Brief introduction of poverty alleviation well drilling project in karst poverty-stricken counties in Guo Ding, Guangxi

Guangxi is an important part of karst area in southwest China, which is a world-famous karst area, with the best Guilin peak forest landform and Du 'an Dahua peak cluster landform in the world. At the same time, however, the distribution of water resources in karst mountainous areas is uneven in time and space, and a large number of villages are often seriously short of water in dry season, which can reach three to six months, and farmland is seasonally dry. 1997, the government of Guangxi Zhuang Autonomous Region began to fight against poverty and drought, and decided to first demonstrate water supply sources and drill wells for poverty alleviation in villages with more than 500 people in national poverty-stricken counties in the whole region (see figure 1).

Figure 1 Guangxi Zhuang Autonomous Region 1997 Distribution of Poverty Alleviation Wells in Poverty-stricken Counties

According to the arrangement of the government of the autonomous region and the Ministry of Land and Resources (formerly the Ministry of Geology and Mineral Resources), this work demonstrated the water supply sources of nearly 500 villages scattered in 28 national poverty-stricken counties in the whole region, and put forward suggestions for solving the drinking water for people and livestock by classification. With the approval of the autonomous region, 19 karst counties with well-drilling conditions 130 villages have carried out well-drilling for poverty alleviation. By adopting advanced geophysical exploration technology and popularizing multi-process air drilling technology, the drilling speed has been greatly improved. In the whole year, 207 wells were drilled, with a footage of about 20,000m, and 127 wells were completed, with a proven water volume of 54,392.1.6m3/d, which can solve the drinking water problem of 1.44 million people and 1.05438+0.75 million livestock.

This work pioneered the large-scale development and utilization of groundwater to solve the drinking water problem of people and animals in karst rocky mountainous areas in China. It shows that as long as scientific investigation and careful organization are carried out, the scheme of finding water in karst rocky mountain arid area can be successful. This is not only to solve the needs of farmland drought and drinking water for people and livestock in mountainous areas, but also to implement sustainable development. In the karst area of southwest China, it has great popularization significance.

2 The natural geological background and hydrogeological conditions of karst arid areas in Guangxi

2. 1 Meteorology and Hydrology

Guangxi is located in the low latitude zone, with the Tropic of Cancer running through the middle, and belongs to the subtropical maritime monsoon climate, with long summer and short winter, abundant rainfall, long sunshine, hot and rainy summer and autumn, occasionally extremely cold winter, and obvious dry and wet seasons.

The annual average temperature in this area is 17 ~ 22℃. The temperature changes gradually from north to south. The valley plain is higher than the adjacent hills and mountains. The temperatures in Chongzuo, Longzhou and Ningming in Zuojiang River Basin, Baise in Youjiang River Basin, and the coastal areas south of Pubei and Bobai are relatively high, with the annual average temperature above 22℃. The temperatures in Ziyuan, Jinxiu and leye county are relatively low, with an annual average temperature of 65438 07℃. The highest temperature is in July, and the average temperature in most areas is 27 ~ 29℃. The lowest temperature is in February and the average temperature from north to south is 5.5 ~ 15℃.

Most of the annual rainfall in Guangxi is in 1250 ~ 1750 mm, but it varies greatly among regions and is unevenly distributed. According to the rainfall intensity, it is clearly divided into six rainy areas and six rainy areas. Rainy areas are distributed in non-carbonate areas such as 90,000 Dashan to Yuechengling, Dayao Mountain, 100,000 Dashan, Daming Mountain, Yunkai Mountain and Rongda Mountain, with the annual maximum rainfall of 1.925 ~ 3.499 mm, while less rainy areas are mainly distributed in Gongcheng-Pingle, Laibin-Xiangzhou, Chongzuo-Fusui, Baise-Tiandong and Longjiang. The dry season is from 65438+February to the following February, and the rainfall only accounts for 6% ~ 15% of the annual rainfall.

The drought and flood disasters in Guangxi are very serious, and there is a trend of increasing gradually. According to the data of Southwest Resources Investigation Team of China Academy of Sciences, during the period of 1954 ~ 1986, the frequency of drought occurred very frequently, with the frequency reaching over 70% except Liuzhou, Guilin, Wuzhou and Beihai. Since the 1990s, the climate has increased abnormally and droughts have occurred frequently, which has brought great difficulties to the rural economy and people's lives in our region, especially in karst arid areas, and increased the sense of urgency in drought relief work.

The average natural runoff in Guangxi for many years is 65.438+0.88 billion m3, and the water yield modulus is 796,000 m3/a km2, ranking fifth in the national water yield and sixth in the water yield modulus.

River runoff in Guangxi mainly comes from atmospheric precipitation and belongs to rain source type. The general trend of annual runoff change is decreasing from coastal to inland. The average annual runoff depth is 795.7mm, with the maximum of 2400mm and the minimum of 300mm. The flood season of rivers accounts for 70% ~ 80% of the whole year, and the individual reaches of the left and right rivers account for 85% ~ 95%.

The main water systems are Xijiang (Pearl River) and Yangtze River. Xijiang River system is distributed in the south-central part of Guangxi, with tributaries such as Hongshui River, Yujiang River, Liujiang River, Gui Jiang River and Hejiang River, with a drainage area of 202,427km2, accounting for 84.7% of the total area of Guangxi, with an annual runoff depth of 75 1 mm and an annual runoff of153.87 billion m3, accounting for 8/kloc-of the total surface runoff in Guangxi.

The Yangtze River system is distributed in the northeast of Guangxi, with a drainage area of 8283 km2, accounting for 3.5% of Guangxi. In addition, there are several small rivers that enter the sea independently, with a total area of 2311km2, accounting for 10.2% of the total area, mainly distributed in Qinzhou-Fangcheng area.

The above-mentioned major rivers, especially in karst areas, pass through mountains, and the plain area along the river is not large, especially in poor areas of western Guangxi, where the population is scattered in peak-cluster depressions and peak-cluster valleys far away from rivers, which separates the rich surface water in these areas from population and land, which is not conducive to the development and utilization of surface water resources. This is also an important poverty-causing factor in poor areas of Guangxi.

2.2 Geological background and hydrogeological conditions

Karst poverty-stricken counties in Guangxi, mainly located in the central and western regions of the autonomous region, are also one of the most concentrated karst areas in China. Their landforms are characterized by karst peak-cluster depressions, peak-cluster valleys and karst peak-forest plains. They are located at the southern end of the Neocathaysian Third Uplift Zone in central and eastern China, and they are well-known exposed and semi-covered karst distribution areas. Geologically, it is located in Caledonian fold system and Yangtze paraplatform in South China. At the end of Caledonian, after Guangxi movement, most areas of Guangxi changed from geosyncline to paraplatform, which was connected with Yangtze platform, and formed paraplatform deposits dominated by carbonate rocks in shallow sea. Therefore, although the strata in China are completely exposed from the Upper Paleozoic to the Cenozoic, the Triassic carbonate rocks from the Upper Paleozoic to the Mesozoic are dominant, with a total thickness of more than 10,000 meters. The carbonate rocks have the characteristics of large-scale contiguous distribution and pure layer thickness, with a total area of 96,000 km2, accounting for about 4 1% of the total area. See table 1 for the main strata characteristics.

The carbonate rocks widely distributed in the region have formed the famous tropical karst landscape and unique karst hydrogeological conditions in Guangxi through internal and external geological processes, which have had an important impact on the development of karst water resources in Guangxi. Simply put, the distribution of karst groundwater in Guangxi has the following basic characteristics:

(1) The occurrence of groundwater is controlled by karst water-bearing strata. There are three types of karst water-bearing rock formations in Guangxi, among which limestone water-bearing rock formations are the most important and widely distributed, accounting for about 72% of the total area. Groundwater exists in karst caves and dissolved pipelines, which is rich but unevenly distributed. Dolomite water-bearing rock group, the distribution area accounts for about 6.0% of the total area, and groundwater exists in solution gaps, holes and caves, with good water abundance and relatively uniform distribution; The distribution area of impure limestone water-bearing rock group accounts for nearly 22% of the total area, and the occurrence of groundwater is between the two, but the water abundance is poor.

(2) The enrichment of groundwater is controlled by recharge conditions and geological structure. The larger the recharge range, the richer the groundwater; At the same time, geological structures such as folds and fault fracture zones often control the development of underground karst and become the main controlling factors of groundwater burial and migration.

(3) Groundwater depth is controlled by topography and erosion datum. In karst valleys and plains, the groundwater depth is shallow, generally 10 ~ 30 m, and it can reach 30 ~ 80 m or even deeper in peak-cluster depressions and valleys.

(4) Karst underground rivers and large springs are well developed. There are 435 underground rivers with a length of 2km and a low flow rate of 100 L/s, and 736 karst springs with a low flow rate greater than100L/s. The former has a total length greater than 10000km and an average distribution density of 0. 1 km/km2. But there are great differences in different regions, especially in western and southwestern Guangxi, where underground rivers are the most developed.

(5) The groundwater distribution is uneven. Because groundwater is stored in the cracks of karst caves, it is unevenly distributed on the plane or section, and often concentrated in a certain zone or section controlled by stratigraphic structure. The more developed the underground river, the more uneven the distribution of groundwater.

(6) The dynamic change of karst groundwater is great. In general karst canyons and plains, the annual variation of water level is about 10 ~ 30 m, and it can reach 30 ~ 50 m or even higher in peak-cluster depressions. Therefore, a large hydraulic gradient is often formed at the location where the terrain changes, which is a favorable location for building underground reservoirs.

Table 1 Summary of Major Lithostratigraphic Units in Guangxi

3. Deployment and effectiveness of poverty alleviation wells

According to the conditions of karst poverty-stricken areas in Guangxi and the determination of the people's government of the autonomous region to solve the drinking water problem of people and animals in villages with relatively concentrated population in poverty-stricken mountainous areas, we suggest to the leaders of the autonomous region that this work be carried out in two stages. In the first stage, that is, the preliminary demonstration stage, our bureau first organized a team to demonstrate the hydrogeology of water supply in water-deficient villages with an accuracy equivalent to 1∶ 10000. The water resources department is responsible for the construction of water diversion project, and those with water supply exploration conditions will be transferred to the second phase, and the well drilling project will be implemented by the Department of Geology and Mineral Resources, and the plan will be approved by the leaders of the autonomous region. In the three months from 65438 to the beginning of 0997, we organized nearly 50 hydrogeological investigation teams to demonstrate nearly 500 water-deficient villages provided by the Water Resources Department, and confirmed that more than 1/3 of them have water diversion conditions, 1/3 has well drilling conditions, and the rest 1/3 can only be realized by building water tanks.

From early April 1997 to drilling stage. In order to ensure the smooth implementation of this water-seeking poverty alleviation project, on the basis of primary selection, we further deployed 1 ∶ 1 10,000 geophysical prospecting methods in each village to further determine the water supply prospect and select the exploration target area. In this way, after geophysical exploration, 137 villages out of more than 60 primary villages are listed as poverty alleviation project villages, which are distributed in 19 karst poverty-stricken counties in central and western Guangxi, such as Nandan, Luocheng, Jingxi, Tiandeng, Debao, Lingyun, Jinxiu, Longzhou and Tiandong.

At first, many people held a wait-and-see attitude towards the success of drilling wells to find water in the popular karst mountainous areas. Because there are 1/3 villages identified as well-drilling villages, the hydrogeological conditions of water supply are very poor, or there is no water and no access, or the karst geological conditions are complex, and a few well-drilling teams have been in and out several times. In order to ensure the success of this demonstration well drilling project, the Bureau organized and set up a leading group headed by the Bureau leaders and attended by experts from various departments, and held a general mobilization meeting, requiring the participating units to send elite soldiers and strong experts with expert guidance, and requiring all units to ensure the close cooperation between hydrogeology and hydrogeology, adopt advanced and practical geophysical methods as far as possible, popularize advanced multi-process air drilling technology, realize high-efficiency and low-cost investment, and successfully complete this important task assigned by the autonomous region and the Ministry of Land and Resources.

In the past year, 10 has dispatched more than 50 drilling rigs, drilled 207 holes with a footage of more than 20,000 meters, completed 127 wells, and the proven water volume is 54,392.16m3/d, which is equivalent to a large water source. The water output of a single well is generally 10 ~ 100t/h, of which two wells have been built in the water source area of Huahong Village in Xincheng with the largest water output, with a total water output of 200m3/h. With the support of MSF, the most standard tap water plant in rural Guangxi has been built, which can solve 1 township and 4 villages.

Table 2 Distribution Statistics of Water Wells in Counties

In this well drilling project, 10 villages failed, the success rate of water exploration in the villages was 90%, and the completion rate of well drilling was nearly 60%. It should be said that it is not easy for karst mountainous areas with very complicated conditions. The direct result is to solve the drinking water problem of more than 65,438+people and nearly 65,438+10,000 livestock in 160 natural villages. More importantly, this work not only pioneered the large-scale development and utilization of groundwater to solve the drinking water problem of people and animals in karst rocky mountainous areas in China, but also solved a long-standing problem and debate, that is, whether the water search plan can be successful in karst water-deficient mountainous areas, the answer is yes. The key is to respect science and organize it carefully. From a deeper level, it has laid a good foundation for the sustainable development of karst poor mountainous areas. In poor karst mountainous areas, water conservancy infrastructure is very weak. Only by scientifically developing and utilizing local surface water and groundwater resources can we really take the first step to control drought and poverty.

4. Guiding ideology to solve the problem of drinking water for people and livestock in poor mountainous areas (improving water)

After the poverty alleviation work of drinking water for people and animals was carried out from 1997 to 1998 in Guangxi, the drinking water problem for people and animals in villages with relatively concentrated population in mountainous areas was basically solved or alleviated. Based on this work and the experience and lessons of previous water conservancy projects, we believe that in the future, drinking water for people and livestock in rural areas should be combined with the comprehensive drought resistance of farmland in water-deficient villages and villages, killing two birds with one stone and reducing the investment in drought resistance, because of the high degree of water supply guarantee of motor wells, it is often beyond the reach of other surface water sources; (2) Drinking water for people and livestock should advocate the policy of adapting to local conditions. The landform and hydrogeological conditions in poor karst mountainous areas are different, so the water supply mode should not be one-size-fits-all, and the choice of mode should be based on the principle of combining needs with possibilities; (3) On the basis of economic feasibility, if it is possible to drill wells, the intensity of drilling wells should be increased. This is because the southwest karst area is rich in atmospheric precipitation and has a high degree of water resources supply, but the degree of water resources development and utilization is still very low. At the same time, its water quality is good, which can generally meet the standard of drinking water source, which is also difficult to achieve in water storage projects; (4) Strengthen scientific argumentation, implement hierarchical guidance and reduce blindness. With the development of rural economy and the deepening of reform, we are increasingly required to adopt a scientific attitude towards drinking water for people and livestock (improving water) and adopt a policy of grading guidance for different situations. Therefore, we must spend a small amount of money first, do more preliminary argumentation, so that the later work can be based on a more scientific basis and reduce unnecessary waste.

5 conclusion

Southwest karst area is rich in rainfall and surface water resources, but the large-scale distribution of karst has created complex topography. The uneven distribution of precipitation in time and space separates water and soil resources from population settlements, which leads to serious drought and flood disasters in China and becomes one of the main factors of poverty in this area. Making full use of local groundwater resources and actively promoting exploration and drilling projects are important contents of local water conservancy work in the future and should be actively advocated. This is not only the need of local drought relief and poverty alleviation, but also the need of implementing the western development.