Study on Coastal Transformation and Its Environmental Geology in Southern Fujian Province

Lin Jun

(Fujian Provincial Institute of Geological Survey, Fuzhou 350003)

Abstract: Coastal erosion and siltation are the main factors in transforming the coastal geologic environment, and in the current general situation of the world's rising sea level, coastal erosion will become the most important natural disaster in the global coastal zone, and the siltation of the bay is affecting the sustainable development of the port city. The use of remote sensing technology and spatial and temporal comparative analysis and other monitoring means to reveal such profound changes in the geological environment, as well as the objective impact on the living environment of human beings, is a hot and difficult issue for future research in environmental geology. On the basis of systematically summarizing the characteristics of modern coastal geology and geomorphology, and the overview of coastline changes since the Holocene, this paper discusses the current situation and development trend of coastal changes in the coastal areas of southern Fujian, and puts forward the relevant environmental geology problems and prevention and control countermeasures.

Keywords: coastal change; coastal erosion; bay siltation; environmental geology; southern Fujian

1 Modern coastal geology and geomorphology

The coastline of southern Fujian coastal area is generally spreading in the NE-SW direction, and the coastline is winding and meandering, with a total length of about 1327.5km (including 347.8km of island coastline). The total length of the coastline is about 1327.5km (including 347.8km of island coastline), among which, the length of artificial dyke is 450.0km, accounting for 33.9% of the total length of the coastline. The geological structure of this area is complex, NNE and NE direction of the main fracture control the spreading orientation of the coast, NW direction of the tensile fracture and the former composite part, the development of bays, Hong Kong and Macao. The coastal landforms are dominated by rounded low hills, laterite terraces and estuarine plains. The coast is characterized by headlands and bays, low hills and plains. The bedrock of the coastal zone includes Jurassic-Cretaceous volcanic rocks, Yanshan-age granites, Upper Triassic-Jurassic metamorphic rocks and Upper Tertiary basalts, with strong weathering of the rocks; in the estuaries and harbors, the loose accumulations of the Fourth Series are more developed. According to the cause of the composition of the coastal lithology, morphology and resistance to erosion, the coast of the region can be divided into bedrock coasts, sandy coasts and silty coasts of three major types.

1.1 Bedrock coast

Bedrock coast is mainly distributed in Hui'an Chongwu, Jinjiang Weitou, Longhai Liuhui, Zhangpu Liu'ao and Gulei, Zhao'an Gongkou and other peninsular areas. In these sections due to the coast directly suffered from the strong erosion of seawater power and the abrasion of the shore current, the phenomenon of sea erosion is developed, and there is almost no beach accumulation. Bedrock coasts can be further divided into rocky (fresh bedrock) coasts and weathered shell coasts according to the degree of weathering and the strength of erosion resistance.

1.2 Sandy coast

Sandy coast is mostly formed in the coastal low hills or bedrock promontory between the inner side of the open bay, such as Hui'an Dagang, Jinjiang Shenhu Bay and Weitou Bay, Longhai Harbor and Longjiao Bay, Zhangpu Foutou Bay and General Bay, Dongshan Wujiao Bay, Zhao'an Dacheng Bay, etc., along the coast of the sandbanks, sand dams, sand spit, the development of sea into the terrace landforms and the plains, the shoreline is relatively straight.

1.3 Silt coast

Silt coast is mainly distributed on the top of wide bays, and the area where rivers enter the sea, according to its material source and geographic location can be divided into harbor type and estuary type.

(1) harbor type: mainly distributed in Meizhou Bay, Xiamen Harbor, Zhangpu Old Town Bay, Dongshan Bay and Zhao'an Bay. These harbors and bays *** same characteristics are: land area surrounded by low hills or terraces, the mouth of the bay is often a barrier of islands, often the bay in the bay, semi-enclosed; therefore, the wave action is weak, the shore slopes are low and slow, and the mudflats are open. Its material mainly comes from the surrounding bedrock weathering crust, transported by temporary surface water flow or coastal currents, tidal currents, waves and other transport, deposition. According to the field survey, the harbor-type silty coast in southern Fujian is still in the state of filling and silting up.

(2) estuarine: mainly distributed in the mouth of the Jinjiang River and the mouth of the Jiulong River and other large rivers on both sides of the bay, often forming a wide estuarine silt plains. These plains are broken in the sinkhole basin in the drowned valley estuary long-term river, sea and other external power interaction, gradually backfill development and become, flat topography, a single type of geomorphology, most of the current in the silt up.

In the harbor, the estuary of the beach wetlands, there are often sporadic, piecemeal distribution of mangrove forests, at present better protected mainly in the Dongshan Bay, Zhangjiang River mouth Jhuta and the mouth of the Jiulongjiang River, Cao Pu Tou. Mangrove forests have the functions of promoting beach siltation and windbreaks, as well as purifying seawater; it is recommended to strengthen the management and protection of the existing mangrove coasts, and artificial planting can be carried out in certain eroded shore sections to improve the geological and ecological environment of the coastal zone.

2 Overview of coastal changes since the Holocene

2.1 Early Holocene (12000～8000a, B.P.)

The climate began to warm up, and with the melting of the global late Quaternary glaciers, the sea level rose substantially and continuously. From 12,000 to 9,500a before present, the coast was again subjected to sea invasion, the average sea surface elevation was about -11.0m (Yellow Sea Elevation, B.P.), the coastline was slightly more easterly than at present, and around 8,000a before present, the sea level fluctuated slightly again.

2.2 Middle Holocene (8000-2500a, B.P.)

The climate continued to warm, and the sea level oscillated at a high level. About 7500 years ago was the biggest sea invasion in the Holocene, the sea surface elevation could reach 5.0-10.0m, the seawater invaded the inland along the river, and the shoreline was located several kilometers to tens of kilometers to the west of the present coastline; about 6000 years ago, due to the differential elevation movement of the new tectonic fault block, all the seawater of the shoreline section was withdrawn, and the average low sea surface elevation was about -5.0m. Subsequently, about 5400~3100 years ago, the sea surface elevation was about -5.0m. ~ 3100 years, the sea level began to rise again, the high sea surface elevation of about 4.0m, stable for a long time, the development of peat layer and shell dykes in the land-sea interface zone, the ancient coastline than the present slightly to the west; since then a small-scale sea recession has occurred.

2.3 Late Holocene (since 2500a, B.P.

This is a recent period of riverbed evolution and mudflat development, the regional sea level is basically stable, but there are local problems of rise and fall, and the last recession took place about 1400-700 years ago. It can be seen that although the Holocene is a sea advance, but not a linear rise, but there are many times the process of sea level fluctuation and shoreline change (Table 1, Figure 1). Historical records and test data indicate that most of the coastal plains in the region were formed in the last thousand years. The Quanzhou Plain was formed by gradual accumulation after the Ming Dynasty (1368); the Longhai Plain, according to the 14C dating analysis of the surface layer of Shatou Farm, is about 600 years old. In Jinjiang Shenhu Bay (1987), Zhangpu Qianhu Bay (1999), Dongshan Maluan Bay (2001), and Shishi Shahu Bay (2005), remnants of primitive ancient forests have been found in the intertidal zone, suggesting that there is a recent upward trend in the sea surface, and that the coastline is still in the process of development and evolution due to the different geologic environments of each shoreline section, the differences in the effects of internal and external dynamics, and the influence of anthropogenic factors.

The coastline is still in the process of continuous development and evolution.

Table 1 List of Holocene paleo-surface markers and 14C dating along the southern coast of Fujian

Continued

Figure 1 Schematic diagram of Holocene paleo-coastal variability along the southern coast of Fujian [6]

3 Analysis of the current status and trend of the coastal variability

3.1 Changes in sea level

Coastal variability is a comprehensive reflection of the rise and fall of the sea and land levels. The coastal change is a comprehensive reflection of the rise and fall of sea level and land. In recent years, scientists from various countries have constantly warned that the destruction of the atmospheric ozone layer due to the greenhouse effect caused by carbon dioxide and the massive use of chlorofluorocarbons (CFCs) in the industry has led to global warming, and the temperature of seawater and sea level are on an upward trend. The information released by the State Oceanic Administration and the long-term monitoring data from dozens of marine observatories and tide gauges in China show that sea water temperature and sea level in most of China's coastal waters are on an upward trend. Especially since the 1960s, the global seawater temperature has gradually increased, and the sea level has risen by an average of 14.4 cm over the past century, with an average rise of 11.5 cm along the southeastern coast of China, which corresponds to an average annual rise rate of 1.15 mm/a, and the predicted rate of rise along the coast of Fujian can be as high as 2.0-4.64 mm/a. Xiamen has risen by 10.54 cm over the past 30 years with an average rate of rise of 3.40 mm/a, and the average rate of rise of 3.40 mm/a.

3.2 Land crustal changes

The background of land crustal deformation in this region is mainly affected by the collision of the Philippine plate and the Eurasian continental plate, under the action of the NWW oriented geostress field, the NW disk of the southern section of the NE Zhenghe-Daipu-Shenzhen rupture is in a downward trend, and the SE disk is in an upward trend; therefore, the overall characteristics of the crustal deformation appear Therefore, the overall deformation of the crust is characterized by inland to coastal and north to south tilting. Due to the activity of the rupture, there are still localized relatively downward sections in the NW fault depression, such as the vicinity of Zhangpu and Dongshan Bay. According to the observation of the seismic department, the amplitude of crustal deformation (interval of 8.55 years), the northern Hui'an, Jinjiang is +30～＋20mm, the rate of rise 3.51～1.71mm/a; to the south of Zhangzhou, Xiamen is +25～＋20mm, the rate of rise 2.92～1.71mm/a; and to Zhangpu, Dongshan is -10～ -30mm, the rate of decline 1.92mm/a; to Zhangpu, Dongshan is -10～ -30mm, the rate of decline 1.92mm/a. There are other supporting evidences for the obvious downward trend along Dongshan Bay: there is a stone monument carved on the bedrock during the Wanli reign of the Ming Dynasty in Chencheng Town on the southern part of Dongshan Island, which has now been buried by marine sand; the tidal dyke built in the 1960s at Xipu in Chengguan has long been scrapped; and according to the fishermen of Aojiao Village, the residential houses above the high-tide line can now be flooded by high tides. According to the fishermen in Aojiao Village, the houses above the high tide line can now be flooded to a height of about 1.0m; Dongshan County fishermen in the waters of Brothers Island continue to salvage bricks, tiles, as well as deer, bears, and other large vertebrate skeletons; Dongshan County, "sinking of Tokyo," the legend of the county records, reflecting the other side, the ancient people who lived in the area, but also felt the coastal changes and the changes of the sea. The change of the sea and the change of the sea.

3.3 Changes in the coastline

The sea level rise potential of the region has different manifestations in different parts of the region. Macro, for the crustal deformation of the upward trend of the lot, because the crustal rise speed and sea level rise speed is basically equal, so it is relatively static, sea level rise on the region is relatively weak; for the crustal deformation of the downward trend of the lot, because the crustal fall speed and the sea level rise speed is basically equal, and the two superposition of the sea level rise speed doubled, can be up to 4.0 ~ 10.0mm / a, making significant changes in the coastline. a, causing significant changes in the coastline and posing a serious threat to coastal areas. Microscopically, as the rise and fall of the coastal land area, sea level change, and oceanic and estuarine dynamics tend to be intertwined, the coastline of each section of the work area from the north to the south of the coast varies in advance and retreat. Now, through the measured topographic maps (1959-1981) and remote sensing means (1986-2000), and based on the change of the zero-meter line of the Yellow Sea elevation, the type of coastline change in the southern coastal area of Fujian is classified into three types: erosion and retreat coast, silt uplift coast, and stabilization (equilibrium) coast.

(1) Erosion of the coast: open sea islands, peninsulas or headlands, perpendicular to the waves of the shore section, the bay on the side of the wind and waves, etc., can be directly subjected to wind and waves, tides, strong erosion. About the size of the coastal erosion rate, in addition to the strength of the external power geological action, but also by the composition of the coastal lithology control. Rocky coast is more resistant to erosion, the erosion rate is slow, it is not easy to notice the changes in the short term, its form is mostly steep cliffs or underwater rocky beaches, mainly distributed in the northeastern and southern islands and peninsulas, such as Chongwu Peninsula ballast, Zhenhai - Liuhui Angle, Dongshan Island Ao Angle, etc.; Strongly weathered - highly weathered weathered crust coast is relatively poorer in resistance to erosion, and its form is often steep or upright, and its form is often a little more than a few feet. Morphology is often steep or upright shape of the sea erosion of soil cliffs, due to strong erosion by the wave camp force is constantly being flattened, often forming a pile of sandy beaches or sandy shores, such as Nan'an Shijing Qiaotou, Shamhou Guianliao and other places.

Because of artificial reclamation or sand mining and other engineering activities, resulting in the interruption of the source or insufficient supply of sandy coast, the phenomenon of erosion is also more prominent. Such as around the head of the Bay East Shita head area, sandy coast originally belongs to the slight rise or basic stability; but since 1956, due to the coastal cove estuary building gates, reclamation, coupled with a large number of man-made sand dredging, resulting in the interruption of the sediment into the sea, insufficient recharge of the material source, the coast is strongly erosion. In the past 20 years, the coast erosion 20.0 ~ 80.0m, high tide beach erosion low 0.50 ~ 1.0m, coastal sand dike erosion exhausted, has been built stone dike and other shore protection projects have also been repeatedly destroyed. The rate of change of zero meter line of representative eroded coast in the area, see Table 2.

Table 2 Statistics of the rate of change of zero meter line of eroded coast in the southern coastal area of Fujian

The cumulative total of eroded coast in the whole area is about 445.0km, which accounts for 33.52% of the total length of the coastline, and it mainly distributes in the strongly weathered - drastically weathered bedrock coast and sandy coast.

(2) Silt up coast: mainly distributed in Quanzhou Bay, An Harbor, Tong'an Bay, Xiamen Harbor, Old Town Bay, Dongshan Bay, Zhao'an Bay and Gongkou Harbor. Harbor-type silt up coast, mainly distributed on both sides of the peninsula and the southwest side of the island, this type of bay, although no rivers carry a lot of sand into the bay, but because of the recent rise in the sea, the tide is fast, slow ebb and other hydrodynamic conditions of control, so that the shore current and waves brought by sediment due to the weakening of hydrodynamics and the production of piling up, especially in the belly of the mouth is small and the coast of the bay of the slope of the gently more conducive to siltation, those rich sources of material in the Bay will gradually into the land, the zero-meter line to the mouth and shallow sea, the bay will gradually become land. The meter line expands to the mouth of the bay and the shallow sea. Estuarine siltation bank, due to the rich source of sediment, hydrodynamics is weak, the beach surface is wide and gentle, the composition of the material is fine, has a very favorable depositional environment, the zero-meter line siltation rate of up to 10.0 ~ 100.0m / a, accumulation rate of 5.0 ~ 30.0cm / a.

In addition, the enclosure of the sea to make fields, blocking the bay to intercept the flow, repair dykes to build the gate, and other coastal engineering activities, objectively impede the flow of the smooth flow, reduce the amount of tide, prompting the sea to build a new river, and the sea is not a good place. Such as Quanzhou Bay Luoyang River mouth section, from 1972 onwards, one after another in Luoyang Bridge to build gates, with the "May 1" reclamation, east of the city reclamation and Baisha reclamation projects implemented one after another, so that the area of the tidal area of the corresponding reduction of more than 1:3, resulting in slowing down the flow rate of the waterway, a large amount of siltation of sediments, tidal flats continue to silt up the waterway is seriously silted up. From 1969 to 2000, Houzhu port zero-meter line on both sides of the waterway to promote the total sum of 780.0m, an average of about 25.16m / a. District silt coast zero-meter line to the outward push changes, see Table 3.

All the region's silt coast cumulative total of about 560.0km, accounting for the total length of the shoreline of 42.18%. Among them, 360.0km of shoreline is in natural siltation state, and 200.0km of shoreline is in siltation due to coastal engineering, accounting for 35.71% of the total siltation length of the shoreline.

(3) stable (balance) coast: refers to a long time, the coast of the dynamic changes in the wash and siltation of the basic balance; or the original erosion of the coast, now take engineering or biological protection measures, the shoreline basically tends to stabilize. Bedrock stabilized coast, generally distributed in the topography of more hidden harbor; sandy stabilized coast, mainly distributed in the direction of wave action and parallel or nearly parallel to the open shore. Such as the southern part of Shenhu Bay, sandy coast, despite the obvious seasonal changes, the local phenomenon of siltation; but outside the shore of the deep water flow, material sources are relatively limited, perennial scouring, siltation dynamics are basically balanced, the shore remains stable.

This area has a total of about 322.5km of stabilized shore, accounting for 24.29% of the total length of the shoreline. Among them, the natural siltation balance shore section is 72.5km long; after taking engineering reinforcement measures, the siltation balance shore section is about 250.0km long.

Table 3 Statistical table of change rate of zero-meter line of siltation coast in southern coastal area of Fujian Province

4 Coastal change of environmental and geological problems

4.1 Coastal erosion and retreat jeopardizes the safety of coastal residents and infrastructure

The current general situation of the world's rising sea level is that the sea level of the world is rising. current general situation of the world sea level rise, coastal erosion will become the most important natural disaster in the global coastal zone. With the intrusion of seawater, coastal scouring, erosion retreat, often destroying coastal roads, embankments, cables and other infrastructure, threatening the safety of ports, wharves and other shoreline projects, exacerbating the siltation of harbors, affecting the economic development of coastal areas.

(1) Fujian coast every year there are strong typhoons landfall, tsunami, wind and waves, tides and other external power effects, strong erosion of the coast around Xiamen University, there are hundreds of meters of coastal highway suffered destruction; Zhongzhai to Tong'an submarine cables have also been washed out; Yingcuo to Aoguan red clay terrace, due to the long-term erosion of coastal erosion, the development of soil cliffs, and constantly triggered coastal collapse, landslides, soil and water intensity of the loss of a large amount of sand and mud into the sea, further exacerbating the problem of siltation in Xiamen harbor.

(2) Coastal erosion also often destroys seawalls, windbreaks and other shore protection projects, resulting in seawater back-up, engulfing a large area of good land, causing soil salinization and sand activities, deterioration of coastal geology and ecological environment, and a serious threat to the lives of residents along the coast, property safety. The east coast of Xiamen Island, Zengcuoan-HangZaiPu, 250m seawall is completely destroyed, and the shore protection project between Baishi Fortress has been seriously damaged, and Qingjiao 1,000m seawall has been similarly damaged, within the dike dozens of hectares of land, more than 1,000 residents and more than 10 factories, faced with seawater flooding, submerged in the danger.

(3) Although there is no obvious phenomenon of coastal erosion and retreat, but because the beach is constantly being reduced by erosion, thus triggering the deformation of the shore slope, displacement, destabilization, affecting the stability and safety of ports, wharves and other projects. With the deepening of the construction of the economic zone on the west coast of the Taiwan Straits, the construction of coastal engineering will continue to increase, and coastal erosion will become the main factor jeopardizing the construction of coastal engineering. According to the experience of developed countries, the most effective way to protect coastal erosion is to feed the beach and supplement it with engineering measures such as guide dike to promote siltation and outer breakwater cover. Of course, these measures still need to depend on the characteristics of the coastal geological environment, can also be used to beach artificial sand replenishment method.

4.2 Gulf siltation affects the sustainable development of port cities

Xiamen, Quanzhou, Zhangzhou are coastal port industrial and trade cities, especially Quanzhou has a long history, the rise and fall of the regional economy and the development of the coastal change is closely related.

(1) Quanzhou port in the Song and Yuan Dynasties (960-1368 AD), was a world-class port, the starting point of the "Maritime Silk Road", there are more than 15,000 large sea-going ships, the outer ports, including the ports after the mouth of the Luoyang River, the mouth of the Danyin River port of the port of Anping and the mouth of Quanzhou Bay otter cave island port, etc., navigating Japan, Korea, South Asia, West Asia, and East Africa, the port of the sea. It was also a major port in Japan, Korea, South Asia, West Asia, and East Africa. Yuan 29 years (1292 AD), Italian traveler Marco Polo, by the order of the Yuan Dynasty Emperor Kublai, escorted Princess Kokqing to marry Persia, it is from the port of Quanzhou set sail; in 1974 in the back of the port of the unearthed Song Dynasty wooden structure of the ocean-going ship (now preserved in the Quanzhou Ancient Ship Museum), is the port of Quanzhou witness to the glorious history of the port. However, in the 10th year of the Ming Dynasty (1474 AD), the Quanzhou City Hublot Department, which had been established for more than 380 years from the Northern Song Dynasty to the Ming Dynasty, was relocated to Fuzhou due to the silting up of the harbor, and Quanzhou was changed from the largest port city in China to a "Famous Historical and Cultural City". Many commentators have looked at the decline of Quanzhou harbor from the perspective of social factors, but the serious siltation of the harbor and the constant pushing out of the coastline are still hard facts. Zhangzhou Yuegang (Haicheng) emerged in the middle of the Ming Dynasty, mainly as a replacement for the declining port of Quanzhou. It used to be a bustling town with merchants and foreign ships; in the 15th year of the Yongli reign (1661 AD), the national hero Zheng Chenggong assembled his army here, organized an eastward expedition, and recaptured Taiwan in one fell swoop. But the good times did not last long, with the siltation of the bay, the channel silt, "five ports of commerce" Xiamen Port opened, Zhangzhou Yuegang also declined.

(2) port location should be stable shoreline, deep water in the harbor channel, less silt, sheltered from the wind, small waves, etc. as the principle. From the point of view of coastal change, Chongwu Peninsula shore section, Shishi Xiangzhi, Jinjiang Shenhu, the northeast coast of Kinmen and the size of the Strait of Kinmen, Zhangpu six Ao, under the Zhai, Dongshan Harbor, etc., the shoreline is relatively stable, with the conditions for the construction of the port. However, some sections of the shoreline seem to be able to build a harbor in the current situation; however, from the development trend of coastal change, it is inappropriate if effective measures are not taken to control it. For example, JiuLongJiangKou Xiamen Haicang - QianYu section, the north heart of the beach shoreline siltation rate of 121.0m / a, the east side of the island of Haimen siltation rate also up to 105.0m / a, accumulation rate of 21.0cm / a, if according to this rate of development after 30 ~ 40 years, the Yellow Sea elevation of the zero-meter line may be arrived at the QianYu. With the zero-meter line forward, the bay beach bottom gradually silt high, shallow water depth, very unfavorable to build a port.

4.3 Mudflat siltation brings new problems to aquaculture

It is usually believed that mudflat siltation is favorable to the development of aquaculture, but the rate of mudflat accumulation in this area is greater than the rate of sea level rise, so the area of coastal mudflat is still expanding, and the hydrodynamic conditions are also slowing down. The development of aquaculture needs to consider the development trend of the mudflat area in addition to the pollution of the mudflat geological environment.

(1) due to the estuary, the bay mudflats continue to silt up, every year there are new sediments covered in the old sediments on top of the benthic organisms and planktonic microorganisms, resulting in changes in the geological and ecological environment, and some organisms are difficult to continue to adapt to and reproduce the survival of the biodiversity of a serious threat. For example, Tong'an Bay in Xiamen, due to the construction of the river mouth, the Bay, Bizhou, Dongkeng large-scale reclamation and other factors, resulting in a large reduction in the flow rate of the falling tide, the rapid re-siltation of muddy sediments, the beach and the watercourse accumulation of the high rate of 2.0-5.0 cm / a, the silt layer as thick as 10-100 cm, making the original inhabitants of rare fish - Xiamen, Xiamen, the amphioxus (from invertebrate to vertebrate excess), due to the ecological environment of the typical specimens, the ecological environment is very difficult. (a typical specimen from invertebrate to vertebrate), which used to live in this area, was forced to migrate to the sandy waters of Huangcuo, Xiamen, due to the destruction of the ecological environment and the drastic decrease of its population, which was in danger of extinction.

(2) with the development of industrial and agricultural production, "three wastes" emissions are increasing day by day, the environmental pollution load increases, the river or the sea brings pollutants, often in the estuary, the top of the bay hydrodynamic conditions of the weak place of concentration, resulting in the mudflat siltation area of the lack of oxygen in the water or the content of hazardous elements dramatically increased; in this way, will change the native mudflats. This will change the geological and ecological environment of the native mudflats, making it difficult for aquatic organisms to continue to survive or produce a vicious cycle, and then unsuitable for aquaculture. This is the future of aquaculture industry have to face, need to study the new problems.

5 Conclusion

(1) The coastline of southern Fujian is 1,327.5km long, and the coast is divided into three major types: bedrock coast, sandy coast and silty coast. Among them, bedrock coasts are further divided into rocky coasts and weathered crust coasts; silty coasts are divided into harbor type and estuary type. Coastal mangrove forests have the functions of promoting siltation, preventing wind, fixing banks and purifying seawater; it is recommended that management and protection be strengthened, and artificial planting can be carried out in certain eroded bank sections to improve the ecological and geological environment of the coastal zone.

(2) Although the Holocene is a sea advance, there are many times of sea level fluctuation and shoreline change. Historical records and test data show that most of the coastal plains in this region were formed in the last thousand years. Jinjiang Shenhu Bay (1987), Zhangpu Qianhu Bay (1999), Dongshan Maluan Bay (2001), Shishi Shahu Bay (2005) and other places, one after another in the intertidal zone found the remains of primitive ancient forests, suggesting that the recent sea level is still rising trend, due to the various sections of the shoreline is located in different geological environments, the present coastline is still in the process of development and evolution.

(3) Coastal change is a comprehensive reflection of sea level and land rise and fall. In the whole region, the cumulative total of 445.0km of erosion coast, accounting for 33.52% of the total length of the coastline, mainly distributing strong weathering - dramatic weathering of bedrock coasts and sandy coasts; the cumulative total of 560.0km of silt coast, accounting for 42.18% of the total length of the coastline, mainly distributing the estuaries, harbors and bays of silt coasts; the cumulative total of 322.5km of stabilized (balanced) coasts, accounting for 24.29% of the total length of the coastline. Stabilized (balanced) coast accumulates 322.5km, accounting for 24.29% of the total length of coastline. Among them, the natural silt coast 360.0km, engineering to promote silt coast 200.0km, accounting for 35.71% of the silt coast; natural silt balance coast 72.5km, take engineering reinforcement measures, silt basic balance coast 250.0km.

(4) Coastal erosion tends to damage coastal highways, embankments, cables, and other infrastructures, threatening the ports, wharves and other shoreline projects. The coastal erosion often destroys coastal roads, embankments, cables and other infrastructure, threatens the stability and safety of ports, wharves and other shoreline projects, exacerbates siltation of ports and affects the economic development of coastal areas. Currently the most effective way to protect coastal erosion is to feed the beach, and supplemented by the guide dike to promote siltation and outer breakwater cover and other engineering measures, can also be used to beach artificial sand replenishment method.

(5) Xiamen, Quanzhou, Zhangzhou and other port cities, economic development and coastal change is closely related. Port site selection should be stable shoreline, harbor channel water depth, less silt, wind, wave, etc. as a principle. From the point of view of coastal change, Chongwu Peninsula shore section, Shishi Xiangzhi, Jinjiang Shenhu, the northeast coast of Kinmen and the size of the Kinmen Strait, Zhangpu Liu'ao, Xiazhai, Dongshan Harbor and other shoreline is relatively stable, with the conditions for the construction of ports.

(6) The rate of mudflat accumulation in this region is higher than the rate of sea level rise, so the coastal mudflat area is still expanding and the hydrodynamic conditions are slowing down. The development of aquaculture needs to consider not only the development trend of the mudflat area, but also the pollution of the mudflat geological environment.

References

[1] Xie Zaituan et al. Characteristics of marine encroachment and sea level change since the Late Pleistocene on the west coast of Taiwan Strait. Proceedings of the Symposium on Geology and Seismology of the Taiwan Strait and its Cross-Straits. Beijing: Ocean Press, 1991

[2] Chen Chenghui et al. A study of Holocene geochronology along the coast of southern Fujian. Taiwan Strait, 1982(2)

[3] Guangzhou Institute of Geography. Preliminary study of Late Quaternary sea level changes in southern Fujian.1987

[4] Zheng Xiaoyun. Sea level changes since the Late Pleistocene along the coast of southern Fujian. State Oceanic Administration, Xiamen, China, 1995

[5] Guo Yunmou, Li Qingnian. Evolution of Meizhou Bay, Fujian. Tropical Ocean, 1987, 6(6)

[6] Chen Feng. Formation of beach rocks in the Gulei Peninsula and sea level change along the coast of southern Fujian. Sea level change in China. Beijing: Ocean Press, 1986

[7] Chen Weiguang. 14C isotope dating data along the coast of South China. South China Earthquake, 1982, 4(4)

[8] Wang Shao-hong, Yang Jian-ming, Zeng Cong-sheng, et al. Sea level changes along the southeast coast of China over 50,000 years. Proceedings of Geology of Fujian Province. Fuzhou: Fujian Map Press, 1996

[9] Cai Lizhu. A preliminary study of the Quaternary microsomal paleontological assemblage and marine intrusion in borehole ZK3702, Xiamen, China. Fujian Geology, 1988, 7(3)

[10] Pan Guoxuan, Lin Dunyu et al. Report on the comprehensive survey on the geology and geomorphology of coastal zone of Fujian Province (on land). The Second Hydrogeological Engineering Geological Team of Fujian Province, 1986

The Environment Geology Problem of Coast Line Changes in South Fujian

Lin Jun

( Fujian Institute of Geological Survey, Fuzhou 350003)

Abstract: Under the global sea-level rising condition, coast erosion is the main natural disaster and gulf accumulation influence on sustainous development of Fujian. accumulation influence on sustainous development of the port city. Therefore coast erosion and gulf accumulation are considered as the major problem to be solved in improment of Therefore coast erosion and gulf accumulation are considered as the major problem to be solved in improment of coast geological environment. Based on the summary of characteristics of modem coast geography and coast line change since the Holocene , the present situation and the current situation of the coastline change are summarized. Holocene , the present situation and development tendency of coast line changes in South Fujian have been studied.

Key words: The coast changes; The coast erodes; The gulf accumulations are considered as the major problem to be solved in improment of coast geological environment. The coast erodes; The gulf accumulations; Environment geology; South Fujian coust areas