Main conclusions

The Yumen-Zhen Shi, Anxi-Dunhuang and Huahai basins in the 1) basin are subsidence basins since the Cenozoic era, with extremely thick terrigenous semi-cemented-loose piedmont facies and fluvial-lacustrine facies deposited. The boundaries of all basins are controlled by regional faults and tectonic uplift, and the bottom boundary is dominated by Pliocene (N2)- Lower Pleistocene (Qp 1) strata.

2) The main aquifers in the study area are mainly composed of pore phreatic water of middle-upper Pleistocene, confined water aquifer and Holocene pore phreatic water aquifer, which are distributed in alluvial and lacustrine strata of each basin. The lithology of aquifer is alluvial gravel, gravel, sand and lake sand, clayey silt and loam. In addition, there is underground fresh water in the Pliocene-Lower Pleistocene glutenite in Yumen Town, which is rich in water and good in water quality, and has the significance of water supply.

3) Affected by climate drought and human activities, the groundwater level in Shule River basin has shown a regional downward trend in recent 50 years, with a larger decline in Yumen-Zhen Shi Basin in the south, a smaller decline in Huahai Basin and Anxi-Dunhuang Basin in the north, and a smaller decline from the piedmont to the north and south basins in the fine soil plain. At the end of 2002, the water level at the top of the alluvial fan in Changma decreased obviously, while the water level in some receiving areas in Changma, Shuangta and Huahai irrigation areas increased. Due to the over-exploitation of groundwater in Danghe irrigation area, the water level is declining, and the crescent spring is also threatened. The spring resources at the front of alluvial fan in Changma are decreasing year by year, from 244.7 million m3 in 1977 to 654.38+568 million m3 in 2004, with a decrease of 87.9 million m3, and the spring brain generally moves down.

4) Groundwater is mainly distributed in Shule River and Danghe River dry delta. Various forms of leakage in Gobi area are the main source of river water after it comes out of the mountain. Among them, the leakage of water from rivers, canals and fields is very large, accounting for 56.5% ~ 93.2% of the total recharge. The consumption of groundwater depends on the overflow and evaporation of spring water in oasis plain. Groundwater in each basin is mainly formed by evaporation and enrichment on the basis of surface water. There is evidence that the formation age of groundwater in the lower reaches of lacustrine plain is relatively old, which accords with the hydrogeological characteristics of slow groundwater flow and slow water circulation in this area. At the same time, the study shows that the runoff alternation of the lower confined water is relatively slower than that of the upper diving.

5) The groundwater system in the basin is divided into three zones. The first division represents the whole groundwater circulation system in Shule River Basin. According to the recharge, diameter and discharge characteristics of groundwater, it is divided into three secondary areas. According to the boundary characteristics of landforms and geological structures, the secondary zoning is divided into five tertiary zoning. According to the lithologic structure characteristics of aquifer, the third-level division is divided into six groundwater subsystems. Through the analysis of drilling data, it is determined to be a single-layer diving subsystem and a multi-layer diving-confined water subsystem in the longitudinal direction.

6) The groundwater chemical field in Shule River Basin shows the horizontal and vertical zoning evolution law, which can be divided into fresh water area, fresh water-salt water covered area and salt water area from upstream to downstream. Freshwater is distributed in most alluvial fans of Shule River and Yulin River in the south of Yumen-Zhen Shi Basin in the middle reaches, most alluvial fans of Danghe River in Anxi-Dunhuang Basin in the lower reaches and the delta zone in the east of Anxi Basin, which is roughly consistent with the distribution of single phreatic zone. TDS of groundwater is less than 1g/L, and the main hydrochemical type is bicarbonate-sulfate.

Brackish water is distributed in the vast fine soil plain in the north and south basins, and the hydrochemical types are generally HCO3-SO4-Mg-Na, SO4-HCO3-Mg-Na and SO4-Cl-Mg-Na. The salt zone in the basin only occurs in the ancient lake area, and the hydrochemical types are Cl-Na-Ca, Cl-SO4-Na and SO4-Cl-Na-Mg, and the TDS is generally greater than 5g/L. ..

7) The groundwater in the piedmont Gobi zone (especially in the piedmont of Dahe Mountain) in the middle reaches of the basin is active and alternating, so that the aquifer skeleton is always in a state of leaching, and the soluble salt content is extremely low, forming an insoluble and stable geochemical background, with a low degree of groundwater salinization and a slow rise of TDS. From the piedmont Gobi to the fan-edge overflow zone, horizontal runoff is dominant, and the groundwater continuously eluviates the medium along the way, and the ion concentration in the water increases, and the TDS gradually increases. In the fine soil plain area downstream of the overflow zone, the groundwater runoff is relatively slow and the water level is shallow. Surface phreatic water is mainly vertical alternation, with obvious evaporation and transpiration. The groundwater runoff in the downstream basin is very slow, the evaporation and concentration of surface water are absolutely dominant, the TDS of groundwater is very high, and even brine is formed.

8) The total amount of natural groundwater recharge resources is 955,800,400 m3. According to the watershed, Yumen-Zhen Shi watershed is 493,465,438+900,000 m3, Anxi-Dunhuang watershed is 383,565,438+760,000 m3, and Huahai watershed is 80,727,900 m3. In terms of counties and cities, Yumen City has 3.2 million100800 m3, Anxi County has 5 million14669800 m3 and Dunhuang City has 22 million1969700 m3.

Under the condition of P=50%, the exploitable groundwater resource is 300,585,300 m3. Seen from the basin, the exploitable groundwater resources in Yumen-Zhen Shi, Anxi-Dunhuang and Huahai basins are129.3564 million m3, 140 10.37 million m3 and 3 165438 respectively. By county, Yumen City, Anxi County and Dunhuang City are113,356,400 m3,153,294,400 m3 and 45,662,500 m3 respectively.

Groundwater reserves are 520.328 billion m3, including fresh water reserves of 47 1.75 billion m3, brackish water reserves of 45.954 billion m3 and brackish water-salt water reserves of 2.624 billion m3. In terms of river basin, Huahai River Basin is the smallest, accounting for 62.696 billion m3; Yumen-Zhen Shi basin is relatively large, accounting for1284.3 million m3, and Anxi-Dunhuang basin is the largest, accounting for 329.203 billion m3. In terms of counties (cities), Yumen City is the smallest, accounting for 86.867 billion m3, Anxi County is the largest, accounting for1303.09 billion m3, and Dunhuang City is the largest, accounting for 303 153 billion m3.

9) According to the Groundwater Quality Standard (GB/T 14848-93), the phreatic water quality in the middle and upper parts of alluvial fans in each basin is good-good, and the phreatic water quality in the fine soil plain at the front of alluvial fans is poor-very poor. Except for Ganhaizi, Tangyihu, West Lake and Yumenguan West, the water pressure quality in most areas in the basin is good-excellent.

10) The groundwater potential coefficients of Yumen-Zhen Shi, Anxi-Dunhuang and Huahai basins are 3. 16, 1.5 1 and 5.66, respectively, and the groundwater potential is relatively large. The groundwater potential in Anxi-Dunhuang basin is mainly concentrated in Shuangta irrigation area and peripheral development zones.

1 1) The middle and upper alluvial fans and the central and southern irrigation areas in each basin are regions with strong sustainability; The middle and lower parts of Yulin diluvial fan, the northern and western parts of Shule River Delta in Anxi-Dunhuang Basin, the central and western parts of Danghe diluvial fan, the periphery of Huahai Irrigation Area and the piedmont diluvial fan area in Guan Dan are the regions with strong sustainability. Most of Changma irrigation area in Yumen-Zhen Shi basin in the middle reaches, fine soil zone in front of Yulin alluvial fan, barren area in the west of Shuangta irrigation area in Anxi-Dunhuang basin in the lower reaches, Danghe irrigation area, middle and lower part of Danghe alluvial fan, lower part of alluvial slope in front of Karatashi mountain, Youhe alluvial fan in Huahai basin, Qingshan farm and middle and east of the basin are sustainable general areas. The weak areas are the middle reaches of Rabbit Hulu-Ziqiao Nature Reserve in Yumen-Zhen Shi Basin, the lower reaches of Lucaogou, the West Lake Irrigation Area and the lower reaches of Tangyi Lake in Anxi-Dunhuang Basin, the periphery and north of Xihoukeng to Wanyao Nature Reserve in Yumen Gate, the northern nature reserve in Huahai Basin and the middle and east of well irrigation area. The ancient channel of Shule River in the downstream basin, Houkeng to Wanyao Nature Reserve in the west of Yumenguan, and the east of well irrigation area in Huahai basin are weak areas of sustainability.

12) By the end of 2004, there were 3,382 motor wells in the middle and lower reaches of Shule River, with a total exploitation of groundwater168.7 million m3, of which Anxi-Dunhuang Basin was the largest, accounting for 63.78% of the total exploitation, with 2,384 wells. Yumen-Zhen Shi basin is the second, accounting for 49.9 million m3, accounting for 29.75%, and the number of production wells is 792. Huahai Basin is the smallest, only165438+200,000m3, accounting for 6.65%, with 206 wells.

13) The areas with good environmental quality are Changma, Danghe and Shuangta irrigation areas, all of which are large irrigation areas. The areas with general environmental quality are Yulin irrigation area, Huahai irrigation area and Huahai barren area. The areas with poor environmental quality are mainly the wasteland west of Yumenguan and the wasteland north of Huangdunzi in Anxi-Dunhuang Basin. To sum up, the quality of geological environment in this area has the following laws: the interior of oasis is good, and the peripheral barren area is poor; The middle reaches are better, but the lower reaches are worse; The east is better than the west.

14): 1. The surface water resources utilization plan formulated by Shule River resettlement project; Second, the water resources control scheme is mainly based on the use of surface water, supplemented by groundwater; The third is the soil improvement and ecological balance scheme under the reasonable allocation of surface water and groundwater. After model analysis and calculation, the third scheme is selected as the basis of water resources allocation, and the specific contents are as follows: the total water demand of Changma, Shuangta and Huahai irrigation areas is 745.24 million m3. Among them, drinking water for urban and rural people and livestock 1 1 10,000 m3 (groundwater recharge), water demand for township enterprises is 8 million m3 (groundwater recharge), industrial water demand for No.404 plant is 82.75 million m3 (surface water recharge), and agricultural irrigation water demand is 632.33 million m3 (including surface water recharge of 477.43 million m3 and groundwater recharge of15499). The total water demand of Danghe Irrigation District is 290 million m3, surface water is 240 million m3 and groundwater is 50 million m3.

15) The phreatic water area suitable for exploitation is located in Yumen Town-Sijiatan area, the front of alluvial fan, west of Qizhen in Dunhuang Basin, which can be used as a large-scale water source for centralized exploitation. Seven towns south of Dunhuang-Wu Dun and Zhen Shi farms, and Sanjiu Company farms south of Huahai Township in the middle of Huahai Basin are suitable for scattered or contiguous mining.

The areas suitable for exploitation of phreatic water and confined water are distributed in Huanghua-Qidaogou-Tuhulu-Ziqiao area at the front of alluvial fan in Changma, between the south of Panyaoshu-Sigong-Anxi County in Anxi Basin and Shuangta Reservoir, the front of Danghe alluvial fan in Dunhuang Basin, the area of Lucaojingzi-Mengjiaqiao, and the east-west line of Gejiajing in Huahai Basin. The above-mentioned sections can be mined by layers or mixed mining as required, but the TDS of local shallow groundwater in Anxi Basin is high, so it is appropriate to strictly stop water supply and mine the lower confined water.

The confined water area suitable for mining is located in Sandaogou-Yaozhanzinan-Qiaozidong area at the front edge of Changma alluvial fan, and the confined water mining conditions are the best.

The top of Changma diluvial fan, Yulin diluvial fan and Danghe diluvial fan whose water level is above 100m is limited by economic and technical conditions, so it is difficult to mine.

Due to the high TDS and poor water quality, the northern edge of each basin and the groundwater retention area are not suitable for mining. In addition, Yumenguan in Dunhuang basin and the area south of Gushule River in the west belong to natural ecological environment protection areas, and there is no development plan, so they are classified as unsuitable mining areas.

16) The deep groundwater is fresh confined water of Neogene-Lower Pleistocene. At present, the areas with proven water supply value are mainly distributed in Yumen Town and Gong Peng area, which can be used as drinking water sources for small and medium-sized industries or urban residents (water demand is 50,000 m3/d).

The shallow groundwater in Jiuquan Formation (including Gobi Formation, the same below) of Middle-Upper Pleistocene can be used as the water source under the condition of centralized exploitation of large-scale industrial and agricultural water supply. It is best to use centralized irrigation with multi-well confluence in pure well irrigation area, and it is best to arrange water wells along branch canals in mixed irrigation area.

Shallow brackish water, especially the lower confined water, has good water quality and is an effective supplement to the water source in the peripheral development zone of the irrigation area. It is best to use it mixed with surface water, or to mine it mixed with upper diving and lower pressurized water.

Salt water has little value for exploitation and water supply.

17) changma irrigation area has developed 200,000 mu of well irrigation or mixed irrigation in the old irrigation area and the surrounding wasteland and the wasteland with suitable wells, and newly drilled agricultural irrigation wells 166, totaling 724 eyes. Groundwater is 98 million m3, with less drainage of 88 million m3. Changma Dam can abandon water to Gobi, or transfer water from the west trunk line to Shuangta Reservoir to supplement groundwater and downstream ecology.

Shuangta Irrigation Area is located in the old irrigation areas such as Lianghu Branch, Huancheng, Nancha and Guazhou to the east of Anxi County. The area of well irrigation or mixed irrigation is 6,543.38+0.266 million mu, and 654.38+0.76 agricultural irrigation wells are added, with a total of 528 eyes. The groundwater is 63 million m3, and the drainage water is 77 million m3 less. The remaining water can flow from Shuangta Reservoir to the natural channel of Shule River.

Huahai Irrigation Area has developed 54,000 mu of well irrigation or mixed irrigation in the old irrigation area, Dushanzi Farm and Bijiatan Development Zone, and newly drilled agricultural irrigation machine wells 1 12 eyes, totaling 157 eyes. Groundwater exploitation is 27 million m3, with less drainage of 26 million m3. The remaining water can be discharged from Jinchi Reservoir to Ganhaizi Lake area, so as to

In Danghe Irrigation District, agricultural water-saving measures such as drip irrigation, sprinkler irrigation and changing crop planting structure were taken to reduce irrigation quota and the number of agricultural exploitation wells, so that the groundwater exploitation was reduced to 500 million m3 and 575 exploitation wells were exploited. Among them, there are agricultural irrigation wells 196 in towns and villages south of Dunhuang, including seven towns and Yangjiaqiao township, with an output of 5.56 million m3. All agricultural irrigation wells in this area should be closed, and all irrigation tasks should be undertaken by surface water.

18) Small and medium-sized water sources of 65,438+10,000 ~ 50,000 m3/d can be built in the southwest of Yumen Town. If a large-scale water source with an area of more than 65438+100000 m3/d is built, it should be located in the alluvial fan area of Changma in the west of Yumen Town according to the water delivery requirements. The water source is the phreatic water in the gravel layer of Middle-Upper Pleistocene. Because of the abundant recharge source, high water source guarantee degree, no pollution source in the upstream of the water source and sufficient water quality guarantee, it can be used as the prospective water source of Yumen Town.

Anxi County can build 50,000 m3/d water source in the North Gobi and Shule River in the north of the county seat. If a large-scale water source above 65438+100000 m3/d is built, another water source will be built in the ancient channel of Shule River in the south of the county, and the north and south water sources will jointly operate to meet the water supply demand. Huahai Township currently has a centralized water supply system, and the water source is near Tiaohu Lake. According to its development needs, the water source area of 65438+100000 m3/d should be located at the edge of Gobi in the southwest of Tiaohu Lake, in order to avoid the pollution of groundwater in the water source area by agricultural irrigation.

The Danghe water source has been built in Dunhuang City, with a daily output of 6.5438+0 million m3 and an annual output of 3.5 million m3. The water source can be expanded to 7.5 million m3, which is the most potential area. At the same time, Qinghai Petroleum Administration Bureau has built water sources in seven towns, with an annual output of120,000 m3. At present, the proven reserves180,000 m3 have certain development and utilization prospects.