(1. Sichuan Geological Survey Institute, Chengdu 610081; 2. Chengdu Hydrogeology Engineering Geology Team, Chengdu 6 10072)
Based on the stratum lithology, geological structure, topography and geomorphology of Yanyuan Basin, this paper analyzes the occurrence conditions and groundwater resources characteristics of Maba Longtang Underground River, expounds the successful development of Maba Longtang Underground River in Yanyuan and its great economic and social benefits, and summarizes the experience of comprehensive development of groundwater resources and cold water cultivation, which provides a reference for the comprehensive and effective development and utilization of karst groundwater and underground river in Yanyuan Basin.
About the author: Yan Yi (1954-), male, professor-level senior engineer, mainly engaged in the investigation and research of hydrology, engineering and environmental geology.
Key words: Yanyuan Basin; Maba Longtan underground river; Occurrence conditions of underground rivers; Water resources development
Maba Longtang Underground River is located in Yanyuan Basin, Yanyuan County, Liangshan Prefecture, Sichuan Province. Yanyuan basin is a plateau fault basin, surrounded by high mountains, with strong terrain cutting and large height difference, with an altitude of 3000 ~ 4000 m; There are mostly ridges and terraces in the basin, with an altitude of 2350 ~ 2700 m and multi-level planation. Moluogangzi, the highest peak in the north of the basin, is 4393.3m above sea level, and the lowest point is the Meiyu River exit in the southwest of the basin, with an altitude of 2300 m; At the edge of the basin and the foothills, the river slope is large and the water flow is fast, and the valley is mostly V-shaped. At the bottom of the basin, the river twists and turns with a small slope of only 2 ‰ ~ 3 ‰ and the water flow is gentle. Although the surface water system in this area is relatively developed, due to the dry climate, concentrated precipitation, severe evaporation and serious leakage in limestone areas, most of the surface water in the basin has the characteristics of short source, little water and no water in dry season. Surface water and groundwater in mountainous areas around the basin are collected and discharged to the middle and southwest of the basin, forming a number of centralized discharge areas, and the surrounding area of Maba Longtang is one of the main discharge areas at the bottom of Yanyuan Basin. Therefore, it is of great significance to analyze and study the occurrence conditions and comprehensive development and utilization experience of Maba Longtang underground river for the rational development and utilization planning of karst groundwater in Yanyuan Basin.
Analysis of occurrence conditions of 1 Maba Longtang karst underground river
Maba Longtan Underground River is located in Yanyuan Basin, Sichuan Province, with east longitude10130' 22.6 "and north latitude 27 34'1.5". Originated in Maidiwan and the second floor of Dahe Township, it flows south and west, with a length of about 10km, and its outlet is located in Ganhai Township. The nearby Xiaolongtang, Niufengkou and the left and right longan are all drains of underground rivers. The flow from Dalongtang exit to Maba River is about 300m, and the dark river water is directly discharged into the river.
1. 1 Strata and lithologic conditions are the basis for the formation and development of karst underground rivers.
The exposed strata in Yanyuan Basin are mainly sedimentary rocks, mainly including Mesozoic Triassic and Cenozoic Paleogene, Neogene and Quaternary strata, but lacking Jurassic and Cretaceous strata. Middle Triassic Tang Yan Formation (T2y) is grayish green, yellowish green, light gray siltstone, shale, marl, argillaceous limestone and argillaceous dolomite, with obvious multi-rhythmicity. Middle Triassic Baishan Formation (T2b) is gray-dark gray thick massive limestone mixed with dolomite limestone; Upper Triassic Lower Boda Formation (T3xb) is siltstone and marl; The Paleogene Hongyazi Formation consists of conglomerate, glutenite and lenticular coarse sandstone. Quaternary Holocene () gravel layer and clayey silty gravel layer.
The bottom of the basin is mainly covered by tertiary and quaternary strata, and Triassic carbonate or carbonate-detrital rocks are mainly exposed at the edge and foothills of the basin, among which the limestone of Baishan Formation is the most widely exposed. Carbonate rocks occur in "pure stratotype" with a thickness of tens to hundreds of meters. It is the most important water-bearing rock group in this area, with karst development and rich water content, which provides a good basic condition for the formation and development of karst springs and underground rivers in Yanyuan Basin.
Figure 1 Schematic diagram of development position of underground river in Maba Longtang, Yanyuan Basin
1.2 geological structure conditions
Fig. 2 Schematic diagram of section of underground river in Longtan, Maba.
Yanyuan area belongs to the "mountain" substructure system of Yanyuan (Figure 2). The top of the arc is located in the south of Meiyu Town, Yanyuan County, and the structure is sharply deflected from northwest to west, showing a natural arc protruding to the south. The ridge is located in the northern part of the basin, and consists of Triassic tight folds such as Yuanmuchang syncline, Zumu syncline and Sanchahe syncline, as well as nearly N-S trending compression zones. The core of Yuanmuchang syncline 10 is composed of the upper Boda Formation, while the axes of Zumu anticline and Sanchahe syncline turn sharply from northeast to northwest, forming a tight arc protruding south. Horseshoe-shaped shield is composed of relatively open composite folds and Kuzhuba faults, such as Panjiagou syncline and Madaozi anticline, and there is a relatively stable area inside the arc top from Meiyu to Acropolis. The uplift end of Panjiagou syncline is located in the northeast of the basin, extending to the southwest, passing through Panjiagou to Dashuitang, covered by Quaternary, with an axial northeast of 30 ~ 40. The core is composed of Boda formation strata, and the two wings are middle and lower Triassic strata with an inclination angle of 40 ~ 80. Secondary folds such as Baishan syncline, Gubaishu anticline, Bamiro syncline and Dayuanzi anticline associated with the two wings form a relatively gentle structure. Madaozi inversion anticline is covered by Quaternary from Madaozi near Shangganhai in Lala Mountain to the south, with an exposed length of about 22 kilometers and a fold strike of 30 NW. Its core is composed of Tang Yan Formation of Middle Triassic, and its wings are composed of limestone of Baishan Formation with an inclination angle of 40 ~ 80.
The main structures in the catchment area of underground river are compound anticline and fold structure system. The distribution of fold structure, the development depth of fault system, the nature of structural plane and the activity of near-earth objects provide migration channels for groundwater and control the distribution pattern and runoff direction of Daquan and underground river. Maba Longtan underground river is formed in the northeast of "mountain" structure, in the north of Panjiagou compound syncline, in the area of Pingba anticline and Dagou syncline. Various complex fold structural systems and composite anticline structural units control the recharge, runoff, discharge and occurrence of Longtan underground river (Figure 3).
Fig. 3 Overview of the secondary structural system of Yanyuan "Mountain"
1- compressive fracture; 2- compression-torsion fracture; 3- Tensile and torsional fracture; 4- Tensile and torsional fracture; 5- Fault of unknown nature; 6- tensile fracture; 7- anticline; 8— Inverted anticline; 9- fornix anticline; 10- syncline; 11-short axis inclination
Fracture number and name: ① tensile fracture of Shuicaoba; ② Madaozi compression fracture; ③ Compression fracture of small mountain; Tensile and torsional fractures of Maba; ⑤ Kuzhuba is crushed and broken; ⑥ Mianya tension-torsion fracture; ⑦ Hall flat compression-torsion fracture; ⑧ Maijiaping compressive-torsional fracture.
Fold number and name: 1- Mopanshan syncline; 2- Dawanzi syncline; 3- Qingshanzhai anticline; 4-Lingguantai anticline; 5— Huahonggou syncline; 6- Shangbaishan anticline; 7- Panjiagou syncline; 8— Pingba anticline; 9— Dagou syncline; 10-hat-shaped skull anticline; 1 1- gourd mouth syncline; 12-Paomaliangzi anticline; 13-Luoshuixia syncline; 14-Guliangzi anticline; 15-Sanchahe syncline; 16- Zumu anticline; 17-sheep pasture syncline; 18-Yuanmuchang syncline; 19 —— Wawugou syncline; 20— Madaozi anticline; 2 1- stinking pond syncline; 22— Xishan Huopu syncline; 23— Daqing Syncline
1.3 landform difference is the dynamic condition for the formation of underground river.
Longtan underground river recharge area is mainly located in terrace dam, and its northeast planation plane is 2600m m. The exposed limestone of Baishan Formation and conglomerate layer of Hongyazi Formation have vertical surface karst forms such as sinkhole, funnel and subsidence. The development density is 10 ~ 15/km2, which provides good conditions for a large amount of atmospheric precipitation to directly and rapidly recharge groundwater. Precipitation is the main source of groundwater recharge, and the change of underground river flow is basically consistent with rainfall. In addition, the massive infiltration of Cooper River is also an important source of groundwater recharge. The direction of underground river runoff is northeast to southwest, and the maximum runoff length can reach more than 10km. The entrance elevation of the underground river is 2450m, the exit elevation of Dalongtang is 2389m, the height difference is about 6 1m, and the hydraulic gradient of the underground river is about 6‰.
2 characteristics of underground river water resources
Dalongtang is the main drainage outlet of underground river, located on the left bank of Maba River. There are seven outlets in the north and west of Dalongtang, and five outlets in the south, including left and right longan and cow draft. Among them, right longan flows out from the right bank of the river across Maba River, and the whole drainage bandwidth is about 1km.
Because the underground river mainly comes from atmospheric precipitation and Cooper River, the groundwater runoff alternates quickly, and the rainfall in the upper reaches can only be displayed at the outlet of the underground river after several hours or even longer, which shows that the water yield increases, the water quality becomes turbid, and it becomes clear a few days to ten days after the rainfall stops. The average annual rainfall in the underground river basin is 779mm, mainly concentrated in June 6- 10/0 (Figure 3). According to the sampling analysis (see the table below), the groundwater in Dalongtang is HCO 3-CA type water, with salinity of 179. 1mg/L and pH value of 8.2, which is weakly alkaline. According to the Groundwater Quality Standard (GB/T 14848- 1993), it is inferior. Other water outlet points are HCO 3-Ca or HCO 3-Ca/mg, and the salinity is 200 ~ 300 mg/L, which are excellent, good and poor respectively. It is estimated that it is related to its own process and self-purification. The smaller the general flow, the better the water quality, and the smaller the dynamic change of flow.
Water Quality Analysis Results of Dalongtang Underground River
3. Development project of underground river water resources in Maba Longtang, Yanyuan Basin
3. 1 cold water fishery breeding, flood regulation and water storage development and utilization scheme
Maba Longtang Underground River originates from Maidiwan and two floors in Dahe Township and flows south to west, with a length of about 10km. The outlet is located on the left bank of Maba River in Longtang Village, Ganhai Township, forming a centralized drainage zone, in which the discharge of Dalongtang is the largest, reaching 8290 L/s, generally 1000 ~ 5000 L/s, and nearby Xiaolongtang, Niufengkou and left and right longan are the drainage outlets of underground rivers. The flow from Dalongtang exit to Maba River is about 300m, and the underground river is directly discharged into the river (Figure 4).
Fig. 4 Long-term dynamic curve of groundwater in Maba Longtang.
The outlet of Dalongtang Underground River is at a low altitude, only about 12m higher than the water surface of Maba River. After flowing about 300 meters, it flows into a river that has not been used for many years. Since 1960s, it has been planned to build a reservoir (Longtang Reservoir) in the valley area about 1km downstream of the underground river outlet. 1995, the government of Yanyuan County built Shuangshibao Reservoir about 600 meters downstream of the original design dam site in the form of work instead of relief, with a water storage elevation of 2,380 meters. The capacity of the reservoir is much smaller than that of the original Longtan Reservoir. It can store water in the dry season, irrigate dozens of hectares of grain fields downstream, and provide drinking water for people and livestock, greatly alleviating the water shortage problem in the dry season. The reservoir water mainly comes from the groundwater of Maba River and Longtan, and the reservoir water is mainly supplied by underground rivers in the driest season.
In 200 1 year, Gao, a villager from Group 5 in Longtang Village, Ganhai Township, and two other villagers invested about 1.5 million yuan to build a four-stage cofferdam below the exit of Dalongtang. The outlet of the cofferdam is blocked with fine steel wire mesh to build a living water fish pond, and the lowest level cofferdam is just the same as the highest water level of Shuangshibao Reservoir. Cofferdam has a certain water storage capacity and sufficient flood control capacity to ensure the safety of fry. Because the temperature of the underground river is kept at 16℃ all the year round, it is most suitable for breeding cold-water fish (also known as soft-shelled turtle). The underground river has a large amount of water in summer, which can carry a lot of nutrients, and it has a small amount of water in winter, which is convenient for breeding. Cold-water fish is famous for its tender meat and delicious taste. Its growth is slow, and it usually takes 3 ~ 5 years to grow to about 0.5kg. At present, the market is in short supply.
3.2 Economic benefits brought by underground river development
The development and utilization of underground river water has brought great economic benefits to the local area. After the completion of Shuangshibao Reservoir, most downstream areas such as Liunibao, Racecourse, Liushuwan Village and Meiyu benefited, which alleviated the problem of drought and water shortage in winter and spring, ensured drinking water for people and livestock in winter and water for spring ploughing in the coming year, and stabilized people's hearts, with great economic and social benefits.
The investment of fish culture in the cofferdam of Dalongtang underground river is about 6.5438+0.5 million yuan, and the fine-boned fry is about 700kg. According to the calculation of 60 yuan/Jin, the fry cost is about 42,000 yuan, and corn is used as feed. So far, the investment is close to 250,000 yuan. After three years of cultivation, some fry can grow to more than 0.5 kg and can enter the market for sale. According to the four-year culture cycle, about 5000 kilograms of adult fish can be produced by 2006. Based on the current market price 1.20 yuan/kg, the sales income can reach 600,000 yuan. Excluding the investment of nearly 300 thousand in the early stage, you can earn nearly 300 thousand, and the annual rate of return can reach 60 thousand yuan. In the future, the annual profit will increase year by year, and the economic benefits will be very considerable.
4 conclusion
The development and utilization of underground river water resources in Maba Longtan is not only used for water storage irrigation, but also for developing cold water fishery culture according to its water resources characteristics such as low water temperature and good water quality, so as to give full play to the characteristics of underground river water resources. Carbonate rocks are widely distributed in Yanyuan Basin, limestone strata are karst, and there are many karst springs and underground rivers exposed. The successful development of Longtan underground river provides a reference for local governments to comprehensively develop and rationally utilize karst groundwater. The karst conditions in Yanyuan basin are complex, and the geological environment conditions in each basin are different, so the development and utilization of groundwater cannot adopt the same model. Instead, according to the characteristics of groundwater in each basin and the local economic and geographical conditions, the development plan should be formulated according to local conditions to maximize its role.
refer to
Sichuan Geological Survey Institute. 2005. Investigation of karst groundwater and environmental geology in key areas of Sichuan.
China People's Liberation Army 0093 1. 1978. Regional hydrogeological survey report (scale1:200,000) (Yanyuan Sheet)
Sichuan Geological Survey Institute. 2003. Investigation Report on Groundwater Resources and Eco-environmental Geology in Karst Mountainous Areas of Sichuan (South Sichuan and Panxi)
Liu Junxian, Ge Wenbin. 2002. Selected Papers on Groundwater Exploration in Severe Water Shortage Areas. China geological survey. Study on deep circulation of karst groundwater in Sichuan [C].
Karst Research Group, Institute of Geology, Chinese Academy of Sciences. Study on Karst in China [M]. 1979. Science press.
Liu Minsheng. 2004. Analysis of circulation mode of deep karst groundwater in Sichuan Basin and its surrounding areas [J]. Geological disasters and environmental protection, (2): 49 ~ 5 1.
Research group on comprehensive development of carbonate areas in Sichuan Province. Investigation on the present situation of carbonate rock areas in Sichuan Province and research report on the ways of development and utilization
Chengdu Hydrogeological Engineering Geological Team of Sichuan Bureau of Geology and Mineral Resources. Distribution map and explanation of Daquan (underground river) in Sichuan