(Chengdu Hydrogeology Engineering Geology Team, Chengdu 6 10072)
About the author: Rolling (1977—), male, engineer, mainly engaged in investigation and research of hydrology, engineering and environmental geology.
Yibin, Sichuan is located in the transition zone between Sichuan Basin and Yunnan-Guizhou Plateau. Carbonate rocks are widely distributed in this area. Supergene karst is developed in the southern Junlian karst mountainous area, with diverse and complex karst landforms and rich karst groundwater. This paper briefly expounds the hydrogeological conditions of Yuhujing underground river in Junlian from aspects of stratum water abundance, hydrogeological units and groundwater resources conditions. Taking the successful development of underground river as a water source as an example, this paper expounds its great economic and social benefits, and summarizes the experience of comprehensive development methods such as underground river water resources development and public welfare undertakings, so as to provide reference for the comprehensive utilization and development of karst groundwater resources in Junlian karst mountainous area.
Keywords: "Yuhujing" underground river; Geological background; Comprehensive development plan; Development benefit
Yibin, Sichuan is located in the transition zone between Sichuan Basin and Yunnan-Guizhou Plateau, with hilly, low-mountain, low-mountain and Zhongshan landforms from north to south. Carbonate rocks are widely distributed in the area, and karst landforms include not only karst canyons in eastern Sichuan, but also peak forests, peak clusters, stone mounds, depressions and karst canyons in karst mountainous areas in the south of the area, which are combined into various karst landforms. The diverse and complex karst landforms provide a good spatial foundation for the formation and development of karst groundwater in this area.
There is an outlet of an underground river in the karst depression in the middle of Junlian County, Yibin City. Junlian people named her "Yuhujing" and built a park called "Yuhu Park". She is the only drinking water source in Junlian County, supplying water to 40,000-50,000 residents in the county every day. Understanding the geological background conditions and successful development experience of Yuhujing underground river in this area is of great significance to the comprehensive utilization and development of karst groundwater resources in Junlian karst mountainous area.
1 Geological background of the development of "Yuhujing" underground river
The "Yuhujing" underground river originated in Lianxi and Baihe areas in the southwest of the county seat. The length of the underground river is about 6.5km, and the exit coordinates are east longitude104 30 ′ 29.6 ″ and north latitude 2810 ′ 20.4 ″. The highest elevation of the underground river basin is 84 1m, and the outlet of the underground river is 428m above sea level, which is a shallow-medium cut long ridge low mountain.
1. 1 formation rock group and water abundance
The exposed strata in the underground river basin are mainly Triassic Xujiahe Formation (T3xj), Middle Leikoupo Formation (T2l), Lower Jialingjiang Formation (T 1j) and Feixianguan Formation (T 1F). Upper Permian Changxing Formation (P2c), Longtan Formation (P2l), Emeishan Basalt (P2β), Lower Permian Maokou Formation (P 1m), Qixia Formation (P 1q) and Liangshan Formation (P 1l).
Xujiahe Formation is a set of clastic rocks with mudstone and coal. The type of groundwater is mainly clastic pore water, with less surface spring water, and the general spring water flow is 0.08 ~ 0.8 l/s; The lithology of Leikoupo Formation and Jialingjiang Formation is mainly thin to medium thick layered limestone and dolomitic limestone, mixed with karst breccia and shale. The groundwater type is carbonate fractured karst cave water, and the karst development degree is general. There are karst springs discharged along the fissure, and the spring flow is generally1~ 50l/s. Feixianguan Formation, Changxing Formation and Longtan Formation are mainly sandstone and mudstone mixed with argillaceous limestone and limestone, and the groundwater type is mainly clastic rock mixed with carbonate fissure karst water, with a general karst development degree, and the karst spring flow is 1 ~ 10L/s, with deep water cut. Emeishan basalt is a blue-gray, dark gray and dark green dense basalt, which is a relative water-resisting layer in the area.
Maokou Formation and Qixia Formation (including Liangshan Formation) are dark gray and gray-black limestone sandwiched with bioclastic limestone, which are the main karst water-bearing strata in this area. The limestone is thick and pure, and there is no layer of insoluble rock interlayer except the sand and shale whose thickness is not more than 2 1m at the bottom of Liangshan Formation. Karst in this layer is strongly developed and karst water is very rich. The flow of Daquan underground river is mostly 50 ~ 700 L/s, and the maximum is 9400 L/s. The groundwater is mainly pipeline flow, and its runoff modulus is 7.19 ~18.72 L/s km2.
1.2 Hydrogeological unit
The "Yuhujing" underground river is located near the core of the dip end of the southwest section of Junlianbi anticline and develops along the axis of the anticline. The stratum in the core of anticline is the gray and dark gray medium-thick layered limestone with bioclastic limestone in the Lower Permian Maokou Formation, Qixia Formation and Liangshan Formation, and the bottom is sand shale with thin limestone. Limestone is thick and pure, with strong karst development, forming many karst valleys, depressions and karst canyons. There are many caves and underground rivers, and karst water is very rich. The recharge area, runoff area and discharge area of Yuhujing underground river are all in this stratum. The strata on the two wings of the anticline are the Upper Permian Emeishan basalt, the Lower Triassic Longtan Formation, the Changxing Formation and the Feixianguan Formation in turn, and the Emeishan basalt is a relative aquifuge, which makes the lower Permian limestone stratum in the core form a relatively independent hydrogeological unit (Figure 1).
Figure 1 Schematic Diagram of Exposed Location of Yuhujing Underground River
1.3 Karst groundwater resource conditions
Limestone is widely exposed in Junlian karst mountain area. Supergene karst is developed, which can receive a lot of rainfall recharge. The upstream Junlian River partially infiltrates, which constitutes the main recharge source of the underground river. The underground river flows from southwest to northeast, which is basically consistent with the direction of structural lines and surface rivers; The underground river has two outlets, which are about 500 meters apart. The flow in dry season is 342L/s, and the maximum flow in flood season can reach 2000 ~ 3000 L/s ... The water quantity of underground river is affected by rainfall. The underground river basin belongs to the transitional monsoon climate zone between subtropical zone and temperate zone, with an average annual rainfall of 1 138mm, mainly from May to September, an average annual water surface evaporation of 1054mm, an average annual temperature of 17.6℃ and a relative humidity of 82%. The water quantity will increase after it rains in general recharge area 1 ~ 2 days. If there is heavy rain in the upstream, the underground river may become turbid, and it will take about 1 week to recover. The results of sampling analysis (see the table below) are HCO 3-CA type, with salinity of 286.9mg/L and pH value of 7.9. According to the Groundwater Quality Evaluation Standard (GB/T 14848- 1993), it belongs to the good water quality category.
Water quality analysis results table
2 "Yuhujing" underground river water source development project
2. 1 Development and utilization plan for drinking, irrigation and public welfare projects
The "Yuhujing" underground river has always been the water supply source of Junlian County. 197 1 year ago, no water plant was built, and residents took water by themselves, so the water quality was difficult to guarantee. 197 1 A simple waterworks was built to take water from the outlet for direct drinking. 1988 a sedimentation tank and a filtering device were built, and the water quality was improved by disinfection with alum. 1994 was disinfected with liquid chlorine, which reached the national drinking water quality standard. At present, the daily water supply capacity of the waterworks is 10000 tons, which fully meets the water demand of the county. In addition to domestic drinking, the underground river also provides industrial production water for several factories, and most of the remaining water flows into Junlian River for downstream agricultural irrigation. Only in February-March every year, there is little water and occasional water shortage, but all of them can be guaranteed to drink.
Although the development and utilization of Yuhujing underground river is simple, it has great social benefits. Yuhujing Park, built by this underground river, is a sacred place in the hearts of Junlian citizens and has feelings that cannot be abandoned.
2.2 Economic benefits of underground river development
Junlian county waterworks was built in 197 1 year, and invested by the government. The initial capital is only 40,000 to 50,000 yuan, and the facilities are simple. In the future, the investment in renovation is more than 6,543.8+0,000 yuan. At present, the water supply capacity is 2 million t, and there are nearly 654.38+0,000 employees. In 2000, the water plant was restructured, and the shareholding system was implemented, with the state holding shares and employees taking shares. The government pricing of tap water is 1.0 yuan/t. At present, the annual water supply is about 2 million t, the annual output value is about 2 million yuan, and the profits and taxes paid are about 654.38+10,000 yuan. After deducting electricity, equipment maintenance, materials and personnel salaries, the annual net profit is about 300,000 yuan.
3 Conclusion
Although the development and utilization of Yuhujing underground river is simple, it has great social benefits. In the process of development, taking advantage of the favorable conditions of underground river exposure and using local materials, the cost of underground river reconstruction project and underground river development is reduced. Underground river, as a kind of groundwater resource, has the characteristics of excellent water quality and low water temperature. In the process of development, we should give full play to the characteristics of its groundwater resources, combine the needs of regional economic development and various utilization and development methods, take advantage of its development terrain and abundant water resources, and build public welfare undertakings such as living water parks to bring its good social benefits into play.
In addition, the development and utilization of underground rivers should first carry out a detailed geological survey of the region, find out the conditions and scale characteristics of underground river development, make a reasonable planning and development plan, and avoid blind investment. The development and operation of underground rivers can be carried out in stages according to the needs of regional economic development to avoid waste of resources. Due to the influence of global warming, vegetation reduction in recharge area and mining drainage, the water volume of Yuhujing underground river in Junlian is gradually decreasing, especially in dry season. Therefore, local governments should rationally plan and utilize karst groundwater to avoid the groundwater level decline due to over-exploitation and depletion of underground rivers.
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