

Since 1976 the Yellow River diverted to Qingshuigou, the coastal area of Diaokou River area has been shrinking. 1976 before the diversion of the Yellow River, the sand mouth was in an extended state, and the extension rate was about 1.5km per year. After the diversion, the sand mouth and the nearby coastline are in a state of erosion. From 1976 to 1984, the sand mouth was eroded by 3.2km, with an average of 0.4km per year. In 1985 ~ 1996, the sand mouth * * eroded 202km2, of which 1985 ~ 199 1 eroded 98km2,199199. 1985 ~ 1996, the maximum erosion section rate of coastline reaches 900m/a, generally 300 ~ 400 m/a, 1996 ~ 2004, * * erosion 162.564km2, without human activities. However, this kind of siltation is different from that of flowing rivers. The coastal siltation of the flume is an extension of the siltation driven by the sand mouth, and the extension range is related to many factors such as incoming water and sediment. Coastal siltation under human disturbance is a parallel extension of the whole coastline, regardless of active or passive, and the extension is decreasing (Figure10-3; Photo 10- 1 ~ photo 10-3).

(3) The evolution of the coastal zone in the port section of the Yellow River.

The Yellow River Port was built in 1985, near the tidal point of M2. Before the port was built, the coastline near the harbor was always in a state of erosion from 1975 to 1976 without diversion of the Diaokou River. From 1976 to 1984, due to the large-scale erosion of the coastline near Diaokou River, part of the sediment was brought to this area under the action of ocean dynamics, which caused the deposition of the coastline in this area. 1985 After the port was built, due to the protruding tidal breakwater in the port, the marine dynamic function on the left side of the port was strengthened, and the coastline was in an erosion state; On the right side of the port, the coastline is in a state of siltation and extension (Figure 10-4). Because the erosion on the left side of the port affected the safety of the port, 1986 built a dampproof dike similar to a dam there to prevent the erosion of the left coastline of the port. But it was washed away by the spring tide soon after it was built, and then a moisture-proof dike was built in the left erosion section of 1987. In addition, after the completion of 1988 Zhuangxi Oilfield, the coastline (based on the general high tide line) is basically fixed. At the same time, the coastline on the right side of the port changed from siltation to erosion, but the erosion rate was not large. Considering the safety of the port, 1990 (photo 10-4) built a general protective dike about 2km long on the right side of the port, which basically controlled the erosion of this coastline. The coastline has not changed since 1990.

Figure 10-3 1986 ~ 2004 coastline change map in diaokou area.

Photo10-11991year remote sensing image of diaokou area.

Photo 10-2 1996 remote sensing image of diaokou area.

Photo 10-3 remote sensing image of diaokou area in 2000.

Photo 10-4 Protection dike near Yellow River Port

Figure 10-4 1986 ~ 2004 coastline change map of the Yellow River port section.

(4) Evolution of estuarine coastal zone

During the period of 1976 ~ 198 1, the clear water channel has not formed obvious sand mouth, but it is still swinging, but the sand mouth has been silted and extended. During the period of 198 1 ~ 1984, the sand mouth was obviously silted eastward, and the siltation speed at the estuary reached 5km/a, with an average annual reclamation area of about 5km2 (Figure 10-5). During the period of 1985 ~ 199 1 year, the change of sand mouth was relatively stable, and the deposition rate was about 2.4km2/a ..1991~1996, which obviously accelerated. After the average sedimentation rate of 1985 ~ 1996 reached 12. 1km2/a, 1996, the Yellow River entered the sea artificially from 1 north branch, which changed the sediment. This is mainly because Shengli Oilfield took artificial measures to exploit the sea.

Fig.10-51976 ~1984 change map of estuary coastline.

Figure 10-6 1986 ~ 2004 coastline change map of the estuary section.

The extended erosion of the sand mouth is closely related to the incoming water and sediment, that is, the extended length of the sand mouth is positively related to the water-sediment ratio (the ratio of incoming sediment to incoming water). The larger the water and sand, the longer the extension length of the sand mouth; When there is relatively little incoming water and sand, the extension of the sand mouth is less, and even erosion will occur.

The coastline near Shazui in different years was extracted from remote sensing images, and the coastline of estuary was intercepted by ArcView function of GIS software, and its evolution was compared and analyzed.

The overlay analysis of RS image information by using GIS technology shows that during the period of 1976 ~ 198 1, the flow path of Qingshuigou has not formed obvious sand mouth, but it is still swinging, but the sand mouth has been silted and extended. 198 1 ~ 1984, the sand mouth is obviously silted eastward, and the siltation speed of the estuary reaches 5km/a, with an average annual reclamation area of about 5km2. During the period of 1986 ~ 1987, the change of the sand mouth is relatively stable, and the sedimentation rate is about 2.4km2/a. Since 1988, the sedimentation rate of the sand mouth has obviously accelerated, making the average sedimentation rate from 1985 to 1995 reach. Between11907' ~1910', the south side of the sand mouth was scoured during the statistical period, and correspondingly, the north side of the sand mouth was rapidly silted. Cause analysis: During the flood season of 1979, the sand mouth swung from southeast to northeast. Scouring on the south side shows that by 1992, the coastline of this sea area has not reached the entrance position before diversion; Near the new entrance formed after the swing, due to the shallow water depth in the sea area, the entrance will be in this area in the next few years, and the reclamation rate on the north side is relatively high, and the reclamation scope is also concentrated in this area. It can also be seen from Figure 10-6 that the sedimentation on the north side is getting smaller and smaller along the latitude direction, and the sedimentation on the south side is more uniform, which is related to the topography, tidal current characteristics, sediment diffusion direction and other factors in the sea area near Shazui. As far as the whole sand mouth is concerned, the more the sand mouth extends to the sea, the smaller the siltation area is, which is consistent with the actual situation of the estuary.

From the comparison of remote sensing image information in each year, it can be seen that the sand mouth of Qingshuigou channel changes sharply and has a wide range. From the change of the whole coastline, it can be preliminarily considered that there is a law of large short-term amplitude and small long-term amplitude. That is to say, on the one hand, the interannual variation is great, and the siltation and erosion of the sand mouth can reach 5km in one year. On the other hand, the variation range in long series years is small, and the annual average siltation is about 65438±0km.

In addition, from the remote sensing image information since 1976, it can be known that the change characteristics of the north and south sides of the sand mouth in Qingshuigou channel are as follows: 1976 ~ 1984 is the main siltation period on the north side of the sand mouth, and the coastline near Gudong Oilfield advances and retreats, but mainly retreats, and the south side of the sand mouth is eroded during this period. From 1984 to 1988, the coastline on the north side of Shazui was eroded except the coastline near Touhe Gudong Oilfield. The south has been silted up. At 1988 ~ 1996, except for the head, other parts on the north side of the sand mouth are deposited evenly; The south side is still in the siltation stage of the whole line. The general trend is that the sand mouth silting body gradually advances to the sea area with the extension of the sand mouth.

There is an approximate linear relationship between the siltation and erosion of the front end of the sand mouth and the reclamation area near the sand mouth, that is, the siltation and extension of the front end of the sand mouth drive the siltation of the coastline near the sand mouth, and the net reclamation area of the whole estuary area increases, and the speed of siltation and extension determines the size of the net reclamation area. On the contrary, the retreat of the front end of the sand mouth will lead to the erosion of the coastline on both sides, and the speed of retreat will affect the speed of erosion.

Second, the changes in the coastal zone on the south coast of Laizhou Bay.

At the beginning of Holocene, with the rapid rise of sea level, the coastline quickly advanced to land and reached the vicinity of Xiyou on the east coast of Laizhou Bay. After this transgression, regression occurred about 8000 years ago. Near the west of the east coast of Laizhou Bay, the coastline recedes at least 1 1m below the modern water depth. From 7300 to 7000 years ago, the coastline advanced near the modern coastline. By about 6000 ~ 5000 years ago, the coastline continued to advance to the maximum extent on land. During this period, the coastline was clear and clear, and it went deep into the land along the coast of Laizhou Bay for more than 30 kilometers. But on the coast of bedrock harbor, it is roughly consistent with the 5m contour line. After the maximum transgression, the coastline began to retreat about 4500 years ago. The sea level fell below the modern sea level 4000 ~ 3000 years ago, and the sea level fluctuated slightly above and below the modern sea level since 3000.

Third, changes in the coastal zone of Jiaodong Peninsula

1. changes of coastal zone since late Pleistocene

Around 12000, the sea level rose sharply, causing large-scale transgression. As the sea level rises, seawater gradually invades inland areas. 8,000 years ago, seawater further invaded the present coastal valley plain, reaching 5-20km inland and reaching Li Xiaozhuang, Yinghai and Yangheya in Jiaoxian County on the west coast of Jiaozhou Bay. In the Dagu River valley, it invaded inland for more than 20 kilometers and reached the Ji Jiao railway line south of Lancun. 6000 ~ 5000 years ago, at the peak of transgression, seawater flooded the coastal land below 5 meters above sea level, forming two ancient estuaries, such as Mawan and Dingziwan in Dagu River. At that time, the sea level was 2 ~ 3 m higher than the modern sea level, and a high sea level appeared. From 4000 to 3500 years ago, the sea level showed a downward trend. With the accumulation of terrigenous sediments, the sea water retreated from the estuary and the sea level fell back to the modern sea level. Due to the influence of marine invasion, some coastal areas were submerged by seawater, and seawater was reinjected along the river, which expanded the water area and raised the groundwater level. About 10000 years ago, the sea level in the east of China had risen to-28m, and its rising speed was very alarming. The marine environment expanded to the land direction, and seawater flooded the early swamps and forests, turning rivers into flooded valleys. About 8000 years ago, mankind suffered the second great flood since the Neolithic Age. In the following 1000 years, the sea level rose by 14m, that is, the sea level was -4m 7000 years ago. Since then, the sea level rise has slowed down, but it has not stopped. By about 6000 years ago, the sea level had risen to a height of 2-4 meters higher than the current sea level.

Coastal micromorphology is the product of neotectonic movement, which can be used to analyze the changes of land and sea since Holocene. In Jiaodong Peninsula, there are mainly ocean terraces and ocean cliffs. Ocean terrace includes first-class ocean terrace and second-class ocean terrace. The typical profile of the secondary marine terrace is located on the east bank of Dazhushan, with the terrace height of 10m and the terrace width of 0.5 ~ 1km, indicating that the ancient seawater intruded about 0.5 ~ 1.5km and then retreated. In modern times, it was invaded again, about 0.5km away from the modern coastline, and the sea water retreated to the modern coastline again. Hongshiya is the most typical compound area between the second terrace and the first terrace. The second terrace near Hongshiya is 10m in height, 0.25~0.5km in width, 5m in height and 0.5km in maximum width, which indicates that the seawater has advanced and retreated many times in this area after the Pleistocene, and finally the seawater retreated to the modern coastline.

Marine cliffs are mainly distributed in the south bank of Laoshan, Xuejia Island, Dazhu Mountain, Shijiacun Village and Lingshan Island, among which there is an underwater cliff with a depth of 19m near Laoshan Head. The transgression in the early Holocene once reached the north of Lancun village in Jiaozhou Bay, with a depth of 30 kilometers. Laizhou Bay in the north invaded the Xinhe area, and the depth of crossing the Xinhe River was about 3.5km.

2. Modern coastal zone dynamics

(1) Overall change trend of coastal zone

From 1950s to 1980s, the total land area showed an increasing trend, mainly in the Gulf region, which was caused by artificial dams, harbor works, salt fields and shrimp ponds, followed by river siltation, which was the dominant trend of land and sea growth in Jiaodong Peninsula at this stage. Due to the growth of the inland area of the bay, the curve radian of the coast becomes smaller and the coastline tends to shorten; However, the increase of salt fields makes the coastline change from straight line and arc line to broken line, which increases the length of coastline; The transformation of the island into a peninsula has also increased the length of the land coast.

Beaches protruding to the southeast often recede and narrow due to impact, while low-tide beaches in the bay are mostly widened. The low tide beach at the outlet of a big river is often greatly influenced by river scouring and ocean currents. On the whole, the 5m isobath of Qingdao has little change, and the isobath beyond 10m tends to move to the land, and the seawater gradually becomes deeper. Due to the influence of artificial engineering, the island near the land has become a peninsula, and the land area has increased. However, the vast majority of islands far away from land have shrunk in area, split in two, and even become reefs at low tide, with low-altitude islands being the most prominent. This is because the sea level rises due to transgression, which partially or even completely submerges the island, and the transgression is very obvious.

From 1980s to 2000, the land area of Jiaodong Peninsula continued to grow due to artificial land reclamation. For example, along the northern coast of Jiaozhou Bay, the land growth is mainly based on building dikes to build salt pans, which are pushed to the sea by about 1km, and the salt pans and seawater farms along the coast of Hongdao are also increased, widening by about 200-500 m. At the place where Licun River enters the sea, the low-tide silt beach, which was originally about 3km wide, has become a part of the land because of artificial reclamation, and the land between Licun River and Nvgu Mountain is pushed to the sea by about 0.5 because of reclamation. Due to artificial reclamation, the land area of Huangdao area has greatly increased. Its north-south width increased from 1.5km in 1980s to 2.5km in 2000, and the land width between the north and south coasts of Haowa increased sharply from 2km to 4.5km.

Since the 1980s, the overall land reduction is not obvious, because salt fields, seawater farms and artificial reclamation cover up the erosion of land by seawater intrusion. During this period, the general trend of coastline change is to push towards the sea. Due to the increase of land area, the radian of bay arc decreases correspondingly, and the length of coastline is slightly shortened. Moreover, because most of the artificial projects such as salt fields, seaports, docks and farms extend into the sea, the length of the coastline has increased slightly. Generally speaking, the total length of coastline has not changed much.

(2) Human engineering activities are the main factors of coastal changes.

The main utilization methods of tidal flat are artificial reclamation and aquaculture, and the main hazards of dynamic change of coastal tidal flat are:

1) Blindly reclaiming land from the sea, competing for land with the sea, destroying the hydrodynamic environment and ecological environment of the original Xiaowan, leading to beach displacement and unbalanced ecological balance.

2) The intensification of marine pollution makes beach resources lose their use value; Blindly expanding the aquaculture area, aquaculture wastewater has a negative impact on marine life and ecological environment in tidal flats. The environmental quality of some sea areas has declined, and industrial wastewater and domestic sewage have exceeded the standard. Eutrophication of water bodies in some sea areas makes the ecological environment of beaches worse and worse.

3) The hastily constructed marine engineering without scientific demonstration has caused irreversible changes in local marine and hydrological conditions, and often brought unexpected environmental damage.

With the enhancement of people's awareness of environmental protection, living in harmony with nature has gradually become people's understanding, and the control of various geological disasters, the prevention of seawater pollution, the prevention of seawater (salt water) invasion, and the rational utilization of coastal beaches will gradually be put on the agenda.

Sea sand is an important marine mineral resource. The buried sand body in Qingdao Qianhai, Jiaozhou Bay is an ancient sand dune formed 10000 years ago, which is an important non-renewable natural resource. Large-scale mining of sea sand will bring a series of new environmental disasters. If the thick beach near Qianhai is excavated, the underwater bank slope in dynamic balance will move and collapse, which will eventually lead to beach erosion, and the erosion intensity is about 40cm per year. The most serious consequences may lead to the gradual disappearance of a large area of beaches and the re-emergence of reefs. 1993 Long Island burst its banks, 200 houses collapsed, and all farmland in two natural villages was destroyed due to excessive dredging. For the same reason, part of Rizhao coastline has retreated 100 meters ... In addition, if sea sand is exploited in Jiaozhou Bay, Qingdao, the economic loss of natural fishery resources will exceed 6.5438+0.8 million yuan, which will also lead to the extinction of amphioxus, a national second-class protected animal.