Study on Development and Utilization of Jumu Underground River Water Resources in Guizhou Province

(Guizhou Bureau of Geology and Mineral Resources, Guiyang 550004)

Abstract: Jumu underground river basin is one of the typical representatives of underground rivers in bare karst mountainous areas in southern Guizhou. There are not only abundant groundwater resources in the basin system, but also eco-environmental problems such as karst drought, karst flood and rocky desertification caused by fragile karst environment. Based on the results of the project "Demonstration of Groundwater Development and Geological Environment Improvement in Typical Watershed of Guizhou Province", this paper explores and summarizes the ways to improve the ecological environment of the watershed with groundwater development as the leading factor, and puts forward the development and utilization planning of underground rivers, which is of guiding significance for the development and ecological environment improvement of similar underground rivers.

Key words: underground river basin; Groundwater development; Ecological environment management; study

Jumu Underground River is developed in the plateau slope zone from Guizhou Plateau to LAM Raymond Plain in Guangxi, and it is one of the tributaries of large, medium and small underground river systems in karst valley of peak cluster depression in southern Guizhou, with a total basin area of 128.4km2, where karst is strongly developed and surface water resources are scarce. The geological environment problems dominated by rocky desertification are more prominent and the ecological environment is fragile. Tangbian and Kedu Town, Pingtang County, located in the lower reaches of the underground river estuary, have become national key poverty alleviation areas, although the terrain is relatively flat and the population and cultivated land are concentrated. Among them, engineering water shortage is an important reason why its social and economic development level is relatively backward for a long time. Up to now, about 667hm2 of cultivated land in this area is still "Wang Tiantian", and there are still more than10.6 million rural population and10.0 million large livestock that are short of water. Therefore, the research and development of Jumu underground river is of great significance for improving the local ecological environment and promoting social and economic development, and also has strong guiding significance for groundwater development in the same type of underground river basin.

1 Geological conditions and karst development characteristics

The exposed strata in Jumu underground river basin are the Lower Permian Maokou Formation (P 1m) and Qixia Formation (P 1q), the Upper Carboniferous Maping Formation (C3mp), the Middle Huanglong Formation (C2hn), and the first and second members of the Lower Datang Formation (c1d1q). Among them, the first member of Datang Formation and Wujiaping Formation are clastic rocks, and other strata are carbonate rocks.

The structural position of Jumu underground river basin is the composite part of gentle Yashui anticline and Kedu syncline, and the dip angle of rock stratum is gentle. The development of NE-trending faults and two groups of NE-and SE-trending "X"-shaped joints in the area controls the distribution pattern of underground river pipelines in the system. Along the extension direction of underground river pipeline, the individual forms of karst such as skylight, shaft, karst cave, karst depression and sinkhole are densely distributed, and the karst depth and superposition characteristics are obvious.

2 characteristics of underground river system

2. 1 system plane structure

Jumu underground river system is dendritic in plan, and consists of three tributaries: reaching the pond, searching for nests and mixing in the west (Figure 1).

Figure 1 Hydrogeological Schematic Diagram of Jumu Underground River Basin

1- watershed boundary; 2- Underground river outlets and pipelines; 3- Underground river skylight; 4- vertical axis; 5— Karst pool; 6- groundwater flow direction; 7— Stratigraphic code and stratigraphic boundary; 8— Faults of unknown nature and presumed faults; Jiuanticline

(1) reaches the tributary of the pond. Runoff flows from northwest to southeast. Clastic strata and carbonate strata are alternately distributed in the upper reaches, and underground rivers are alternately bright and dark; Undercurrent surges in the exposed area of carbonate strata in the middle and lower reaches.

(2) Wangwo tributary. The underground river passes through carboniferous carbonate strata of Datang Formation (C 1d), Baizuo Formation (C 1b), Huanglong Formation (C2hn) and Maping Group (C3mp), and the whole process is subsurface flow with deep groundwater level. Along the underground river pipeline, the surface karst depressions are arranged in a beaded pattern, and funnel-shaped depressions and sinkholes are densely developed.

(3) West mixed tributaries. Runoff flows from north to south, with open flow and undercurrent alternating frequently along the way. The topography of the upper reaches of the basin is relatively gentle, and the landform combination type is peak cluster valley. The groundwater level in the valley is shallow, and there are many natural water intake points such as wells, underground river skylights, underground river outlets and undercurrent inlets. From the middle and lower reaches to the exit section, all underground rivers become undercurrents.

The tributaries of the Jumu underground river system gather in the flooded depression under the dam in the lower reaches of the basin. Among them, tributaries reaching the pond and Wangwo are discharged into Jumu Village, which is called Jumu Underground River in a narrow sense, with a drainage area of 83km2. Xihe underground river discharges at the foot of the big hole, with a discharge area of 45.4km2 and a distance of 0.4km between the two outlets.

2.2 system space structure

Along each tributary pipeline of Jumu underground river system, there are many underground river skylights and wells developed on the surface, which are connected by underground corridors and caves, and the development scale is several meters to tens of meters high and dozens of centimeters to tens of meters wide. Their spatial forms are complex and changeable, some are deep pools, while the floodplains at the confluence of tributaries form a network (Figure 2).

From June 5, 2004 to 10, an underground river tracing experiment with salt as tracer was carried out in the lower reaches of Jumu underground river system. The time-duration curve of Cl- mass concentration detected in groundwater at the outlet of underground river is multi-peak and slow (Figure 3), which reflects the multi-branch and network characteristics of underground river system. However, the decay time of Cl- mass concentration is long, which reflects that the hydraulic gradient in the experimental section of underground river is gentle, and there is pool-like water storage space in the middle and lower reaches of underground river. It can be inferred that the underground river pipeline space in the middle and lower reaches of Jumu underground river system consists of many irregular corridors, dissolved pools and dissolved cracks.

Fig. 2 Schematic diagram of underground pipe network in flooded depression

1- main groundwater pipeline; 2- Underground river branch pipe; 3- Depression boundary; 4- Underground river entrance; 5- Underground river exit; 6- water axis; 7- Falling Water Cave

2.3 hydrodynamic characteristics of groundwater in the system

Through the analysis of the longitudinal section of the middle and lower reaches of underground river (Figures 4 and 5):

(1) west mixed tributary. The water level of the west mixed valley is 845m, the dam is 840m, and the outlet water level of the underground river is 815 m; The distance between the west mixed valley and the submerged dam valley is 2. 1km, and the hydraulic gradient is 2.38 ‰. The length from the submerged dam valley to the outlet of the underground river is 1.4km, and the hydraulic gradient is 17.9‰.

(2) Reach the tributary of the pond. The ground elevation of Lashan gully is 850m, and the water level elevation in the gully is 845m. The distance from the skylight of underground river KS309 to the outlet of underground river is 4.05km. After dosing, the first reagent peak detection time is 197. 1 hour, and the last peak appears at 700.8 hours after dosing. From this, it is calculated that the velocity of underground river is 138.70 ~ 488 m/d, with an average of 365438+.

The test period is "level period", and the test results show that the groundwater velocity in the middle and lower reaches of the underground river system is slow, similar to "laminar flow". At the same time, it also shows that the strongly developed underground river network space has strong storage and regulation ability for groundwater resources.

2.4 Dynamic characteristics of groundwater and water resources in the system

Atmospheric precipitation is the main source of groundwater recharge in Jumu underground river system, and its outflow curve is irregular multi-peak and zigzag with the change of precipitation (Figure 6), which has typical meteorological characteristics. After several days of heavy precipitation, the outlet flow rose to the peak, and then began to decline in a short time. The maximum discharge in May-June of the year is 7.23m3/s, and the minimum discharge in March of the following year is192.87L/s.. The annual average flow rate is 83 1.88L/s, and the annual change rate is 37.5 times.

In the middle and late September, the outlet flow of Jumu underground river entered a decay period, which lasted for about 200 days until the rainy season came in the late April of the following year. Based on the dynamic long-term monitoring sequence data, the flow attenuation equation of underground river is established;

Fig. 3 Variation curve of mass concentration of Clˉ in the comprehensive test of Jumu underground river.

Fig. 4 Schematic diagram of longitudinal section of S73 skylight to exit section of Xixi underground river.

Fig. 5 Schematic diagram of longitudinal section from skylight K309 to Jumu underground river exit.

Fig. 6 Dynamic curve of outlet flow of underground river

1-flow process curve; 2- precipitation process curve

Qt = q0e 1-0.009 14t( 1)

Using the formula (1) to integrate the groundwater flow in the whole underground river system consumption process, the groundwater regulation resources of the underground river system can be obtained.

Development and Utilization of Karst Groundwater Resources in Southwest China

QIt takes the flow of 478. 19L/s at the beginning of the attenuation period on September 30th, and Qt+ 1 takes the flow of 2 14.52L/s at the end of the attenuation period on April 20th, and calculates α = 0.009 14, and finally obtains v = 3.

2.5 Ecological environment characteristics

Throughout the whole region, the landforms above the underground river outlet are all peak-cluster depressions, and the upstream population and cultivated land are sparsely scattered in some small karst depressions, with no surface water body and deep groundwater level; The scale of karst valleys and depressions in the middle and lower reaches is large, with dense distribution of cultivated land and population. Underground rivers are mostly alternating with light and shade, and the groundwater level is shallow but dynamic. The terrain below the underground river exit is gentle, the cultivated land is contiguous, the villages and population are dense, and the villages, towns, businesses and grain-producing areas are integrated. The elevation of the surface riverbed is low and it is difficult to use.

Karst drought, karst flood and rocky desertification are the most important ecological and environmental problems in this basin.

(1) karst drought. Everywhere in the whole river basin. Due to strong karst and serious surface leakage, there is a shortage of irrigation water for cultivated land and drinking water for people and livestock, especially in the Kedu-Tangbian Valley below the outlet of underground river. About 667hm2 of cultivated land is short of irrigation water, 1.6 people and 1 10,000 large livestock are short of drinking water (photo 1).

Figure 1 Drought dam downstream of huge underground nuclear outlet

(2) Karst flood. The main causes of the disaster are the slow hydraulic gradient of groundwater, the large recharge in the upstream of the system in rainy season, the backwater after the groundwater level rises from the downstream to the outlet, and the insufficient discharge capacity of underground river pipelines, which leads to the flooding of karst valleys and depressions. Typical examples are the flooded dam depression and the west mixed valley in the middle and lower reaches of the basin, in which the continuous flood disaster has forced about 67hm2 ~ 2 of cultivated land in the flooded dam depression to be abandoned (photo 2). According to the dynamic monitoring data of the outlet flow of Jumu Underground River, the maximum flood discharge capacity of the underground river in the outlet section of the underground river is 7.23m3/s, and when the upstream inflow exceeds this value, depressions and valleys such as overflow dams will be submerged.

Photo 2 Flood-flooded dam

(3) rocky desertification. Sporadic distribution in the system, but in the middle and lower reaches of the river basin and Jiao Gang and other large limestone distribution areas below the underground river outlet, rocky desertification is more serious, and it is mainly severe.

3 groundwater development and utilization conditions

Due to the scarcity of population and cultivated land, the water demand in the middle and upper reaches of the system is relatively small, and the drinking water for people and livestock and irrigation water for farmland is mainly distributed water supply. Therefore, we can make full use of the underground outlet, open flow section, underground river skylight, well and numerous surface karst springs distributed along the underground river runoff.

In the middle and lower reaches of the system and below the underground river outlet, the distribution of cultivated land and population is relatively concentrated, and the water demand is large. The tributaries of the system gather in the overbank depression, which is rich in water and has a large underground space capacity, and the underground hydraulic gradient from the overbank depression to the exit section is large. Therefore, the groundwater level difference and the storage capacity of underground space can be used to store water to build underground reservoirs, and at the same time, groundwater resources can be comprehensively developed through engineering measures such as water lifting and pumping.

4. Overall planning for the development and utilization of Jumu underground river

4. 1 Guiding ideology of underground river development

The guiding ideology of giant underground river development is not completely equivalent to the traditional "water resources" development. The basic idea of its development and utilization is that groundwater development should be closely combined with national goals such as rocky desertification and flood disaster control, land consolidation and poverty alleviation and development. In terms of engineering measures, it is necessary to combine the groundwater development project with the ecological environment protection and treatment project according to local conditions, and explore ways to improve the ecological environment of the basin with the development of underground rivers as the leading factor.

4.2 the principle of underground river development planning

The middle and lower reaches of the system and the areas below the exit are the key beneficiary areas for the development and utilization of Jumu underground river. According to the characteristics of basin geological environment and the conditions of underground river development and utilization, its development and utilization should follow the following principles:

(1) principle of economic feasibility. Groundwater development projects should strive to save investment and low operating costs, use gravity water diversion for farmland irrigation as much as possible, and avoid electric machinery to lift water.

(2) The principle of adjusting measures to local conditions. Make full and reasonable use of surface and underground karst space and make full use of precious karst water resources.

(3) The principle of comprehensive utilization of engineering means such as "lifting, pulling and storing".

(4) The principle of combining the development of groundwater resources with the improvement of ecological environment.

4.3 Overall scheme of engineering design

The overall scheme of underground river development consists of two parts: groundwater development and utilization project and ecological environment control project.

(1) groundwater development and utilization project. According to the characteristics of strong water storage capacity of underground space in the basin, large annual average flow of underground river but low elevation of outlet, karst drought downstream of outlet, karst flood upstream, and small ground elevation difference between dry dam and flood valley, the design of groundwater development project is mainly to improve the water level of underground river, supplemented by water storage. The water storage project mainly uses underground space to build dams and reservoirs at the outlet of underground rivers. The design elevation of dam crest fully considers that the difference between the elevation of underground river outlet (8 15m) and the elevation of submerged dam depression (845m) is only 30m. In order to avoid the inundation caused by the backwater level in the reservoir area being higher than the flooded dam depression, the water storage elevation of the underground reservoir is limited to 830m m. When the water level of the underground reservoir rises to an elevation of 830 meters, it can be used to irrigate the cultivated land below the pond downstream of the outlet of the underground river and below the elevation of 825 meters in Kedu Valley. Construction of hydraulic pump station at the dam of underground reservoir to pump water for people and animals in downstream market towns and villages; In order to make up for the shortage of regulated storage capacity caused by the limited storage elevation of underground reservoir, a dam was built at the surface valley 1.2km downstream of the outlet of underground river, and the water from the outlet of underground river was stored to form a secondary regulated storage reservoir, and a hydraulic pump station was set up to form a groundwater cascade development project together with the underground reservoir.

(2) Ecological environment control project. A flood discharge channel connecting the skylight of the upstream underground river with the entrance of the downstream underground flow is built in the flooded depression, and a flood discharge tunnel is excavated along the outlet direction of the underground river, so that the groundwater and surface water of the depression gushed from the skylight of the upstream underground river in rainy season are discharged from the outlet of the underground river in the eastern suburbs, and irrigation channels are introduced to irrigate the downstream ponds and cultivated land with an elevation of 825-830 m in Kedu Valley. The structure of the flood discharge project is designed according to the ground elevation of the flooded dam depression and the maximum "accumulated water" of the depression during the flood period. The drainage elevation is 840 ~ 835 m, and the slope is 5.6‰.

The project plan can be implemented by stages according to the local economic strength and urgency. The groundwater development and utilization project is the first phase and the ecological environment control and development project is the second phase.

4.4 Groundwater Development and Utilization Project (Phase I Project)

See Figure 7 for the layout of the first phase project, with a total investment of about 6,728,800 yuan.

(1) water storage project: ① underground reservoir. There is a gravity dam at the outlet of the underground river, with a dam height of 10m, a dam axis length of 25m and a dam crest elevation of 830m. The storage capacity of underground reservoir is 63× 104m3. ② Surface reservoir. The dam is located at 1.2km downstream of the exit of Jumu underground river, with a dam height of 3.5m, a dam axis length of 30m, a dam crest elevation of 8 14.0m, and a designed storage capacity of 10.5× 104m3. A reinforced concrete slab bridge with a width of 2.8m and a bearing capacity of 5t is set at the dam crest.

(2) Water diversion project. On the left and right sides of the underground reservoir dam, the south and north diversion canals are built respectively. The south main canal is 4.3km long and joins the south main canal of Tianshengqiao water diversion project at 6+600. The north main canal is 8km long, including 4 inverted siphon pipes, 700m long, 5 aqueducts, 400m long, 2 diversion tunnels, 440m long, main water supply pipe 100km, tap water φ150 mm.

Fig. 7 Plan of Jumu Underground River Development Phase I Project

(3) Water lifting project. The distribution elevation of villages in Kedu Town and Tangbian Town is 830 ~ 850 m, and the dam head of underground reservoir is equipped with three hydraulic pumps with a lift of 100m and a flow of 100 m3/h, 100 QJ 65438× 100 submersible pumps and/kloc-0.

4.5 Ecological Environment Control and Development Project (Phase II Project)

The section of the flood drainage channel is 3m×3m, and the length is1.2km; : The spillway tunnel has a cross section of 2.5m×2.5m and a length of 900m. The total investment of the project is about 365.438 billion yuan.

5 Main engineering geological conditions for the development of underground rivers

5. 1 Engineering conditions of underground reservoir

(1) dam stability. The regional earthquake intensity is less than ⅵ degree, and the regional crust is stable. According to the dam foundation exploration, there is no fault structure in the dam area, and the left abutment is bedrock mountain and the right abutment is hilly. The bedrock is thick layered limestone of the Permian Maokou Formation, and the saturated uniaxial compressive strength of the rock is 55.740~86.007MPa, which belongs to hard rock. Exploration only encountered a dissolution fracture at the depth of ZK8 hole above 20 m, which has been completely filled. The rock mass of dam foundation is integral and of good quality.

(2) Leakage in the dam area. The shallow surface of the dam site area has a high degree of karstification. The individual forms of karst are mainly dissolved fractures and dissolved pores, and vertical fractures in the northeast and southeast direction are mainly developed in the rock mass, with a development density of 3 ~ 6 /5m, which has good openness and strong connectivity. However, the karst degree in the deep underground is low, and there are only local dissolution cracks, so the rock mass is relatively complete (Figure 8). The water pressure test shows that the water absorption of rock mass is 0.004 ~ 0.07 L/min·m2, and the local water absorption is 0.1617 ~ 0.1984 L/min m2 (see table). Therefore, the dam foundation and abutment need to be embedded in fresh limestone to prevent leakage around the dam foundation and dam.

Fig. 8 Cross-sectional view of Jumu Underground River outlet dam site

Statistics of unit water absorption of drilling hole

(3) Leakage in the reservoir area. The elevation of the surface watershed between Jumu underground river basin and its adjacent underground rivers is 830m ~1165 m. According to the underground river tracing test, the mass concentration of Cl- at the outlet of Jumu underground river is 0.05538mg/L, and the water samples at the monitoring points of Burao underground river in the west and Xihe underground river in the east of the basin are 0.02769mg/L, which shows that rivers in different places are independent.

5.2 Engineering Geological Conditions of Surface Reservoir

There is no fault structure in the dam site area, and the dam foundation and abutment are thick layered limestone of Permian Maokou Formation, which belongs to hard rock. The rock mass of dam foundation is integral, with excellent quality and good stability. The cracks in the rock mass are undeveloped, mostly closed, and there are only local dissolution cracks, so the rock mass is relatively complete and the anti-seepage performance is generally good.

The surface reservoir area is Jumu Valley, which is the lowest drainage datum of local groundwater. Because the storage height of the reservoir is only 4m, the possibility of leakage in the adjacent valley of the reservoir area is small.

5.3 tunnel engineering conditions

Including drainage works and flood discharge tunnels. The strata in the tunnel area are all limestone of the Permian Maokou Formation, with no weak interlayer, good rock integrity, high mechanical strength, stable surrounding rock and good engineering properties. The diversion tunnel of canal system is higher than the groundwater level, so the possibility of water inrush is small. The water in the spillway tunnel of the flooded dam is lower than the groundwater level in the wet season and higher than the groundwater level 15 ~ 20m in the normal and dry season. Therefore, we should choose to construct in normal and dry seasons.

6 engineering advantages

By the end of 2005, the first phase of the project had been completed (photos 3 and 4).

Fig. 3 Ground Secondary Reservoir Project

6. 1 social benefit analysis

(1) Solve the drinking water problem of more than 6000 people and 10000 large livestock in Tangbian Town, Kedu Town, Pingtang County, end the long-term water shortage and unclean history of local people, and realize the national drinking water safety goal.

(2) To solve the irrigation water problem of 800hm2 farmland in the river basin and downstream drought and water shortage areas.

(3) Eliminate the karst flood disaster in floodplain and west mixed valley. Through land consolidation, about 67hm2 ~ 2 of land in flooded dam depression can be reclaimed, making full use of valuable land resources in karst areas.

(4) The combination of land resources development, poverty alleviation and rocky desertification control can solve the problem of ecological resettlement of more than 1.500 people (the current average population density is 78 people /km2) in the river basin and downstream rocky desertification areas, and create basic conditions for the survival and poverty alleviation of immigrants.

Photo 4 Underground River Reservoir Development Project

(5) In the 19.28km2 rocky desertification area after migration, it is possible to really close the mountain to facilitate afforestation, plant trees and return farmland to forests, so as to realize the restoration of rocky desertification ecological environment.

6.2 Economic Benefit Analysis

According to the information provided by Pingtang County Water Conservancy Bureau and Agriculture Bureau, the grain income will increase by1523,900 kg/a (calculated by increasing income by 2250kg per hectare per year) after 800hm2 of cultivated land below the underground river exit is guaranteed for irrigation. About 67hm2 ~ 2 of land in flooded dam depression can produce 2.7 million kg/a of grain, with a total increase of 4.2239 million kg/a in the whole region. According to the local grain market price of 2.40 yuan/kg, the economic income of agricultural production alone is 10 137400 yuan per year, which does not include other benefits brought about by the industrial structure adjustment driven by underground river development.

Therefore, the comprehensive benefits of the Jumu underground river development project are obvious, which is of great significance to the local social and economic development, the improvement of the ecological environment and the promotion of local people to get rid of poverty and become rich. At the same time, it can also explore an effective way to improve the ecological environment for karst rocky mountain areas with serious soil erosion.

7 conclusion

Underground river basin is rich in groundwater resources. The development of underground rivers not only promotes social and economic development, but also brings negative effects to the environment. In the past, some underground river development projects neglected the protection of karst environment, resulting in poor engineering benefits or even failure. Therefore, the development and utilization of groundwater must consider the hydrogeological and ecological environment characteristics of the whole underground river basin system as a whole, combine the development and utilization of groundwater with the ecological environment protection and governance of the basin and its adjacent areas, and make rational use of resources and environment in order to achieve twice the result with half the effort.

There are more than 1 130 underground rivers in karst mountainous areas of Guizhou province, and Jumu underground river is just one of these underground rivers. Its guiding ideology and engineering scheme of development and utilization can be used as an example of similar underground river development.

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Gao Morality, Zhang Shicong, et al. 1986. Study on karst in southern Guizhou. Guiyang: Guizhou People's Publishing House.

Guizhou Geological Engineering Survey Institute. 1989. research report on karst springs and underground rivers in Guizhou province, People's Republic of China (PRC).

Guizhou Institute of Technology. 1986. Evaluation and development of karst water resources in southern Dushan, Guizhou.

China geological survey. 2004. Feasibility Study Report of Jumu Underground River Karst Groundwater Development Project in Pingtang County, Guizhou Province

Wang. 2005. Study on Geo-model of rocky desertification control [J]. Guizhou Geology, 22 (2): 77 ~ 80