He Junmei, Lv Yaodong, Chen Huichuan, Liang Jiahai, Liang Xiangyang
(Guangdong Geological Survey Institute, Guangzhou 5 10080)
According to the geological survey data in recent years, it is considered that the eco-environmental geological survey of Pearl River Delta Economic Zone1:250,000 has made new progress and new understanding in urbanization development trend, characteristics of human activities, vulnerability of geological environment and environmental geological problems.
Vulnerability of geological environment; Environmental geological problems; Sustainable urbanization; Pan-urbanization; Pearl River Delta Economic Zone
The Pearl River Delta Economic Zone is located in the south-central part of Guangdong Province, adjacent to the South China Sea, Hong Kong and Macao. It is one of the three most developed and fastest growing economic units in the coastal areas of China, and it is also one of the most densely populated areas. There are only a handful of floating population in China, the integration of urban and rural areas is basically realized, and the process of rapid urbanization is rapid. A series of environmental geological problems have increasingly become the restrictive factors for the sustainable development of social economy in this area.
In recent years, under the unified arrangement of China Geological Survey, Guangdong Geological Survey Institute has organized and implemented the "1∶ 250,000 Eco-environmental Geological Survey of Pearl River Delta Economic Zone". Based on the results of this project, this paper summarizes the progress of environmental geological survey in recent years.
Understand 1 urbanization development trend and characteristics of human activities.
Urbanization trend is the most important physical feature of social and economic structure change, and it is the objective expression of the development of social form to the highest level. The level of urbanization is a significant symbol of the modernization of a country or region. Since the reform and opening up, the Pearl River Delta Economic Zone has experienced a historic socio-economic leap, rapid industrialization, rapid rise of urban agglomerations with Guangzhou and Shenzhen as the core, interactive development of the overall level of urbanization, and internationalization of rural "market towns", market towns "towns", county towns and small cities, and large and medium-sized cities. Since 1995, the vast rural areas in this area have reached the mature stage of urbanization, urban-rural integration has basically been realized, and the degree of urbanization and internationalization has been continuously improved. After more than 20 years of development, the Pearl River Delta Economic Zone has concentrated two megacities, Guangzhou and Shenzhen, nearly 10 large and medium-sized cities, more than 20 county-level central cities and more than 400 established towns, and the trend of pan-urbanization has gradually emerged (Figure 1). Although in terms of urban connotation, the mature rural urbanized areas in the region are not cities in the strict sense, and there is a huge difference between "permanent population" and "registered population", in terms of land landscape, the whole region has formed a very extensive metropolitan area. After the core area of the pan-metropolitan area matures, it has a tendency to expand to the periphery, and the extended non-Pearl River Delta areas are gradually integrated with the Pearl River Delta. With the influence and drive of the delta on the surrounding areas,
Under the trend of pan-urbanization, human activities in this area have obvious regional characteristics.
(1) The ways of human activities have increased. It has been expanded from agricultural activities, mining activities, land reclamation, dam construction and other aspects. arrive
Figure 1 Extraction of remote sensing images of urbanization pattern in Pearl River Delta Economic Zone
Note: The map is in the built-up area, and the pan-urbanization of Buddhism, Guangzhou, Dongguan and Shenzhen is clearly visible.
Urban development is closely related to economic construction, and human activities have now covered the utilization of various space resources on the earth's surface.
(2) The influence of human activities is multiple. Different types of human activities may cause the same type of eco-environmental geological problems. For example, regional reclamation projects may cause siltation in estuaries and ports, wetland changes, coastal mangrove ecosystem degradation and salt tide upwelling; Mine development causes surface water pollution, groundwater pollution, soil pollution and agricultural activities.
(3) The space for human activities has both aggregation and diffusion. In the overall planning of social development in this region, human activities are mainly concentrated in metropolitan areas, generally including Guangzhou (excluding Zengcheng and Conghua), Dongguan, Shenzhen (including Baoan District), Foshan (Chancheng District, Nanhai District and Shunde District), Zhongshan, Jiangmen (urban area and Xinhui District) and Zhuhai (including Doumen District). Human activities in plain areas mainly include urban construction activities, linear projects such as railways and highways, point projects such as landfills and agricultural activities; Development and utilization of environmental resources such as building materials, minerals and slopes. , mainly in hilly Taiwan Province area and hilly low mountainous area; The coastal zone is dominated by regional reclamation projects and the development and utilization of tidal flat resources.
(4) The intensity of human activities tends to increase. After the reform and opening up, especially since 1990, the intensity of human activities is increasing day by day. The data of three periods listed in table 1 and table 2 reflect the increasing trend of human activities. According to the results of remote sensing interpretation in the eastern part of the economic zone, urbanization is expanding on a large scale, and the urban construction area has increased from 65438+8.6% in 0990 to 14.8% in 2000, an increase of nearly 10%.
Double; The cultivated land area has been decreasing from 19% in 1990 to 13.6% in 2000 (Table 3). With the signing of the "9+2" Pan-Pearl River Delta Cooperation Framework Agreement, the pace of urban development in this region will be further accelerated. According to the statistics of urban planning area, by 20 10, the urban area of the whole region will exceed 1.0× 104 km2, and the non-agricultural construction land will reach 1.5× 104 km2 (accounting for more than one third of the total land area of the whole region). By then, more than 70% of the flat land in the whole region will become. It can be predicted that in the next few years or even decades, human engineering activities will be unprecedented.
Table 3 1990 and 2000 NDVI index partition value comparison table
1990 (%) and the percentage of NDVI value in the total area in 2000 (%).
-1~-0.5 Water body (rivers, lakes and seas) 24.3 24.438+0
-0.5~0 Urban architecture 8.6 14.8
0~0.5 Crops, Cultivated Land and Aquaculture 19.4 13.6
Bamboo forest 0.5~0.75, shrub and grassland (vegetation) 25.4 ~ 24.9.
0.75~ 1 forest (vegetation) 22.3 22.6
(5) Human activities are becoming more and more orderly. The disorder of human activities will be alleviated. The so-called disorder refers to the situation that human activities are blind, do not consider the consequences, and lack guidance and supervision, which easily leads to the variation of eco-geological environment and causes eco-environmental geological problems. With the improvement of education level, the strengthening of people's awareness of environmental protection, the improvement of legal system and supervision system and the development of related technologies, human activities will be standardized, so disorderly activities will be curbed to a certain extent. Nevertheless, large-scale planned human activities still need to fully consider the possible consequences.
2 vulnerability of geological environment: looking at environmental geological problems from a geological point of view
Human activities are the external cause of the formation and development of environmental geological problems, and the fragility of geological environment is its internal cause. Understanding the fragility of geological environment is undoubtedly helpful to the study of environmental geological problems. The vulnerability of the geological environment in the Pearl River Delta Economic Zone is mainly reflected in the following aspects.
2. 1 The residual soil layer in bedrock area is relatively developed.
The area of bedrock in this area accounts for about 60% of the total land area, and the distribution area of magmatic rocks dominated by intrusive rocks (granitoids) accounts for about one third. Due to the strong weathering of rocks, residual soil layer is developed in bedrock area. Granite distribution area is mainly due to the high content of unstable minerals such as feldspar and mica (generally about 70%) and the thickness of residual soil layer (> > 20 m), which is prone to soil erosion. Except for the weathered residual soil in the middle and high mountains and coastal islands, the hilly terrace area is generally more than 5 m; The residual soil in the distribution areas of metamorphic rocks and volcanic eruption rocks is mostly cohesive soil mixed with breccia debris, and its thickness is generally less than 3 m, so debris flows are prone to occur in the distribution areas.
2.2 Quaternary loose sedimentary areas are generally developed in soft soil.
Quaternary loose sediments are widely distributed in the Pearl River Delta Economic Zone, accounting for about 2/5 of the land area. Genetic types include alluvial, diluvial, alluvial, marine and alluvial. Alluvial, diluvial and alluvial sediments are mainly distributed in valleys and river terraces at the edge of the delta, and their thickness is generally less than 10 m, and they often have a dual structure. The upper part is medium-fine sand or silty clay, and the lower part is coarse gravel with carbonized wood blocks. Peat soil formed by alluvial of the first terrace is 7580 170A. Alluvial deposits and marine deposits are widely distributed in the delta plain and coastal areas, which are mainly the products of the interaction between bay deposits and coastal river alluvial deposits in the middle and late Holocene transgression period, with an average thickness of 25. 1 m and a maximum thickness of 63.6 m. The upstream is mainly grayish yellow or grayish brown silty clay and muddy clay, and the downstream is mostly dark gray silty silt and silt.
The distribution area of soft soil layer is nearly 8 000 km2, accounting for about one fifth of the total land area in the whole region. Among them, the delta plain with the densest cities and towns is the most widely distributed area, and the distribution area of soft soil accounts for 82.25% of the total distribution area of soft soil in the economic zone. From the tip of the Pearl River Delta to the estuary, the thickness of soft soil increases, the number of layers increases, and the degree of consolidation becomes worse. The cause of formation changes from floodplain to marine facies, and the lithology changes from silt facies to silt. According to borehole data, 14C dating and pollen analysis results, the soft soil in the delta can be roughly divided into three layers in the vertical direction, corresponding to three major transgressions in the delta area from late Pleistocene to Holocene respectively. The younger the sedimentary age, the greater the thickness of soft soil, and the greater its water content, liquid limit, liquid index and porosity ratio, while the older the sedimentary age, the greater its mechanical strength, which means the smaller its compressibility and porosity. Under the influence of natural forces or human activities, the soft soil layer is prone to land subsidence, which is harmful to the ground and engineering buildings.
In addition, the distribution area of easily liquefied sandy soil in the river network area of Dongjiang Delta and Huizhou section is 2 13 km2, the buried depth is generally 1.5 ~ 12.8m, the thickness is 1.5 ~ 10.5m, and the SPT count is 2.3 ~ 7. Loose and saturated silty sand, fine sand and silty soil are liable to liquefy once they are subjected to dynamic loads (earthquake, piling, blasting and mechanical vibration), causing damage to the ground and engineering buildings.
Table 4 Geological characteristics and physical and mechanical properties of soft soil in Pearl River Delta
Main characteristics of silt layer deposition period, main physical and mechanical properties of roof depth and thickness (average value)
Maximum value of general average w0 wL IL e0 a 1-2 Es C
m % % - - MPa- 1 MPa kPa
The first layer contains 0.0 ~ 5.01.5 ~ 21.9 9.5 42.7 60.2 45.71.891.661.44 2.45 6.90.
The second layer contains Holocene oyster shells, often mixed with fine silty sand 2.6 ~ 20.81.5 ~1.06.37.550.640.1.641.340.990.
At the end of the late Pleistocene, the third layer contained marine shell debris, and flooded the plain saprophytes 5.3 ~ 24.00.6 ` 7.9 3.7 20.4 42.3 38.61.261.kloc-0/80.755.01.
2.3 neotectonic movement is active
Neotectonic movement has been active since the late Cretaceous-Tertiary, mainly inherited activities. According to the geological records of Guangdong Province, there are NE-NNE deep fault zone, Zijin-Boluo fault zone, Dongjiang fault zone, Enping-Xinfeng deep fault zone, Wuchuan-Sihui deep fault zone, EW-Gaoyao-Huilai deep fault zone, NW-trending Xijiang fault zone and Zhuhai-Xindu fault zone in this area [4]. Gaoyao fault, Enping-Cangcheng fault, Jinji-he cheng fault, Guangzhou-Gulao fault, Guangcong fault, Guangsan fault, Shenzhen fault, Pinghai fault, Tanghu fault, Chishi-Shatian fault, Xijiang fault, Shajiao fault and Yamen fault are still active. For example, according to the monitoring data of Seismological Bureau, the activity of Guangcong fault in 1973~ 1979 is 26.5 mm, with an average annual activity rate of 4.4 mm; ; The maximum variation of the height difference on both sides of Guangsan Fault (a part of Guangsan Fault) in Guangzhou is 2.38 mm in March, 1997, 1 1 ~ 1. The monitoring results of Shenzhen Geological Bureau in recent five years show that: ① Shenzhen fault is in a state of slow stress creep, and the trend creep rate is 0.17 ~ 0.35 mm/a. ..
2.4 karst development of concealed carbonate rocks
The distribution area of carbonate rocks in Zhaoqing City, Guanghuapingdi, Enping-Kaiping, Longgang District, Huiyang Danshui Town, Aipi Town and Paitan in Zengcheng City is 1474 km2, but most of them are covered by Quaternary loose sediments. Carbonate rocks are mainly produced in Ordovician Luohong-Luodong Formation, Devonian Tianziling Formation, Chunwan Formation-Tianziling Formation, Carboniferous Lianxian Formation, Shihezi Formation (Cs), Tanshui-Zimenqiao Formation, Zimenqiao-Dabu Formation, Dabu Formation, Hutian Formation (CH) and Permian Qixia Formation, with Hutian Formation and Shihezi Formation as the main ones. Taking Guanghua Basin as an example, the thickness of Quaternary loose sediments is generally 10~25 m, the surface layer is mainly cohesive soil (locally silt), and the bottom is often in contact with limestone, and the karst strong development zone is located at the elevation of -20~-80 m underground. The hydrogeological conditions and geotechnical structure in the concealed karst area are very conducive to the formation of ground collapse.
2.5 Vulnerability of Soft Rock Engineering
The Cretaceous-Tertiary red beds distributed in Gaoyao-Sanshui-Guangzhou-Dongguan, Enping-Kaiping, Huizhou, Boluoyangcun, Huiyang and Huidong-Baipenzhu, and the Jurassic-Carboniferous coal-bearing strata distributed in the delta margin are often sandwiched with mudstone, sandy mudstone, shale, carbonaceous shale, coal, gypsum, salt rock and other soft rocks with relatively low mechanical strength. The exposed surface of this rock is easy to weather, often expands and softens when it meets water. The softening coefficient is 0.26~0.5, and the saturated compressive strength is 0. 14~ 1.2 MPa. Among them, gypsum and salt rock are easy to produce dissolved holes or ditches under the long-term dissolution of groundwater. If these rocks are selected as the bearing stratum of foundation, buildings are prone to slip and uneven deformation of engineering foundation, and the mountains and slopes of engineering construction site will produce geological disasters such as landslides along the weak surface, so this kind of rock stratum is unfavorable to engineering construction.
3 environmental geological problems: genetic classification and socio-economic impact
The process of urbanization is a process of population gathering, industrial gathering, economic growth, social production and lifestyle change, as well as a process of large-scale resource consumption, spatial gathering, destruction of natural landscape pattern and formation of urban landscape pattern. On the one hand, socio-economic development and urbanization are restricted by fragile factors of geological environment, on the other hand, human economic engineering activities inevitably lead to environmental geological problems. The environmental geological problems in the Pearl River Delta Economic Zone have different degrees of influence on the sustainable development of social economy, mainly including soft foundation settlement, urban flood, water and soil pollution, water quality shortage, resource shortage, structural stability, hidden karst collapse, natural soil erosion, man-made soil erosion, collapse, landslide and debris flow, etc. According to the genetic types, it can be divided into three types: primary type, secondary type and combined primary and secondary type.
3. 1 Main environmental geological problems
Structural stability 3. 1. 1
Earthquakes with small magnitude, high frequency and dense clusters reflect the structural stability of the Pearl River Delta Economic Zone. Earthquakes in this area mainly occur in the active fault zone and its intersection, and earthquakes are often distributed in bands and groups, while earthquakes with larger magnitude are mainly distributed along the northeast active fault zone. Historically, earthquakes mainly occurred in Guangzhou, Shunde, Zhongshan, Xinhui, Taishan, Zhaoqing, Sihui and other places west of the Pearl River Estuary, while modern earthquakes after 1970 were mostly distributed in the coastal areas south of Enping-Taishan-Doumen-Shenzhen. According to the historical data of earthquakes, there were 2 15 earthquakes of magnitude 3 or above in this area, including 4.75 destructive earthquakes 13 times. Since 1970 was recorded by instruments, there have been 2 earthquakes of magnitude 2.0 or above in * * area, with an annual average frequency of 7 times /a, including 59 earthquakes of magnitude 3 or above and 4 earthquakes of magnitude 4 or above (none of which exceeded magnitude 5).
3. 1.2 Resource water shortage
However, the problem of water shortage in coastal areas and islands such as Huidong Pinghai-Huiyang Xia Yong-Daya Bay-Shenzhen-the east coast of the Pearl River Estuary is outstanding. At present, the urban water supply mainly depends on the remote dispatching of Dongjiang water source, and the local area lacks surface water resources and underground water resources that can be used as urban centralized water supply. Once the quantity and quality of water resources change due to the drought year or the increase of upstream pollution, the water supply problem will become more severe. Shenzhen has become one of the seven cities with serious water shortage in China.
3. 1.3 Debris Flow
There have been 36 small debris flows at 1 1 in this area, such as Jurassic volcanic eruption rocks (Jkn, Jkb, Jr) with steep mountains and slopes in Huidong. Is the most likely to happen. Because volcanic eruption rocks are distributed in low mountains and hills, the terrain is steep (generally, the slope above the mountainside is >: 30), the rocks are affected by structure and weathering, the residual soil thickness is not large, and the contact interface with weathered rocks is obvious. Residual soil is mostly gravel mixed cohesive soil with loose structure. In case of rainy season, clay minerals in residual soil swell and soften with water, and weathered rock and soil with good catchment conditions and steep slope pour down along the ravine, forming debris flow. However, due to the thin weathered rock and soil and small catchment area, mudslides will occur. However, it has done great harm to nearby residents and buildings near the mountain. Debris flow not only destroys forest land, affects landscape, but also directly threatens people's lives and property. It has become the main factor of ground instability in this area and the major hidden danger of regional ecological environment construction. 1997, a two-story building at the foot of the mountain was washed away by a mudslide in Wulian Village, Huadu District, Guangzhou, and 10 residents were killed.
3. 1.4 Natural soil erosion
Natural soil erosion is mostly distributed in hills with sparse vegetation and Taiwan Province area, and consists of granite residual soil layer. Huidong County, Huadu District, Conghua City, Taishan City and Jiangmen City have the most extensive granite distribution areas (including islands) and the greatest negative impact. The natural soil erosion area in this area is 630 km2, accounting for 43% of the total soil erosion area.
3.2 secondary environmental geological problems
3.2. 1 Water and soil pollution
There are more than 6 000 small and scattered secondary polluting enterprises in the towns and villages of the Pearl River Delta, and there is a general lack of effective sewage treatment facilities. A large amount of sewage is discharged into the river. At present, the annual sewage discharge exceeds 20× 108 t, and industrial solid waste 180× 104 t and domestic garbage 300× 100t are also generated every year. The river sections flowing through the urban areas of various cities are polluted to varying degrees, and the boundary rivers of various cities are seriously polluted. The pollution of water bodies and sediments in the Pearl River water network and estuaries, especially the pollution of toxic and harmful heavy metals, organochlorine pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls and other organic substances, has sounded the alarm for the safety of the ecological environment. The results of geological survey made by Guangdong Geological Survey Institute show that the soil environmental quality in the Pearl River Delta is not optimistic, and there have been large-scale regional pollution dominated by toxic heavy metal elements such as cadmium, mercury, arsenic and copper, as well as large-scale pollution of harmful elements such as fluorine and sulfur. The pollution of toxic and harmful elements in soil and its influence are worrying. Zhang et al.' s research confirmed the existence of organochlorine pesticides and polycyclic aromatic hydrocarbons pollution in soil. The present situation of non-organic pollution of groundwater is discussed in the evaluation report of groundwater resources completed by Guangdong Geological Environment Monitoring Station. Academician Fu Jiamo wrote an article summarizing the persistent organic pollutants in the environment and the environmental pollution problems caused by them. A paper published by the Geological Department of China Academy of Sciences in Progress of Earth Science published a lot of data about water and soil pollution in the Pearl River Delta.
The pilot project of groundwater pollution investigation and evaluation in the Pearl River Delta launched in 2005 shows that there are 35 kinds of organic pollutants in this area, including 9 kinds of halogenated hydrocarbons, 8 kinds of monocyclic aromatic hydrocarbons, 3 kinds of polycyclic aromatic hydrocarbons, 1 1 organochlorine pesticides, 1 ketones and 3 kinds of phthalate esters.
A large number of facts show that water resources, land resources and biological resources are qualitatively changed by water and soil pollution, which directly threatens the living environment, harms human health and affects the sustainable development of regional social economy.
Shortage of water resources
Under the background of soil and water pollution, although the per capita water resources in this area are 14580m3, which is much higher than the national average of 2,500m3, the surface water resources that meet the drinking water quality standards are limited, and the groundwater is mostly salt water with salinity >: 1, which leads to Guangzhou (including Panyu and Nansha Development Zone), Dongguan and Foshan (including Shunde District) around the Pearl River Estuary metropolitan area.
3.2.3 Man-made soil erosion
The man-made erosion area is 840,000 m2, accounting for 57% of the total soil erosion area. Man-made erosion is mostly distributed near cities or densely populated towns, mainly in the erosion types of human construction and development sites, mostly in undeveloped land, construction site slopes (including traffic engineering and construction sites), steep slope land reclamation, mining and soil borrowing areas, among which Shenzhen, Dongguan and Zhongshan, which have strong human activities and developed economy, have the largest distribution areas. In addition, soil erosion caused by mining operations is also very serious in some areas.
With the occurrence of man-made soil erosion, rivers, ponds and reservoirs are shallowly silted, riverbeds are raised, and floods occur frequently, resulting in crop yield reduction and crop failure. For example, the 5 km river course of the Shangde kaolin mine field in Hetai is seriously silted, and a large area of fertile land is submerged, including the river course of Kengkou Village (about 6 m thick), where more than 20 houses were buried 10, and more than 20 houses were washed away, and the whole village was forced to move10 m; ; The kaolin mine in Shizui Village, Aotou Town, Conghua caused siltation in the downstream river (about 3~5 m thick), and the farmland on both sides of the river was buried for several kilometers.
3.3 the combination of primary and secondary environmental geological problems
3.3. 1 soft foundation settlement
In the plain area, the soft soil near the Pearl River Estuary has a large thickness and a short formation time, which is the key section of soft foundation settlement. Soft soil foundation is concentrated in the section with soft soil thickness greater than 20 m, and the representative areas are the south of Panyu District in Guangzhou, the northeast of Zhongshan City and the southwest of Zhuhai City. Guangzhou Nansha Economic and Technological Development Zone, Zhuhai West Zone, Gujinzhou Development Zone of Xinhui District of Jiangmen City and Hengmen Town of Minzhong Town all have obvious regional soft foundation settlement. There are also obvious settlement phenomena in soft foundation sections such as Zhuhai Avenue, Xintai Expressway, Guangfo Expressway, Guangzhou-Zhuhai Expressway and domestic expressway in Zhongshan City, Zhuhai City and Panyu District of Guangzhou City. According to the comprehensive analysis of the survey data, the zoning of prone degree of settlement disaster of soft soil foundation is obtained.
According to the survey data, the accumulated settlement in this area up to 2003 is generally 0.3 ~1.7 m. The comparison between the third-class leveling of Zhuhai Avenue pavement in 2003 and 1994 shows that the average annual settlement of Zhuhai Avenue 10 is 0.37 m, and the maximum settlement is 0.73 m.). The cumulative ground subsidence of the golf course in Jinwan District of Zhuhai City is 2.97 meters, which is the largest cumulative subsidence found so far. In the section with soft soil thickness greater than 30 m, the average settlement rate is mostly between 0.1~ 0.3 m/a.
Most of the engineering buildings built in the newly deposited soft soil distribution area are affected by the settlement of soft foundation to varying degrees. Some low-rise buildings built directly on soft soil crust often sink and crack with the ground as a whole, while middle-high-rise buildings with bedrock as the bearing layer often collapse and hang their feet; On the highway passing through soft soil area, there will be some phenomena such as road surface fluctuation, subgrade displacement, uneven settlement of road-bridge junction and road surface cracking. The settlement of soft foundation seriously affects the normal use of infrastructure such as industrial and civil construction projects, dike water conservancy projects, underground water supply and power supply networks, or makes the road surface uneven and unable to operate normally. This not only caused economic losses of hundreds of millions of yuan in the southern coast, but also led to the neglect of some commercial and residential buildings, which seriously affected the investment environment.
3.3.2 Urban floods caused by siltation of ports, rivers and inlets and coastal changes.
Before the Tang Dynasty, the average speed of the coastline advancing toward the sea in this area was less than10.2m/year, during the Tang and Song Dynasties, it was about15m/year, and after the Song and Ming Dynasties, it was about 20m/year ... Large-scale human economic engineering activities caused abnormal changes in the coastline 120 years, especially from Wanqingsha to Hengmen and Denglongsha. From 1883 to the early 1980s, the average advancing speed of Wanqingsha and Denglangsha into the sea reached 63.3m/year and121.7m/year respectively. During the period of "grain as the key link" in the 1960s and 1970s and the early days of reform and opening up in the 1980s and 1990s, the coastline of this area, especially the Pearl River Estuary, rapidly pushed to the South China Sea (Table 5), and the area pushed to the sea in the whole area increased by 6 19.23 km2, of which the Pearl River Estuary increased by 552.95km2 The urban construction area of coastal beaches expanded rapidly from14.625 km2 in 1986. At present, the reclamation outside Hengmen in Zhongshan City has reached 23 surges, and the reclamation in Panyu District has reached 2 1 surge. The reclamation of Baiteng Lake in Doumen District of Zhuhai City led to the closure of Niwan Gate, and the islands of Sanzao Island and Qinheng Island in Zhuhai were connected with the inland.
Table 5 The rate of coastline advancing to the sea from Humen to Hengmen and Denglongsha to Pingsha Farm (unit: m/year)
Matters needing attention in lot1973 ~19901990 ~ 2002.
Wanqingsha 5 14.7 29 1.6 advances in the southeast.
The propulsion direction of Longxue Island 303.9 583.3 is southeast.
The heading direction of Hengmen Island at 225.5 527.8 is southeast.
The propulsion direction of Denglongsha 250.0 770.8 is southeast.
Pingsha Farm 58.8 ~102.9 270.8 ~ 416.7 pushed towards the southwest coast, which led to land expansion and water area shrinkage, spatial pattern change of siltation, ecological destruction of wetlands, deterioration of ecological environment, increased risk of flood disaster in the hinterland of the delta, and intensified water shortage situation, which had a negative impact on urbanization and economic development. The influence of embankment water and reclamation is increasing. Every year, about 20% of the sediment in the upper reaches of the Pearl River is deposited in the rivers in the network river area, which makes the rivers shallower. The remaining 80% reaches the Pearl River Estuary and the outer coast, which makes the siltation near the estuary about 7 ~ 17 cm/a ... Guangzhou Port, Huangpu Port and other port channels appear siltation to varying degrees. The siltation in Guangzhou Port is the most serious, with the annual maximum siltation thickness of 125.0 m, generally 0.5 m, which makes the port dredging 65,438+200,000 m3/a. In the future 150 ~ 200 years, the Lingdingyang Ocean may be silted up, and the water level in Guangzhou will be 2. According to the estimation of National Ocean Information Center, the sea level will rise by 30cm, and the highest tidal level will flood the coastal areas and islands in this area 1, 654,38+0,54km2. Abnormal coastal changes closely related to human activities have caused shallow siltation in the Pearl River bed, rising water level in the upper reaches, stagnant river sewage caused by upstream tides, and aggravated water and soil pollution. If the influence of sea level rise is superimposed, the existence and aggravation of these problems will increasingly become the limiting factors of urban development.
3.3.3 Concealed karst collapse
The development of hidden karst in Longgang-Kengzi-Pingdi area of Shenzhen, Guanghuapen land, Paitan of Zengcheng, Zhaoqing City and Taishan of Jiangmen City has become an important geological environment constraint for urban expansion, and ground collapse occurs from time to time driven by human activities such as groundwater exploitation and drainage. In recent years, 15 hidden karst collapse occurred in Guanghua basin, accompanied by environmental geological problems such as cracks in surrounding houses and dry wells. The Lantian quarry in Chini Town, Huadu District was drained by a large amount of water, and a fish pond in Zhongdong Village was drained. More than 200 houses were cracked to varying degrees, and some houses collapsed to form a big pit, threatening 600 people. According to incomplete statistics, the economic loss caused by karst collapse in Guanghuapen land exceeds 10 million yuan. Since 1986, there have been 25 hidden karst collapses in Longgang-Kengzi-Pingdi area of Shenzhen.
3.3.4 Collapse and landslide
Due to the fragile geological environment, heavy and concentrated rainfall and the superposition of human activities, the residual hills in mountainous areas, plains or plain areas often have sudden geological disasters such as collapse and landslide in rainy season, which are characterized by high frequency, small scale and great harm. The steep slopes in the northeast of Huidong, Huadubei, Conghua, Shenzhen and other places often collapse, bedding sliding often occurs along the flaky structural plane of metamorphic rocks and the soft and hard layers of clastic rocks, while massive rocks often occur at the contact surface between residual soil and parent rocks. A typical example is the landslide near Meilin border checkpoint in Shenzhen Special Economic Zone on September 18, 2002. Due to hydrodynamic action, the banks of rivers, oceans, lakes and reservoirs collapse-landslide. A typical example is the collapse of Xijiang River in Gaoyao, Zhaoqing on June 65438+1October 365438+1October 0, 2003. Man-made slopes, including site slopes developed and built along mountains and road cutting slopes, are prone to collapse and landslide on a small scale but with serious disasters. The site slope collapse occurred in Shunxing Industrial Zone, Liaocun Village, Shiyan Town, Baoan District, Shenzhen on May 5, 2003 is the most typical.
4 Conclusion theory
The Pearl River Delta Economic Zone is located in the transition zone and sensitive zone of geological environment, and the geological environment is fragile. Under the trend of pan-urbanization, the impact of human economic engineering activities on the geological environment will increase, and environmental geological problems will increasingly become a restrictive factor for the sustainable development of social economy in this area.
In recent years, some new progress has been made in the environmental geological survey of the Pearl River Delta Economic Zone, and some new understandings have been gained in the development trend of urbanization, the characteristics of human activities, the vulnerability of geological environment, the classification of environmental geological problems and their influence on the sustainable development of social economy.
References:
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