Effective development model of karst water resources in xiaojiang river basin of Luxi

(Yunnan Geological Survey Institute, Kunming 65005 1)

Fund project: large-scale land and resources survey project "Karst groundwater survey and demonstration of geological environment improvement in typical areas of Yunnan" (200310400024); Yunnan Science and Technology Plan Project "Study on Technical Scheme for Effective Development of Karst Water" (2003PY04).

Author: Wang Yu (1960—), male, professor-level senior engineer, mainly engaged in investigation and research of hydrology, engineering and environmental geology.

In order to guide the effective development of karst water resources according to local conditions and provide technical support for the comprehensive control of rocky desertification in karst mountainous areas, China Geological Survey chose Xiaojiang River Basin in Luxi to carry out demonstration research on karst water exploration and development. This paper summarizes some research results and experiences of this work. Under different karst eco-geological environment conditions, the main types of karst water sources, the occurrence characteristics of karst water and the development technical conditions are different. Therefore, according to different eco-geological environment divisions in the basin, karst water sources with typical significance are selected for karst water exploration and development experiments and demonstrations, and new technologies such as nuclear magnetic resonance and geological radar are carried out to find karst water. Nine demonstration projects of karst water development with different technical schemes were designed and constructed, and the technical schemes of karst groundwater exploration and development suitable for different karst eco-geological environments and water source types were summarized. Study and integrate the effective development model of karst water in karst basin, and popularize it in karst mountain areas to improve the development benefit of karst water and effectively control rocky desertification.

Key words: Xiaojiang river basin in Luxi; Types of karst water sources; Technical conditions for development; Exploration technology; Development engineering scheme

There are many karst basins in the karst rocky mountainous areas in southwest China, which have thousands to tens of thousands of hectares of cultivated land, and tens of thousands to millions of people live on karst plateaus or planation planes at all levels. The water surface of major rivers is much lower than that of major cultivated land distribution areas, densely populated areas and economic activity areas [1], resulting in the problem of "incompatibility between water and soil". Karst water storage system is like a natural reservoir in the upper reaches of a river. Scientific exploration, planning, development and dispatching will play a very important role in solving the problem of "incompatibility between water and soil" and alleviating the increasingly tense contradiction between supply and demand of water resources. Along the recharge, runoff and discharge process of karst water in karst basin [2], the eco-geological environment and main karst water source types have changed rapidly, and the characteristics of karst water occurrence and movement, exploration and development technical conditions and water supply demand have also changed [3]. Therefore, it is very necessary and urgent to study these changes, adopt different advanced and applicable technologies, deploy different experimental projects for karst water resources exploration and development, obtain effective technical schemes for karst water exploration and development suitable for different eco-geological environmental conditions and water source types through experimental research, integrate the effective development and utilization model of karst water in Xiaojiang River basin in western Shandong, popularize and apply it in the vast karst mountainous areas, improve the efficiency of karst water development and effectively prevent rocky desertification [4].

1 geographical survey

Luxi xiaojiang river basin is located in the east of Yunnan province, with east longitude103 30 ′ ~104 05 ′ and north latitude 2410 ′ ~ 24 45 ′, which belongs to the first-class tributary of Nanpanjiang river system. The main body is the luxi county area of Honghe Hani and Yi Autonomous Prefecture. The total basin area is 1009.28km2, and the karst area accounts for more than 70%. The middle and upper reaches of the basin are elliptic karst basins, and the long axis extends from northeast to southwest. The sedimentary flat dam area at the bottom of the basin is about 1700m above sea level, with an area of 78. 1km2, and the terrain is relatively flat. The elevation of karst mountain areas exposed around the basin is 1800 ~ 2459 m, and various karst forms are well developed; Xiaojiang basin downstream of the southern basin is the drainage benchmark of the basin, with the lowest point at 820m above sea level, V-shaped cross section and cutting depth of 500 ~1639 m. ..

It belongs to subtropical plateau monsoon climate, with mild climate, moderate rainfall and clear dry season and rainy season. There is a great difference in climate between mountainous areas and dam areas. The annual average temperature in this area is 15.2℃, the highest temperature is 36. 1℃, and the lowest temperature is -4.3℃. The annual average precipitation is 966.8mm, and the maximum is1251.5 mm. More than 80% of the precipitation is concentrated in June ~ 10. The average annual evaporation of water surface is between1204.1~1279.3 mm, the total length of Xiaojiang is 97.5km, the drop 100 1m, the flow rate is 0.52 ~ 39.83m3/s, and the annual average flow rate is 5.44. ..

The forest area of the basin is 269.38 square kilometers, with a coverage rate of 26.69%. The total area of rocky desertification is 265,438+065,438+0.75km2, accounting for 20.98% of the basin area, mainly distributed in the bare karst mountainous area of Xiaojiang Valley around Luxi Basin.

* * * There are 200,400 people in the river basin, including agricultural population174,300 people, accounting for 86.98% of the total population. In 2003, the GDP was 5079 1.72 million yuan, of which the agricultural output value accounted for 68.02%, the per capita grain was 39 1 kg, and the per capita net income of farmers was 1.426 yuan. The per capita net income of Tangsan Township, which is located in the karst high school and mountainous area, was only 688 yuan. The total area of cultivated land is 47,200 hm2, including 6540hm2 in paddy field and 40,600 hm2 in dry land, and the per capita cultivated land is about 0.24hm2. At present, the water shortage population is 510.7 million, and the cultivated land is short of water by 26 1 10,000 hm2.

2 Geological background

Xiaojiang basin belongs to the southeast Yunnan fold belt of South China fold system, and its structure is dominated by a series of NE-trending faults and folds. Yulong fault, Baishui syncline and Yangmeishan anticline are mainly developed. Structure controls the landform characteristics and the distribution of karst water in Xiaojiang river basin, and is the main controlling factor for the formation of underground river pipelines in Northeast China. Usually, spring points are exposed along faults, and bead depressions, sinkholes and caves are developed.

The exposed strata in Xiaojiang River Basin are mainly Mesozoic Triassic, Paleozoic Permian and Cenozoic Paleogene in some areas, and Cenozoic Quaternary in dam area, valley area and mountainous depression. Only mudstone, sand shale and siltstone of Xuanwei Formation (P2x) of Middle Permian are exposed in Paleozoic strata. Triassic in Mesozoic: sandstone and mudstone of Shangniaoge Formation (T3n) and Huobachong Formation (T3h), limestone and dolomite of Zhonggejiu Formation (T2g) and Falang Formation (T2f), with a small amount of thin argillaceous limestone and sandstone, and Feixianguan Formation (T 1f) and Yongningzhen Formation (T65438+). The Neogene Rumeiyi Formation (E 1l) is a conglomerate; Quaternary (Q) of Cenozoic is red clay, sandy clay, fine sand and gravel. Limestone and dolomite of Gejiu Formation (T2g) are the most widely distributed strata in the basin.

3 karst eco-geological environment and hydrogeological characteristics

The types of karst eco-geological environment in Xiaojiang River Basin are complex and diverse, from karst water recharge area to drainage area, passing through different types of karst morphological combination units such as karst mountain, karst valley, karst hill, peak-cluster canyon, karst flat dam and karst valley (Figure 1).

Karst mountainous area is characterized by steep hillside, cool climate, exposed bedrock, shallow soil layer, scattered distribution and poor soil, mostly suitable for forest areas, mostly dry land, mainly dry farming, mainly planting corn, buckwheat, potatoes and other crops. The transportation is inconvenient, the villages and towns are small in scale and scattered in residence. Surface karst depressions and valleys are developed, funnels and sinkholes are densely distributed, and precipitation leakage is serious. It is the main recharge area of karst water, and the conditions for building reservoirs are extremely poor, and water resources are seriously scarce. The development of underground karst is extremely uneven, and the karst saturated zone is buried deeply. The water diversion and storage space is mainly tunnel pipe, and karst water mainly flows through caves. There are many funnels and sinkholes along the underground river to communicate with it, and karst water is mainly replenished through these channels. The storage capacity of karst water system is weak, and the water level and discharge change dramatically in seasons. A large part of karst water is discharged at the bottom edge of the basin in the form of large springs and underground rivers. It is very difficult to develop karst water in saturated zone, resulting in zonal water shortage. Rural domestic water and drought-resistant seedling protection water are in short supply. However, the exposed position of surface spring water in karst mountain area is higher, the water quality is better, and the development technology is less difficult. The amount of water can basically meet the needs of rural life and drought resistance and seedling protection in karst mountainous areas. Therefore, it has important water supply significance and development value in the deep karst mountainous area of saturated zone.

Figure 1 Summary of Hydrogeological Structure of Xiaojiang River Basin in Luxi

1-loose soil cover; Two-sided karst zone; 3- Karst fissure; 4- Water-conducting karst cave pipeline; 5- Karst lifting spring; 6— the flow direction of karst water; 7-Karst sinkhole; 8— Surface rivers and water levels; 9— Surface rivers and their flow direction; 10- elevation point

Karst canyons, karst hills and peak-cluster depressions are mainly distributed between the mountainous areas around the basin and the flat dams at the bottom of the basin, with mild climate, small relief, low vegetation coverage, developed depressions and valleys, broken terrain, thin soil layer, poor soil fertility, strong soil erosion, serious rocky desertification and poor irrigation conditions. Dryland is the main area, followed by paddy fields, and corn, buckwheat, potato, rice, cash crops and fruit are mainly planted. Convenient transportation, dense population and dense villages and towns. Surface sinkholes, dissolved wells, depressions and dissolved troughs are developed, reservoir leakage is strong, underground karst is uneven, karst saturated zone is buried deeply, and cave crevices form water diversion and storage space. Karst water coexists with karst cave pipe flow and dissolved diffusion flow, and there are many spring points in valleys and depressions, but the flow rate changes greatly. Serious surface water leakage, uneven distribution of karst water and low completion rate have caused water shortage in such areas [5]. It leads to difficulties in rural domestic water use, development of breeding and courtyard economy, seedling protection and drought resistance, large-scale management of famous fruit forests in karst rocky mountainous areas and ecological environment construction. It is suitable to solve the problem of rural domestic and production water use to develop the hidden karst water in vadose zone and the water-rich land in the ground strap.

Pingba has flat terrain, mild climate, deep soil layer, fertile soil, flat land, abundant water resources, good irrigation conditions and convenient transportation, which is most suitable for industrial and agricultural production and urban construction. Therefore, it is a traditional main agricultural producing area with dense population, large town scale, dense distribution, many factories and developed agricultural production. This has also caused serious pollution of surface water and shallow pore water. Sampling and laboratory analysis in Daxing Bao area showed that nitrite exceeded the standard by 2925 times, ammonia nitrogen exceeded the standard by 30 19 times, bacteria exceeded the standard by 75 times, and Escherichia coli exceeded the standard by 800 times, resulting in serious water shortage, which led to difficulties in rural domestic water use, and drought and water shortage in dry land around karst platform area was also very serious. Karst water in this area mainly comes from the lateral runoff in the surrounding bare karst mountainous areas, and a small amount of atmospheric precipitation is replenished through the vertical infiltration of pores in loose overburden. In lateral runoff, a part of karst water from the upper runoff zone above the bottom of the basin forms large springs and underground rivers along the edge of the basin on the basis of the bottom of the basin. Karst water in the lower runoff zone below the basin bottom continues to spread to the downstream of the basin in a nearly horizontal two-dimensional solution gap, and then flows through the sinkholes and caves existing in the south of the basin to be collected and discharged into Xiaojiang Canyon. Daxing Bao area is a transition zone where karst water changes from shallow to deep, from relatively uniform horizontal two-dimensional fissure diffusion to uneven three-dimensional karst cave pipeline flow. The buried depth of karst water gradually increases, and the runoff gradually concentrates. Karst water is collected in this area, and the covered karst aquifer group has huge adjustable water storage resources, allowing large exploitation and relatively uniform karst development. It is the main division of general water supply drilling and development, and is suitable for the joint planning and development of large springs or underground rivers and water-rich blocks to effectively regulate, develop and utilize karst water.

Karst Canyon in South China has steep vertical slope, deep terrain cutting, steep valley slope, developed valleys, low vegetation coverage, shallow soil layer and scattered land, mainly sloping land. A variety of wheat and corn are planted in the upstream, and citrus and bamboo are planted in the downstream, which leads to strong soil erosion and serious rocky desertification. The traffic is extremely poor, the population is sparse and the villages are sparse. The surface runoff above the valley slope is very fast, the karst water is buried deeply and the spatial distribution is extremely uneven. The pipe flow of karst caves is the mainstream, and it is concentrated at the bottom of the valley, so water resources are in short supply. Developing surface spring water to solve the difficulty of rural domestic water use. Xiaojiang river basin is a centralized drainage area of surface water and groundwater in the whole basin, which is rich in hydropower resources, but poor in natural resources and environmental conditions such as land. Therefore, it is appropriate to build small and medium-sized hydropower stations to develop hydropower resources.

Karst water in Xiaojiang basin is infiltrated by atmospheric precipitation, and its upstream runoff is based on the bottom of Luxi basin, discharged in the form of spring water and underground river, converted into surface water, and finally collected in the south of the basin, and discharged into Xiaojiang through workers and peasants tunnels and tiankeng. The downstream runoff is discharged by deep runoff based on the water surface of Xiaojiang River (Figure 1). The annual average recharge of karst water in the basin minus the upstream runoff based on Luxi basin, the loss after the development and utilization of karst water in Xiaojiang He basin should be equal to the downstream runoff of karst water in Xiaojiang basin.

Balance equation of karst water in river basin;

QR-Q 1-Q2=QD-Q3

Among them:

QR—— natural recharge of karst water in Xiaojiang River Basin (ten thousand m3/a);

QD—— discharge of karst water in Xiaojiang River Basin (ten thousand m3/a);

Q 1—— Based on the upstream runoff at the bottom of Luxi Basin (ten thousand m3/a);

Q2—— the loss after the development and utilization of karst water in Xiaojiang River Basin (ten thousand m3/a);

Q3—— Surface water discharge of tiankeng and drainage tunnel at the southern end of Luxi karst basin (ten thousand m3/a).

QR is calculated by infiltration method, the recharge area is the bare karst area of the whole basin, and the rainfall is the rainfall of luxi county Meteorological Station in 2003. Q 1 The method of summing up spring flow and underground river flow is adopted, that is, all natural dew point flows (measured flows) in the catchment area of karst basin in western Shandong are accumulated during the field investigation in 2003; Q2 is the total exploitation amount of the whole basin minus the water intake, and the calculation formula is Q2 = QK (1-tS), where QK is the exploitation amount of karst water in Xiaojiang Basin in 2003, and TS is the water intake coefficient, which is 0.85 according to the regional experience; Q3 is the displacement of workers and peasants tunnel and sinkhole at the southern end of the basin in 2003; QD is an unknown number.

The year of 2003 is chosen as the balance year. Through calculation, the recharge of karst water in Xiaojiang River Basin in 2003 is1401312000 m3/a, the upstream runoff is 69 178900 m3/a, and the downstream runoff is 6/kloc-0. This paper quantitatively explains the resource prospect and potential of karst water development in karst basin for the first time.

Table 1 Calculation Results of Karst Water Balance in Xiaojiang River Basin of Luxi (unit: 10,000 m3/a)

From the spatial distribution, the karst water in the karst mountain areas around Luxi basin is of good quality, mostly good and good, and most of them are suitable for drinking. The karst dam area covered at the bottom of Luxi basin is mainly good in water quality, and a small part is good, which is suitable for drinking and industrial and agricultural water. The water quality of Xiaojiang bare karst valley is poor, mainly because a large amount of surface water is converted into groundwater, which is seriously polluted and most karst water is not suitable for drinking. It reflects the process of pollutants gradually gathering downstream under the dissolution and transportation of karst water.

4 Karst water source types and development technical conditions

According to the geological factors that affect the selection and design of karst water exploration and development technical scheme, that is, the development technical conditions, the natural dew point or hidden water-rich blocks of karst water that can meet the general production and domestic water supply requirements in the basin are classified and evaluated. Firstly, according to the buried distribution of karst aquifer and the exposed state of karst water, karst water sources are divided into natural exposed karst water sources and concealed karst water sources [6]. Then, according to the spatial form, structure and hydrodynamic characteristics of karst water-bearing media, the naturally exposed karst water sources are further divided into three subcategories: underground rivers, springs and surface springs. Hidden karst water sources are divided into two sub-categories: saturated zone water-rich areas and surface water-rich areas (Table 2).

Table 2 Classification Statistics of Karst Water Sources

The exploration and evaluation of natural exposed karst water sources should adopt geological mapping, observation and testing, and the exploration and evaluation of concealed karst water sources should adopt geophysical exploration, drilling, geological analysis, observation and testing. Among the naturally exposed karst water sources, underground river water sources mainly include Arugudong underground river, Maoshuidong underground river, Yongning underground river and Xiazhai underground river, most of which are distributed in karst canyon area, and the flow rate is generally 100 ~ 1400 L/s, which can be used as the main water sources for production and living, ecological construction and energy development, and is suitable for impounding and building reservoirs at the outlet or downstream. Spring water sources mainly include Pijiazhai spring and Arufa spring. , mostly distributed in basin margins and karst canyons. The flow rate is generally 20 ~ 1200 L/s, which is the main water source for production and domestic water and ecological construction water. It is suitable for drainage or pumping water by adjusting backwater with beam flow at the outlet. The water sources of surface springs mainly include semi-porous surface springs in the Gulf and surface springs in Li Ziqing, which are mostly distributed in karst mountainous areas, karst canyons, karst hills, peak-cluster depressions and basin-bottom marginal platforms, and the flow rate is generally 0.5 ~ 15l/s, but the dry season and rainy season change greatly, and there are many interruptions in the dry season. It is the main water source for dispersing rural domestic water and developing famous economic crops in karst mountain areas. Among the hidden karst water sources, there are two water-rich blocks, Luxi and Baishui, which are saturated, with an area of about 70km2, which is of the greatest significance for centralized water supply in cities, villages and towns, factories and mines, and is suitable for deep well mining. The water-rich blocks in the surface area mainly include Nabao water-rich blocks and good water-rich blocks, with an area of about 3km2, which is of the greatest significance to the water supply of rural courtyards in higher positions and is suitable for shallow well mining.

According to the evaluation of water source types, all underground rivers are polluted to some extent, and the water quality is poor, and the water quality has basically not changed in dry season and rainy season; The quality of karst spring water is mainly good, and some are excellent and poor; The quality of surface spring water is poor-extremely poor; The water quality of water-rich blocks in saturated zone is mainly excellent-good, and some aquifers in the lower reaches of the basin are slightly polluted and the water quality is poor. The water quality of water-rich blocks in the surface area is generally poor.

5 technical scheme of karst water detection

The karst development in the basin is uneven in plane and vertical direction, and the water abundance is very different, so it is very difficult to find water. The completion rate of drilling in Daxing Bao area in the south of the bottom of the basin is only about 20%. Generally, the water inflow of a single well is tens of cubic meters/day, but the maximum water inflow can exceed1000 m3/d. In this study, the most advanced geophysical exploration technology is adopted and effective method combination experiments are carried out. Seven demonstration sites with water-rich blocks in saturated zone and surface water-rich blocks, naturally exposed karst springs and * * * distributed in different eco-geological environment conditions were selected to carry out the work, to study the technical effectiveness of geophysical exploration methods, to obtain technical experience and related parameters, and to integrate effective exploration technical schemes. Seven methods, such as apparent resistivity sounding, induced polarization sounding, nuclear magnetic resonance, transient electromagnetic method, joint profile method, geological radar and high density electrical method, are mainly selected.

5. 1 Hidden karst water source

5. 1. 1 saturated zone water-rich area

The apparent resistivity (ρs) curves of electrical sounding are mainly A-type, but also KHA-type and HA-type. The karst water-bearing section of each borehole shows a low resistance zone with ρs value of100 ~ 500 Ω m, and the single curve corresponding to the detection point has obvious gentle section. The vertical bedding of karst changes greatly. Dayi village is located at the bottom of karst trough valley in the upper reaches of the basin. There are four karst development sections with distribution depths of 7.9~9.0m, 18 ~ 30m, 40 ~ 60m and 130 ~ 65438+40~60m respectively. There are two karst development sections in the three villages downstream of the flat dam area at the basin bottom, with the distribution depths of 8.9~20m and 100 ~ 150m respectively. The ρs profile curve of electrical sounding reflects the lateral change of karst. For example, the intensity of karst development in Dayi Village is moderate, and the ratio of long axis to short axis of ρs polar diagram of annular sounding is 1. 1 ~ 1.3, which shows that karst development is relatively uniform on the plane. The karst in the three villages is basically moderately developed and locally strongly developed. The ratio of long axis to short axis of ρs polar diagram of annular sounding is 2.2 ~ 4.0, which indicates that the anisotropy is obvious and the karst development is mainly controlled by Sancun fault.

The nuclear magnetic resonance * * * vibration method was first applied to karst water detection in Yunnan, and 15 points were arranged in four demonstration sites. Within the effective detection depth, its electrical stratification can reflect the layered structure characteristics of karst aquifer and its relative water abundance. The buried depth, water content and porosity of the aquifer at the proposed hole location of 100m are basically found out, which is basically consistent with the drilling results. It is found that the relaxation time of NMR signals corresponding to the main karst water-bearing profiles in the basin is generally in the range of 100 ~ 200ms, and the water content is 1.4% ~ 6%. For example, there are three aquifers at the point of 10,000 mu orchard/kloc-0, which are located at 1 5 ~ 27m, 27 ~ 40m and 62 respectively. Drilling reveals that 5 ~ 3 1m is the first aquifer, which is filled with dissolved clay, with weak water-abundance, corresponding to the first layer of NMR, with relaxation time of 19 1ms and water content of 2.7%. The second layer is 3 1 ~ 65m, with relatively complete rocks and weak water-abundance, corresponding to the second aquifer of NMR, with relaxation time of 640ms and water content of 1. 1%. The third layer is 65 ~ 200 m, with well-developed dissolved pores and medium water abundance, which is the main aquifer, corresponding to the third aquifer of NMR, with relaxation time 157ms and water content of 5.9%.

The experiment adopts the scheme of combining multiple methods. Firstly, the apparent resistivity sounding is used to control the area, and the water-rich area is initially determined. According to the results of geological survey and electrical sounding, several alternative hole locations are selected comprehensively. Then, around the candidate hole position, the relative water-rich degree of the silo surrounded by each 75m×75m square antenna is determined by nuclear magnetic resonance detection, and the most water-rich silo is selected. Finally, in the most water-rich silo, the specific burial distribution position of karst water storage gap is determined by IP sounding of 10m or densified apparent resistivity sounding. This scheme greatly improves the well location accuracy, and the completion rate of five deep wells is 100%.

5. 1.2 Surface water-rich block

Surface karst water is widely distributed in the survey area, but the distribution is uneven. In order to detect the development of surface karst and provide basis for the layout of courtyard shallow water supply wells, 66 geological radar profiles were laid in Nabao Village. The measurement results show that the Quaternary overburden has the characteristics of strong energy, high frequency and good continuity, with a thickness of 2 ~ 6 m and a time window of 0 ~ 100 ns. The second layer is Triassic weathered limestone with weak energy, great variation, low frequency and poor continuity, with a thickness of 8 ~ 16m and a time window of 50 ~ 300 ns. There is a "dead zone" downward, and there is no obvious reflection or random reflection, indicating that it has entered the bedrock. When water-rich karst develops, strong reflection waves can be formed. Through geological radar detection, three abnormal points were selected for pilot hole construction, all of which were successful. The results show that GPR has high accuracy in detecting lithologic stratification and karst fracture zone with shallow buried depth less than 30m.

5.2 Natural bare karst water source

Pijiazhai Daquan is selected as a demonstration site, and a 12 high-density resistivity profile with a total length of 7995 meters is arranged. There are 6 GPR profiles, with a total length of 370 meters and 3 electrical sounding points/kloc-0. The results of high-density resistivity measurement show that the south of Pijiazhai spring point 18 line is the boundary, and the difference between north and south is obvious. The apparent resistivity profile in the south is layered, and the electrical layer structure is stable. The downstream side of the spring mouth is a high-resistance uplift, which indicates that the karst is undeveloped and has become an underground dam, which is the premise of the backwater project. The apparent resistivity profile in the north has a large lateral change, and the high and low resistances are alternately arranged, indicating that the structure of the electrical layer is complex and unstable, and the karst is relatively developed. The spring point is multi-channel water, which can be roughly divided into three in the north-south direction and one in the northwest direction. Except for the east side 1, the other three lines are all gathered at the spring point, and the buried depth of the pipeline near the spring mouth is about 10 ~ 20m. According to the drilling verification, the estimated surface clay layer thickness is close to the actual situation, and all the inferred karst development zones have been drilled into waterways.

For naturally exposed karst water sources, when the detection depth is less than 60m, the high-density resistivity method can provide a direct and high-resolution two-dimensional geoelectric profile. Electrical sounding and ground penetrating radar can be used for verification in abnormal areas, which can provide more accurate karst distribution position and buried depth.

6 Karst water development project plan

According to different eco-geological environment conditions, 9 demonstration projects for exploration and development of different types of karst water sources have been deployed (Figure 2).

Fig. 2 Layout plan of demonstration project for effective exploration and development of karst water in Xiaojiang River Basin, Luxi.

1- deep tube well development demonstration site; 2- Demonstration site of pressure regulating backwater development of karst spring beam; 3- Shallow tube well development demonstration site; 4- Demonstration sites for storage and development of surface spring water; 5- Bottom boundary of the basin; 6- water body; 7- watershed boundary

In the karst mountain karst water supply area around the basin, two demonstration projects, namely, semi-porous surface spring water storage in the bay and surface spring water storage in Li, were arranged. In the upper reaches of the river basin, in the geosyncline valleys and peak-cluster depressions of the karst terraces, in the upper reaches of the underground river system, in Dai Yi Village and Wanmu fruit forest in the uneven karst water recharge-runoff area of the river basin, two demonstration projects for deep well development in exposed water-rich blocks with saturated zones have been deployed; 1 Pijiazhai karst spring backwater development demonstration project is deployed in the karst water basin belt at the upper part of karst piedmont valley at the upper reaches of the basin. 1 shallow well development and demonstration project of courtyard tap water supply in surface water-rich block were deployed in Nabao village, karst water supply runoff area of karst hilly platform in the middle and lower reaches of the basin. Two demonstration projects for deep well development in water-rich blocks covered with vadose zones were deployed in Sanxin Village in karst water runoff area and Daxing Fort near runoff transition zone. 1 Deep well development demonstration project in water-rich block in buried saturated zone is deployed in the east of Dinghe Village, flat dam area at the basin bottom. Seven cascade hydropower stations have been built on Xiaojiang River, with a total installed capacity of 35380kW.

These demonstration projects embody the principles of adapting to local conditions, taking water for many times and comprehensive utilization [7], and have achieved remarkable economic, social and environmental benefits (Table 3).

Table 3 Statistical Table of Achievements of Karst Groundwater Development Demonstration Project in Xiaojiang River Basin of Luxi

After demonstration and summary, the effective development mode of karst water in karst basin is obtained (Figure 3). That is, along the whole process of karst water circulation in the basin, the combination of conventional technology and advanced technology is applied to find out the enrichment law, water source type, development technical conditions and karst water resources in the process of karst water recharge, runoff, discharge and intermediate transformation; In order to adapt to the eco-geological environment and its changes, according to the main karst water source types, karst water occurrence characteristics and development technical conditions in different karst eco-geological environment areas of the basin, combined with the characteristics of water demand, karst water development projects are planned and deployed. In the bare karst mountain recharge area around the basin, surface spring water and spring water storage and diversion projects are mainly arranged; In the karst valleys, peak-cluster depressions and karst platform areas around the basin bottom, underground rivers and hidden springs are mainly arranged for diversion, lifting and plugging, and the saturated zone and water-rich blocks of the ground strap are mined in combination with sinking; In the sedimentary flat dam area at the bottom of the basin, the water-rich block in the saturated zone mainly adopts sinking mining, combined with underground river and spring flow, lifting and plugging; In the valley area of the lower reaches of the river basin, it is mainly to build cascade dams and reservoirs, build cascade power stations and develop rich hydraulic resources [8].

Fig. 3 Effective development model of karst water in karst basin

1-loose overburden; Two-sided karst zone; 3- Karst fissure; 4- Water-conducting karst cave pipeline; Five rivers; 6- Surface spring storage project; 7- Daquan backwater drainage project; 8— Deep well engineering in water-rich block in saturated zone; 9— Shallow well project in water-rich block in surface zone; 10- cascade hydropower station project

7 conclusion

The effective development model of karst water in Xiaojiang river basin in Luxi fully embodies the characteristics of adapting to local conditions, multi-source and multi-way water intake, and has achieved the predetermined demonstration goal and achieved remarkable economic, social and environmental benefits. In 2005, Yunnan suffered the worst spring drought in 25 years. However, the demonstration projects are running normally and the drought resistance effect is very remarkable. Many news media have reported and praised: "The drought is serious, and geological science and technology have brought' seedling protection water' to Yunnan".

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