(1. Jinan University, Jinan 250002; 2. Shandong Bureau of Geology and Mineral Resources, Jinan 250013; 3. Shandong Institute of Geology and Mineral Resources, Jinan 2500 14)
About the author: Xing Liting (1966-), male, researcher, mainly engaged in hydrogeological and environmental geological exploration.
According to the field investigation results, the influence of natural and human factors on karst groundwater environment in Jinan spring area is deeply discussed, and some water environment protection countermeasures such as optimizing mining layout and recharging water are put forward.
Keywords: Jinan spring area; Water environment; Evolution; protect
Jinan spring area is a typical representative of karst water system in northern China. Its geological conditions are extremely complex and strongly influenced by natural factors and human activities. In recent decades, the eco-geological environment of the spring area has changed significantly. Studying the evolution characteristics of groundwater environment in this area is of great significance to the sustainable utilization of groundwater resources and the protection of spring water.
1 Hydrogeological characteristics of spring area
1. 1 spring boundary
Jinan spring area is located in the northern wing of Taishan dome, which is generally a monoclinal structure with Paleozoic strata as the main body and tilted to the north. The exposed strata are Archean Yutaishan Group, Paleozoic Cambrian, Ordovician, Carboniferous, Permian and Cenozoic Quaternary, and intermediate-basic intrusive rocks are distributed in the northern part of the spring area. Fault structures are developed in this area, mainly including Qianfoshan fault, Mashan fault, Wu Dong fault and Chaomidian fault.
The eastern boundary of the spring area is Wu Dong fault, the western boundary is Mashan fault (the permeable section is north of Xiguan in Changqing), the southern boundary is the surface watershed, and the northern boundary is bounded by Jinan magmatic rocks and Carboniferous and Permian coal measures strata, with an area of 1486km2.
1.2 hydrodynamic conditions of karst groundwater
Cambrian-Ordovician limestone is widely distributed in the southern mountainous area of Jinan, with well-developed surface and underground karst. The dense distribution of karst caves, gullies, troughs and dissolution cracks on the limestone surface creates extremely favorable conditions for groundwater to receive direct infiltration recharge from atmospheric precipitation and leakage recharge from surface water. According to drilling data and tracer tests, carbonate caves, dissolved holes, dissolved joints and dissolved pipes are well developed, which provides a huge space for the storage and migration of karst groundwater. Therefore, Jinan karst groundwater has good recharge conditions and huge storage space.
According to the dynamic observation of groundwater, karst water level and spring flow are closely related to precipitation. The direct infiltration of atmospheric precipitation is the main recharge source of karst water system, followed by surface water seepage recharge. The main leakage rivers are Yufu River and Beishahe River.
The general flow direction of karst water is from south to north, which is blocked by Yanshanian magmatic rocks and Carboniferous and Permian strata in the north, and a karst water-rich area is formed in its contact zone. The water inflow of a single well is generally above 5000m3/d, and karst water is mainly discharged by spring water under natural conditions. At present, artificial mining is the most important way to discharge karst water system in spring area.
2. Development and utilization of karst groundwater resources
Ordovician fractured karst aquifer has a long history as the main water intake destination layer for industrial and agricultural water and urban domestic water in Jinan. Baotuquan Water Plant was built in the urban area as early as 1936, and was officially supplied with water. The water supply is 1.28× 104m3/d, which is increased from 1956 to 3.6×104m3/d. With the development of economy and the increase of population, the water consumption has been increasing to 204m3/d, with jiefang bridge, Plymen, Yinlakes and marshes and Department Store waterworks in the urban area, Lashan, Emeishan and dayangzhuang waterworks in the western suburbs, Huaneng Road and Dongyuan Waterworks in the eastern suburbs, and Yangtouyu and Wenhua Road waterworks in the south.
1990 ~ 2002, the average annual output of Quanyu Water Supply Company was 35.52× 104m3/d, among which the average output of Emei Mountain, dayangzhuang and the western suburb of Lashan was 21.9/kloc-0 /× 104 m3/d.
Industrial self-provided wells are mainly distributed in the periphery of urban areas, with a large number and relatively scattered. From 1990 to 2002, the average annual output of industrial self-provided wells was13.15×104m3/d.
3 the evolution of hydrogeological conditions and the negative impact of groundwater environment
Natural factors and human activities have intensified the evolution of Jinan's eco-geological environment and caused many eco-environmental geological problems.
3. 1 Changes in hydrogeological conditions caused by human activities
3. 1. 1 Artificial mining changes the groundwater flow field and attacks the spring flow.
In the early 1960s, the groundwater exploitation in Jinan was insufficient 10× 104m3/d, and since 1980s, the centralized exploitation in urban areas, western suburbs and eastern suburbs has reached (50 ~ 55 )× 104m3/d ... A large amount of karst water has changed the natural flow field of groundwater, and a large amount of groundwater has been exploited. In September of 2000 1 year, the urban water plants were closed one after another, but a large number of industrial self-provided wells were exploited, and the two drip buckets of Qixianzhuang and Economic College still seized the spring water supply (Figure1).
3. 1.2 The replenishment quantity in the indirect replenishment area is reduced.
The indirect recharge area of Jinan spring area covers an area of 990km2, mainly distributed in the vast mountainous areas in the south, including Mashan, Wande, Goer, Zhang Xia, Gushan, Zhonggong, Liubu and Xiying. The strata are limestone, clastic rock and metamorphic rock of Taishan Group of Middle and Lower Cambrian. Due to the poor infiltration conditions, criss-crossing rivers and valleys, and the development of surface runoff, most of the groundwater is replenished locally, collected in the valleys, and transported and discharged in short distances. Therefore, most rivers originate here. Before 1970s, the upstream surface streams gathered in Yufu River and Beida Shahe River, and then flowed downstream, respectively, leaking to recharge the groundwater in the spring area in Zhujiazhuang-Pancun and Gushan barrage-Pipashan sections. The indirect recharge area collects surface runoff and underground overflow and enters the direct recharge area through the river channel. For example, 1963, Wohushan Reservoir discharges into the Yellow River through spillway1.0186×108m3, and partially seeps into groundwater. Before the construction of Wohushan Reservoir, the Yufu River basically flowed all the year round. According to 1962 observation, on April 13, the water level of Zhouwangzhuang reach in the lower reaches of Yufu River was 29.4m m.
Figure 1 isobar of karst water near urban area
1- failure; 2- Igneous rock boundary; 3— Isohydrograph (m); 4- Groundwater flow direction
In 1960s and 1970s, many reservoirs were built in rivers such as Beishahe River, Jinyinchuan River, Daiyuhe River and Jinxiu River to intercept the upstream surface runoff. Especially in the late 1980s, after the Wohushan and Jinxiu River reservoirs supplied water to the urban area, the surface water supply in the indirect recharge area gradually decreased. For example, from 1999 to June 2003, the catchment area of 554km2 in the upper reaches of Wohushan Reservoir was not discharged to Yufu River except for the recharge test. Since the Wohushan Reservoir and Jinxiu Chuan Reservoir supplied water to the urban area, the irrigation amount of the two reservoirs to Dangjiazhuang, Xinglong and watershed direct subsidy areas has gradually decreased.
3. 1.3 Urban expansion reduces the recharge area of karst water infiltration.
Urban construction increases the area of urban built-up area, which leads to the gradual decrease of the area of karst water direct recharge area. According to multi-temporal dynamic remote sensing interpretation, 1954 Jinan urban area is only 28.8km2, and the direct compensation area is less than 2km2. With the continuous expansion of the city scale, the direct recharge area of the urban area has gradually expanded to the east, southeast, south and southwest, and in recent years it has expanded by 175.6km2 compared with the 1950s. Since 1980s, urbanization has been expanding southward, and the built-up area of direct recharge area has increased year by year (Figure 2), thus reducing the recharge of groundwater. Such as Taipingzhuang, Yangtouyu, Baliwa, Liulishan, Jinjiling, Mashanpo, Xinglong and other southern mountainous areas, the ground solidified after development, and the atmospheric precipitation directly entered the flood control ditch. However, the flood control ditch is seriously silted and the terrain slope is large, which can not form effective infiltration, and many areas become permanent non-leakage areas. In 2000, the built-up area in the direct replenishment area increased from 1.954 square kilometers to 5 1.3 square kilometers. Based on the average annual precipitation of 648mm, due to the influence of urban expansion, the groundwater recharge decreased by 3.8×1.04m3/d.
3. 1.4 Impact of indiscriminate mining and excavation on ecological environment
According to incomplete statistics, there are more than 200 quarries in the southern mountainous area of Jinan. Quarrying and excavation cause the destruction of landscape and vegetation, resulting in a lot of soil erosion. According to the survey, a large number of quarries were built after the 1980s. Due to the thin soil and the scarcity of trees and vegetation in limestone mountainous areas, the vegetation coverage rate in the direct recharge area is further reduced due to rock mining. In the direct recharge area, quarrying and brick burning cause serious soil erosion, which reduces the water storage capacity and groundwater recharge capacity.
Figure 2 Urban expansion and evolution map
1-1954 urban area; 2- 1970 urban expansion scope; 3- 198 1 year urban expansion scope; 4-2000 urban expansion scope
3.2 the negative impact of groundwater environment
3.2. 1 The groundwater level drops and the spring water is cut off.
In the early 1960s, the amount of groundwater exploitation was relatively small, with an average groundwater level of 3 1.54 ~ 30.72m and a spring flow of (35.52 ~ 33.58) ×104m3/d; In the mid-1970s, the groundwater level dropped to 28. 15m, and the spring discharge dropped to about15.22×104m3/d; From the end of 1970s to the beginning of 1980s, the average groundwater level dropped from 28. 15m to 26.68m, and the spring discharge dropped to about10.48×104m3/d; In 1990s, the spring water cut-off time was prolonged, and the spring water cut-off lasted from 1999 to 200 1 and reached 932d (Figure 3).
3.2.2 Formation of the Falling Funnel of Groundwater Overexploitation
Long-term centralized exploitation of groundwater has formed a number of landing funnels in the eastern suburb industrial zone, Qixianzhuang and Economic College, robbing the supply of spring water.
3.2.3 Daming Lake and Xiaoqing River pollution
Due to the drop of groundwater level, the spring water is cut off, and the water in Daming Lake and Xiaoqing River is not fully replenished, which leads to serious eutrophication.
3.2.4 Groundwater quality decline
In 1950s, Jinan was in a natural flow field because of its underdeveloped social economy, low industrial "three wastes" emission and less karst groundwater exploitation. Based on the water quality data of 1950s as the initial value of groundwater pollution, this paper studies the evolution of groundwater pollution in Jinan: since 1958, with the intensification of human activities and the increase of exploitation, the water quality of karst water in urban areas, eastern suburbs and western suburbs has gradually deteriorated, and the contents of conventional components such as salinity, total hardness, chloride ion, sulfate radical and nitrate radical have shown an upward trend (Figure 4), especially the contents have increased obviously. In 2002, the groundwater content in urban area was 5.83 times that of 1958, and that of Emei Mountain Water Plant was 47 times that of 1958. Due to the exploitation of groundwater, the regional water level drops and the redox environment changes. In the whole spring area, from recharge area, runoff area to discharge area, the content of conventional components of karst groundwater generally increases. Industrial wastewater discharge causes point pollution of karst groundwater, which is serious in some areas. For example, in a well in Jingjiagou, the content is 13 13.74mg/L, and the salinity is 2544.52 mg/L. The comprehensive evaluation shows that the water quality is poor (Class V).
1959-2002 the relationship between spring flow, groundwater level, exploitation and precipitation.
1- annual precipitation; 2- annual average water level in urban areas; 3- year average spring flow; 4- Mining volume in cities and surrounding areas
Figure 4 1958 to 2002 variation curve of groundwater hardness and salinity.
1- hardness; 2— Mineralization degree
4. Analysis of groundwater exploitation potential in Jixi water source area
The developed water sources of Qiaozili, Lengzhuang and Gucheng in the western suburbs of Jinan are located in Beishahe River Basin and Yufu River Basin. In the rainy year and the rainy season, some areas drill wells by themselves, and there is potential for karst groundwater exploitation in this area. For example, in September 2004, when the water source of the ancient city was mined, the well was still self-flowing.
According to the calculation, under the condition of multi-year average precipitation, the precipitation recharge in Beishahe Basin is 9.2×104m3/d. Due to the closure of the upstream reservoir, only a small amount of surface water is replenished in the average precipitation year. Therefore, the exploitation amount of Qiaozili and Lengzhuang water sources should not be greater than 10× 104m3/d, and the water plants in the water sources of Emei Mountain, Lashan Mountain, dayangzhuang and Gucheng are far away from springs.
5 Countermeasures and suggestions for water environment protection and spring water protection
5. 1 Adjust the mining layout and implement quality water supply.
Through numerical simulation and optimization calculation (excluding agricultural exploitation), the spring water level is kept above 28.5 m in the dry season, the allowable exploitation amount of karst water in the spring area is 18.8× 104m3/d, the exploitation amount of Jixi water source is 10× 104m3/d, and the Xijiao Waterworks. These high-quality groundwater resources can be used for domestic water and complex industrial water. According to the per capita water consumption 150L/d, it can meet the domestic water consumption of 4 million people. Generally, industrial water is changed to surface water (Yangtze River water and Yellow River water), so as to give full play to the role of Qing Yu Lake and Queshan Reservoir and completely close industrial self-provided wells. On the premise of saving water, agricultural irrigation uses surface water and restricts the use of karst groundwater.
5.2 Source of supply
As Wohushan, Jinxiu Chuan, Yuezhuang and other reservoirs intercept a large amount of surface runoff, which reduces the recharge of groundwater in the spring area, changes the natural ecosystem, and directly affects the outflow of spring water, Wohushan and Jinxiu Chuan reservoirs should stop supplying water to the urban area, transform the existing main water delivery channels, and supply water to the direct recharge areas such as Xinglong, Shiqingya and Yufu River. Yuezhuang reservoir is used to supplement the North Shahe River to reduce the impact of "westward advancement" on the groundwater environment in the western suburbs; With the planning and construction of the eastern industrial belt and the eastern new city, the eastern suburbs can consider water transfer to replenish the source in the future, but the water source for replenishing the source is still in short supply.
5.3 Gradually close industrial self-provided wells
Reduce the exploitation of industrial self-provided wells in the eastern and western suburbs, and gradually eliminate the impact of drip bucket on spring water supply in economic colleges, derrick ditches, high-tech development zones and other areas.
5.4 Control the expansion of urban areas to direct supply areas.
In order to avoid the influence of urban development and construction on spring water supply, therefore, the "southern control" boundary of Jinan urban construction should be in the line of Pingandian-Pancun-Yufu Valley-Fengqi-dayangzhuang-Liu Changshan-Hero Mountain-Yangtouyu-Niuwang. Planning and construction are prohibited in the direct recharge area of karst groundwater south of the line.
5.5 Gradually harness small watersheds, strengthen afforestation and adjust the agricultural production structure in southern mountainous areas.
In the direct recharge area in the south of the spring area, it is forbidden to destroy forests to build villas, residential areas and industrial parks, as well as to reclaim land on steep slopes for quarrying. Gradually adjust the industrial structure of southern mountainous areas, implement returning farmland to forests, prohibit grazing and stop quarrying, vigorously develop forest and fruit industry, implement biological engineering, increase afforestation area, control Matiyu, Longdongyu, Dajiangou, Shiqingya, Baishiyu, Xiaolingzi, Peninsula Well, Xiajingou, Lashan and other valleys, prohibit dumping and occupation of garbage, and play a role in water conservation.
In a word, it is a complex systematic project to restore the perennial gushing of spring water, which cannot be realized in a short time through one measure. It is necessary to unify understanding, combine short-term measures with long-term goals, and implement them step by step.
Main references
Xu, Kang Fengxin. 200 1. Study on sustainable development and utilization of groundwater resources in Shandong Province. Beijing: Ocean Press.