Problems and sustainable development of shallow groundwater development in Puyang city

Liu Yuzhong 1 Lanziting2 Song Lihong 1

(1 Henan Institute of Hydrogeology and Engineering Geology, Xinxiang, 453002; 2 Geological Survey Institute of Henan Province, Zhengzhou, 450007)

Puyang City is one of the cities in Henan Province that are seriously short of water. The main environmental geological problems caused by shallow groundwater development in Puyang city are pointed out. According to the characteristics of water resources, geological environment and social economy, this paper puts forward some countermeasures to realize the sustainable development of water resources and social economy: establishing water-saving society, implementing water-saving strategy, diverting water from the Yellow River (river) to replenish resources, adjusting the contradiction between supply and demand with economic leverage, strengthening monitoring and forecasting, and realizing the sustainable development of geological environment and social economy.

Keywords groundwater development, geological environment problems, sustainable development, prevention and control countermeasures, Puyang city

Puyang City is located in the northeast of Henan Province, with a planned area of 7 10 km2 (including Puyang County and some areas of the oilfield). It is a new regional central city based on petrochemical industry. Since 1983 was founded, with the development of urban national economy and the development of Zhongyuan oilfield, the demand for groundwater is increasing day by day. Due to the over-exploitation of groundwater, a series of environmental geological problems have been triggered, which have had a certain impact on the sustainable development of regional economy and people's lives.

1 Present situation of groundwater development

Since the establishment of Puyang city, a large number of groundwater development and utilization projects have been built, and a groundwater resources engineering system has initially formed. These projects have played a great role in improving the living standards of local people and the stable development of industrial and agricultural production. According to statistics, there are about 3000 wells/kloc-0 in the city, and the average groundwater exploitation for many years is 19302× 104m3. According to the investigation, shallow groundwater is mainly exploited for industrial and agricultural production and domestic water.

2 environmental geological problems caused by groundwater overexploitation

2. 1 The groundwater continues to decline and the descending funnel continues to expand.

Since 1980s, with the increase of dry years and the development of social economy, the groundwater exploitation in Puyang City has intensified and the over-exploitation is serious. Due to a large number of disorderly exploitation of groundwater, its flow field characteristics and dynamic characteristics have changed greatly, resulting in the continuous decline of groundwater level (Figure 1), forming a water level decline funnel centered on Puyang Agricultural Machinery Company. According to statistics, in 2002, the buried depth of the underground water level in the center of the funnel was 26.04m, and the funnel area was 183.33km2, which was 4.94m lower than 1996. The funnel area has expanded by 58.33km2, and the groundwater level has dropped by 0.62m/a on average.

Figure 1 Dynamic curve of groundwater level

According to the 8-year groundwater monitoring in Puyang City, the groundwater resources are increasingly exhausted due to over-exploitation. If we continue to develop without restrictions, it will inevitably lead to a further continuous decline in the groundwater level and a continuous expansion of the groundwater drop funnel.

2.2 Land subsidence

Over-exploitation of groundwater for years, the water level continues to drop, which destroys the rock mechanics balance of strata, reduces the pore pressure of soil layer, increases the effective stress, compresses loose soil, and causes different degrees of land subsidence in the city. According to the monitoring, the settlement center is located near the intersection of huanghe road and Jingkai Avenue, and the accumulated settlement in the central area reaches 4 1 ~ 57mm, and the difference also reaches16 mm. Under the condition that the position of the settlement center is basically unchanged, the settlement area continues to expand, and there is still a tendency to continue to expand. The increase of uneven settlement means that the risk of geological disasters is also increasing, which has great potential harm to ground buildings and underground pipe networks and cannot but attract people's attention.

2.3 groundwater resources attenuation, aquifer drainage

According to geological data, the floor of the first aquifer (Q4) of shallow groundwater in urban areas is buried at a depth of 24 ~ 30m. In the urban area, the first aquifer will be drained. At present, 80% of the shallow pumping wells 30 meters north of Jindi River have decreased drainage efficiency and pumped water, and 20% have dried up. Some mines have replaced new pumps because of pumping water, which has caused great economic losses. According to the survey, the exploitation amount of shallow groundwater reaches 19302× 104m3/a, the exploitation modulus is 27.2×104m3/(a km2), and the exploitation intensity in urban areas reaches 50.8×104m3/(a km2). If groundwater is exploited without restriction, it will inevitably lead to the shortage of groundwater resources and other more serious environmental geological problems.

2.4 ground fissures

Ground fissures refer to linear cracks in rock mass or soil that extend to the surface. 1997 July-August, due to the continuous drought, a large number of groundwater was exploited, and the groundwater level dropped sharply. There are three ground fissures in Daliushu-Fengzhai-China-Jiji area and Liuwen township in Huxiang county, Puyang county, with a total length of about 2570m, a width of 5cm and a measurable depth of1.75 m. However, with the increase of groundwater level, the development of the fissures has been controlled. When the field investigation was conducted again in July 2000, it was found that the cracks no longer developed. At this time, due to abundant rainfall, the groundwater level rose sharply, indicating that serious over-exploitation of groundwater is the main cause of ground fissures.

3 causes of environmental geological problems

Among natural factors and human factors, human factors are the fundamental factors that cause environmental geological problems.

3. 1 natural factors

On the stratum, thick silt and silty clay are deposited in the study area, with an average thickness of 29.5 ~ 52 m; However, the compressibility of cohesive soil layer is higher than that of sandy soil layer, and the porosity is also higher, so it is easy to be compressed. Therefore, the existence of thick silt and silty clay is the premise of land subsidence. Since 1980s, the decrease of precipitation and the increase of dry years are also one of the reasons for geological disasters.

3.2 Human factors

At present, the shallow groundwater exploitation in Puyang planning area is the target layer, and the deep groundwater exploitation is very few, accounting for about 20%. With the economic development of Puyang City and the development of Zhongyuan Oilfield, the mining mode has also changed from decentralized mining to centralized mining. At present, the mining modulus reaches 27.2×104m3/(a km2), and even reaches 50.8× 104m3/ in urban areas. With the development of the funnel of groundwater level decline, the land subsidence is also developing. Considering the lag of land subsidence, the shallow groundwater isolines in May 1996 and May/2000 are compared with the accumulated isolines of land subsidence in May 1997 ~ 200 1 year (see Figure 2). It can be seen that the range of the landing funnel is highly consistent with the range of land subsidence, and at the same time, the land subsidence occurs in areas where the groundwater level drops greatly. In some areas, the cumulative isoline of land subsidence is almost parallel to the isoline of groundwater level decline, but there is basically no land subsidence near the "Yilong" ground reservoir in the southwest corner of the planning area, which shows that: ① whether the groundwater level drops sharply in the planning area has a great influence on the occurrence of land subsidence; ② The infiltration and recharge of surface water can slow down the occurrence and development of land subsidence.

Fig. 2 Correlation analysis diagram of shallow groundwater level fluctuation and land subsidence in the planning area

Based on this, it is considered that the main cause of environmental geological problems is that the groundwater level continues to drop sharply due to over-exploitation of groundwater, forming a downward funnel and making it exist for a long time. Therefore, how to control groundwater exploitation scientifically is the fundamental point to control environmental geological problems in the future.

4 sustainable development and preventive measures

Sustainable development means that contemporary people do not seek development at the expense of consuming or even destroying the resources, ecology and environment on which the next generation depends for survival and development, maintain biodiversity, make resources sustainable, and make ecology and environment suitable for human habitation, life and work.

Because the geological environment deteriorates to a certain extent, it may evolve into geological disasters, and the occurrence of geological disasters is closely related to the changes in the geological environment. Therefore, for the geological environment problems caused by the increasingly prominent contradiction between supply and demand of water resources in Puyang City, the way to solve the problems lies in comprehensive management from the characteristics of water resources, environment and social economy, and paying equal attention to opening up sources and reducing expenditure, so as to realize the sustainable development of regional economy in the new century.

4. 1 Strengthen legal system construction, strengthen law enforcement, and correctly handle the relationship between geological environment protection and economic development.

Widely publicize the relevant laws and regulations of the state, improve the people's legal concept, and make the people care about and supervise the protection of geological environment. Protection is for development, and development promotes protection, which is the concrete embodiment of sustainable thought. Correctly handling the relationship between them can promote the sustainable development of economy and geological environment.

4.2 Establish a water-saving society and save water resources.

In the foreseeable future, the situation of water shortage in Puyang will continue to exist, so we must put water conservation in the first place and strive to improve the utilization efficiency of water resources. Agriculture is a big water user with great water-saving potential, so we should develop agricultural water-saving irrigation according to local conditions, such as: canal lining can save water by 30%, sprinkler irrigation can save water by 30%, and drip irrigation technology can save water by about 50%. New water sources should be selected for oil fields and urban industrial water. Strengthen sewage treatment, increase the secondary utilization of reclaimed water, adjust the contradiction between supply and demand with economic leverage, fully implement the water-saving strategy, and strive to achieve the coordinated development of geological environment and economy.

4.3 Artificial Recharge-Diversion from Yellow River to Jiyuan

Artificial recharge is an effective means to control the falling funnel, with simple method and feasible technology, which can exert the comprehensive effect of water storage and energy storage. Puyang City is adjacent to the Yellow River in the south, and the Puqing South Main Canal and the South Small Dike Water Delivery Main Canal run through the north and south, especially the Puqing South Main Canal runs through the funnel and the settlement center area, which has excellent conditions for water diversion from the Yellow River. However, it is also difficult to implement. First, the artificial recharge project is large, and the recharge and controlled mining should be carried out at the same time, which requires government intervention and coordination; Second, in order to prevent groundwater from being polluted, the quality of reinjection water source should not be lower than the current situation of local groundwater quality. At present, on the basis of existing work, we should select suitable hydrogeological sections, establish a test site for artificial groundwater recharge, conduct scientific experiments, and gradually carry out artificial groundwater recharge in a planned and step-by-step manner.

4.4 Strengthen the construction of forecasting and early warning system

Further improve the groundwater monitoring network, adjust and optimize the monitoring structure, improve monitoring means, speed up the construction of monitoring information network, strengthen monitoring and forecasting, adhere to the principle of putting prevention first and combining prevention with control, take remedial measures in time when problems are found, and realize the dynamic management of groundwater resources.

refer to

[1] Yan Hongqing, et al. Monitoring Report on Geological Environment of Puyang City, Henan Province (1996 ~ 2003)[ Internal data]. Hydrogeological Engineering Geological Team of Henan Bureau of Geology and Mineral Exploration and Development, 1997 ~ 2004.

[2] Wu,, et al. Investigation report on land subsidence in the planning area of Puyang City, Henan Province [internal data]. In 2002, the first hydrogeological engineering geological team of Henan Provincial Bureau of Geology and Mineral Exploration and Development.

[3] Zhou Tianyong. Development economics course. Beijing: China Financial and Economic Press, 2002.