First, the regional floor funnel
(1) Nomhon
Nuomuhong Farm in the basin once formed a regional descending funnel, which has now disappeared. The farm was established in 1955, and began to mine groundwater to irrigate farmland in 1965. There are 35 wells in 1980, and the actual output in irrigation season is11.3272×104m3/d, reaching 1986. Scattered in farmland and team sites of various brigades, the actual output in irrigation season is13.9283x104m3/d, and that in irrigated farmland is1166.7 hm2 ..1986. According to the static water level and/kloc at the completion of each exploitation well, The underground water level drop funnel of the farm was drawn, and two elliptical drop funnels were formed in the mining area, the eastern funnel area was 28.26km2, the western funnel area was 34.53km2, and the static water level drop value in the central area was1.28 ~ 3.25m. Although the agricultural water supply source area of the latter was seasonally mined, the mining period was about 135d (wheat growing period). The groundwater runoff in this area is16.1917×104m3/d, which is 6.25% higher than the actual exploitation. The late stage of agricultural irrigation is the dry season, and the amount of recharge is small, and the infiltration period of agricultural irrigation has passed. The two funnels are not connected together, because a large number of floods seep and recharge in rainy season, which makes the groundwater recharge to a certain extent. The alluvial fan shaft has a large amount of groundwater runoff, during which it acts as two independent funnels to receive groundwater recharge. The exploitation and compensation here have basically reached a balance, but the existence of two funnels is long-term non-seasonal. According to the long-term observation data of groundwater from 1987 to 1997, two descending funnels have always existed.
Through the unified measurement of groundwater level in the whole basin in wet season and dry season in 2003 and 2004, the obtained groundwater data were compared and analyzed, and it was found that the groundwater in the eastern and western descending funnels of Nuomuhong farm area basically recovered. The buried depth of the central water level of the west funnel was originally 10.35m( 1982), and the static water level decreased by 2.35m m. In 2005, the buried depth of the water level was 5.74m, which was 2.26m higher than the original static water level. The buried depth of a hole near the center of the East Funnel was 16.37m( 1982), and the static water level dropped by 0.03m In 2004, the buried depth of the water level was 12.86m, which was 3.48m higher than the original static water level. The reason is that with the farm reform in Qinghai province in recent years, a large area of cultivated land on the farm has been abandoned or outsourced to individual farmers. Due to the high cost of pumping underground water and electricity, the general individual farmers are limited by economic conditions, and the amount of groundwater exploitation is gradually decreasing. Most of them are mainly irrigated by surface water, and the groundwater is fully replenished through river infiltration to restore the water level. According to the investigation in 2003, the exploitation of groundwater in this farm is 235.445438+0× 104m3/a, of which the exploitation of agricultural irrigation is 227.95438+0× 104m3/a, which is lower than that of 1980. 49867.86868686686
According to the investigation of towns and agricultural wells in various places, the groundwater exploitation in Golmud City and Delingha City is relatively large, and the groundwater exploitation in other areas is relatively small, which is not over-exploited and does not form a regional falling funnel.
(2) Chaerhan
There is over-exploitation of liquid mineral resources in Chaerhan Salt Lake area of Qaidam Basin. Due to the large-scale exploitation of intercrystalline brine in chemical plants in recent years, a regional drip bucket has been formed. According to the exploration data of Chaerhan Salt Lake, the regional descending funnels are mainly distributed on both sides of the railway north of Chaerhan Railway Station and in the eastern area, with a total area of 500km2 and a total exploitation of 2.564× 108 m3/a (Figure 8- 1).
Figure 8- 1 Isogram of Brine Buried Depth in Bieletan Section of Chaerhan Salt Lake (April 2003)
After stopping mining, the edge of the funnel still extends outward and downward, and the center rises. Because it is difficult to calculate the recharge, we can only consider it from the observation data of the descending funnel in this area. The exploitation amount has far exceeded the allowable exploitation amount, which basically belongs to drainage exploitation, which brings difficulties to salt chemical industry, such as the increase of pumping cost and the increase of brine drainage construction cost after the groundwater level drops.
Second, salt water intrusion-cold lake
Due to the low degree of development in Qaidam basin, the environmental problem of salt water intrusion only occurs in Lenghu town. The reason is that the layout of water supply sources in Lenghu Town is unreasonable, and individual mining mines are close to salt water areas.
The water source of Lenghu Town is located in the shallow diving Tibetan area about 1.2km from the alluvial fan on the north bank of Lenghu Lake. There are ***5 wells with the same depth and perpendicular to the groundwater flow direction. Before 1.987, the daily output was 5920m3. According to the investigation, the dynamic water level during mining is 1 1 ~ 13m, forming a descending funnel with a radius of 956 ~1/30m. The funnel extends all the way to brackish water and salt water area, causing salt water to flow back. According to interviews with water supply managers, it is said that the water quality is obviously salty compared with when the water source is turned on. After the groundwater quality in this water source area became salty, a new water source area was re-opened in the north of the original water source area on 1989.
Figure 8-2 Schematic Diagram of Salt Water Intrusion Caused by Unreasonable Engineering Layout in Qaidam Basin
Figure 8-3 Schematic Diagram of Salt Water Intrusion Profile Caused by Unreasonable Engineering Layout in Qaidam Basin
According to the survey, due to the migration of Qinghai Petroleum Bureau in 1990s, the population dropped sharply, and now the population is 20,800. The annual groundwater exploitation is1.28.1×1.04m3, which is nearly half of that before. Through the sampling analysis of water sources in 2002, 2003 and 2004, the water quality of some wells has become salty, and the hydrochemical type belongs to SO4 Cl (HCO3)-Ca Mg type. As the current exploitation amount is small, it is not the salt water intrusion caused by groundwater overexploitation, but the unreasonable project layout (Figure 8-2 and Figure 8-3).
Third, water salinization-Golmud
The salinization of water quality in the basin is only found in the right wing of the Gobi belt of the alluvial-diluvial fan of Golmud River. The water quality changes in the upper and lower sections of shallow groundwater in this area, which are only manifested in different hole depths and different filter placement positions in water supply wells. Although the holes are very close, the water quality varies greatly (Table 8-3). The water supply well (hole depth 66.42m) of Tibet Grain Bureau, which was built in 1990, was abandoned because four items of water quality exceeded the standard. A new well was dug at a distance of 10m from the original well, and the hole depth only increased to 10 1.08m, but the water quality was good. The depth of "boundary" between upper and lower water quality is about 80m.
The main reason of water salinization is that there is an ancient salt shell on the surface or shallow layer in this area. In the process of mining, due to pipeline leakage and other reasons, the salt in the salt shell is leached into the aquifer, resulting in salinization of water quality. In the early 1980s, the groundwater level in this area generally rose, which leached the salt from the ancient salt shell and also caused the salinization of water quality. In addition, in 1998 and 1999, the Agriculture and Animal Husbandry Bureau of Golmud City built a 60-mu windbreak belt in the upper reaches of the water source for greening the city, which was flooded, causing a large amount of salt in the vadose zone to dissolve and infiltrate, leading to a sharp increase in TDS and so on.
Table 8-3 Statistics on Vertical Differentiation of Water Quality of Right-wing Mining Mine in Gobi Zone of Alluvial Fan of Golmud River
Four. Desertification (desertification)
Qaidam Basin is a desert basin formed during the famous geological history of China. The land is vast, but the available land area is very limited. The desertification in Qaidam Basin is dominated by primary and secondary salinization, wind erosion and desertification, followed by water erosion desertification. According to the remote sensing interpretation data in 2004, the present situation of desertification in the plain area of the basin is expounded.
The desertification area in the plain area of Qaidam Basin is large and concentrated, and the degree of desertification is quite different. The surface landscape is dominated by Gobi, wind-eroded depressions, wind-eroded residual hills, aeolian crescent dunes, liangwo dunes, aeolian sandy land and sand cover. The area of desertified land in Qaidam Basin is 75736.9km2, accounting for 54% of the total plain area (Table 8-4); Among them, the lightly desertified land area is 5885.3km2, accounting for 8% of the total desertified land area; The area of moderately desertified land is 7045.9 square kilometers, accounting for 9% of the total area of desertified land. The area of severely desertified land is 62,805.7 square kilometers, accounting for 83% of the total area of desertified land. Since 1960, large-scale land reclamation, construction of roads and railways, development of mineral resources, and large-scale exploitation of groundwater have led to the decline of groundwater level in the oasis zone, the degradation of vegetation, the rapid expansion of desertification area and the intensification of desertification, which have seriously threatened industrial and agricultural production and the lives of local residents, and restricted the local economic development. A large area of farmland in the northern part of Dulan area was covered by wind and sand, and 2/3 of the cultivated land of youth farm was covered by wind and sand, so it was forced to abandon farming. The sand damage in the north of Xiangride Farm is serious, and the accumulation height of sand dunes has reached several meters. Farmland has been covered by wind and sand, and it has been forced to become woodland and shelter belt.
Verb (abbreviation of verb) Shrinking lakes-West Tai Ji Nair Lake and Tuosu Lake
Tuosunuoer, also known as Tuo Su Hu, is located in the southwest of Delingha City on the northern edge of Qaidam Basin and is a typical inland salt lake. It is an equilateral triangle with a side length of 20km, an area of 192.8km2, an average water depth of 3.5m, and the deepest point of 25.70m It is mainly replenished by its sister lake Korrak in the north, which is evaporated and discharged, and the lake area is decreasing. The TDS in the lake is rising continuously, with 196 14.4g/L on the north bank, 15.25g/L on the south bank and 1984 of 35.74g/L, belonging to Cl SO4-Na Mg type.
Xitai Jinaier Lake is located on the west side of Dongtai Jinaier Lake, with a water depth of 0.4m It is mainly replenished by Tajinaier River and groundwater in plain area, and discharged by evaporation. TDS 3 10 ~ 330 g/L belongs to Cl-Na type. Sedimentary rock salt at the bottom of the lake. Remote sensing interpretation confirmed that the lake has shrunk seriously, with the lake area of 1976 being 334.20km2, 1990 being 168. 17km2, and in 2000 being 43.37km2, accounting for 13% of the original lake area. After 25 years, the lake area has decreased by 290.83km2.
The TM data of 1990 were compared with the e TM data in 2000 in the Sugan Lake basin. The results show that in 2000, the water area of lakes in the whole basin was 1 1.73km2, of which the water area of Sugan Lake was10.28km2; ; There are 79.36km2 oases and marshes in the basin, which are mainly distributed in the front of alluvial fans in the lower reaches of the Great Hareton River in the east of Sugan Lake. The modern glacier area in the basin is 36.50km2, and the desert area is 2 10. 15km2. Compared with 1990, the water area decreased by 4.24%, the modern glaciers decreased by 27.7 1%, the oasis and swamp wetlands decreased by 6.36%, and the desert expanded by 14.32% (Figure 8-4).
Table 8-4 Statistics of Desertification Land in Qaidam Basin
The Great Hareton River has been transformed with groundwater from the mountain pass to the Tailu Lake area, and the lake and groundwater are mainly replenished by the Great Hareton River, thus maintaining the ecological environment around the lake. The Great Hareton River is relatively stable because it is replenished by glacial meltwater. If the glacier area is greatly reduced or water is diverted from the upstream to the outside of the basin, the ecological water consumption of oases and lakes in this area will be reduced, resulting in the decrease of oasis and swamp wetlands and the gradual disappearance of lakes, which will eventually lead to the overall deterioration of the ecological environment in this basin.
Figure 8-4 Comparative results of main eco-environmental factors in Sugan Lake Basin in different periods
Sixth, salinization
(A) The present situation of salinization in Qaidam Basin
According to the data of remote sensing interpretation in 2004, primary salinization is the main land salinization in Qaidam Basin, followed by secondary salinization. The total area of salinized land is 358 10.8km2, accounting for 25% of the total area of plain area. The area of primary salinized land is 35468.3km2 (Table 8-5), accounting for 99% of the total salinized land area. Mainly distributed around the lake in the center of the lake basin, the surface is mainly composed of salt crust, salt frost and salt spots, mostly in desert saline areas, followed by desert grassland saline areas.
Table 8-5 Statistics of Primary Saline Land in Qaidam Basin
The area of secondary salinized land in Qaidam Basin is 342.5km2 (Table 8-6), accounting for 1% of the total salinized area. Mainly distributed in Golmud, Nuomuhong, Golmud Township, Xiangride and other agricultural areas; The surface is dominated by salt frost, followed by salt spots, mostly in the saline soil area of desert grassland, and its distribution range is mainly influenced by seasons and controlled by human activities. The secondary salinization degree varies from place to place. The salinization degree of agricultural areas in Golmud and Delingha areas is relatively high, while that in Zongba area is relatively low.
Table 8-6 Statistics of Secondary Salinized Land in Qaidam Basin
(2) Causes of salinization
Salinization in Qaidam basin is the result of both natural and human factors. Primary salinization is completely controlled by natural factors. The climate in Qaidam Basin is a typical arid type, and the evaporation drop ratio is as high as 40∶ 1. In the historical period, the harsh desert climate and strong evaporation made the shallow groundwater zone near the surface contain a large amount of salt, forming a large area of primary salinization.
Secondary salinization is mainly controlled by human activities. Because there is little precipitation in Qaidam basin, there is no agriculture without irrigation. In agricultural areas with shallow groundwater level, after the development of artesian canal irrigation, due to unreasonable irrigation methods, such as flooding irrigation, only irrigation without drainage, the groundwater level rose to less than the critical evaporation value, the cumulative salinization degree increased year by year, and the soil salt content increased continuously, forming secondary salinized land.
Seven, groundwater pollution
The "three wastes" in towns of Qaidam Basin are mainly discharged directly, especially industrial and domestic sewage is mainly discharged into surface water bodies such as rivers, sewage ditches and ponds, which causes shallow groundwater pollution in some cities. At present, there are few highly polluting industrial and mining enterprises in groundwater and fresh water distribution areas, and the sewage discharge is not large. The pollution components in groundwater are simple, the pollution degree is not very high, and the scope is not very wide. After this investigation, it was found that lead, oil and volatile phenol were polluted in a few places. Lead only exceeds the standard in the groundwater of Dachaidan Town, and the content is 0.275mg/L, which is caused by the waste liquid discharged from boric acid plant. Oil and volatile phenol pollution are mostly concentrated in Golmud City and Huatugou Town, which are closely related to the local petrochemical industry (Table 8-7 and Table 8-8).
With the development of the city, the discharge of "three wastes" will increase, so we should pay attention to this problem.
(A) Groundwater pollution in Golmud City
Golmud is a modern emerging industrial city in the southern margin of the basin, located at the junction of Gobi and Oasis, with a permanent population of 203,600. It is the fastest growing city in the gross national product of Haixi Mongolian and Tibetan Autonomous Prefecture, and it is also the city with the most utilization of water resources in Qaidam. According to the survey, the daily water consumption of the city is 10× 104 m3/d, and the production and domestic sewage discharge is 2.33×104m3/d. These sewage are only discharged to the Donghe River and Xihe River in Golmud by the sewers laid along the main streets of the city. Where there are no sewage facilities, sewage is discharged on the spot, causing groundwater pollution in urban areas. Groundwater pollution in Golmud was first discovered in Hedong area of 1984. The pollution factors are total hardness, TDS and chloride, and the pollution area is1.47km2; : 1989 reached 8.37km2, in addition to oil and phenol pollution, the water quality in the upper section of Golmud East Water Source deteriorated rapidly, with TDS and sulfate exceeding 1 times and chloride ion exceeding 3.5 times. Although the sewage treatment plant in Golmud City has been completed, the domestic sewage and industrial wastewater discharge facilities are lagging behind, and the problem of groundwater pollution still exists.
Table 8-7 Groundwater sampling points with oil content ≥ 0.05 mg/L in Qaidam Basin
Table 8-8 Volatile Phenol Content in Qaidam Basin >: 0.002mg/L Groundwater Sampling Point
The most serious groundwater pollution is oil pollution, and its pollution source is mainly Golmud-Lhasa oil pipeline. The oil pipeline was built in 1980s and laid along the Golmud River, with a length of about 150km and three pressurized pumping stations. Because the oil pipeline is in disrepair for a long time, the pipeline leaks oil, the waste oil from the pumping station is discharged, the surface water is polluted first, and the river water seeps into the ground and then pollutes the groundwater. According to the monitoring data in April, 2003, the oil content in the groundwater of Golmud alluvial-diluvial fan is 0. 13 ~ 0.89 mg/L, and the detection rate of samples is 100% (Figure 8-5). Compared with 2002, the oil pollution has decreased, and the pollution scope is still the same as last year. The main reasons for reducing oil pollution are the transformation of oil pipelines and the reduction of waste oil discharge from pressurized pumping stations.
Fig. 8-5 Duration Curve of Petroleum Content in Groundwater in East Water Source Area of Golmud City
(2) Groundwater pollution in the rest of the basin.
The exploitation of mineral resources in this basin is in the primary stage. Except Golmud City and Delingha City, other towns have a small population; Industrial and mining enterprises are scattered, and the discharge of domestic and production wastewater is not large. It is difficult to determine the degree of water pollution due to the lack of background information on groundwater quality in most towns. As a source of groundwater pollution, it exists in almost every town, while sewage and industrial wastewater are discharged locally. Except Golmud Sewage Treatment Plant, there are no sewage treatment facilities in other towns and villages.
Huatugou town. The main pollutants in this area are sewage discharged from oil production plants, and the main pollution indicators are mainly petroleum. According to the investigation in 2003, the daily sewage discharge reached 1, 348. 1.8m3/d, which was discharged locally and infiltrated into the piedmont Gobi without any effective treatment.
Xitieshan industrial wastewater The pollution sources in this area are mainly the washing wastewater from lead-zinc mine area, the wastewater generated during mining and the wastewater discharged from thermal power plants. The sewage discharge is 5.77 1× 104 m3/a, 52.22× 104 m3/a and 78.43× 104 m3/a respectively, and the total discharge reaches136.42×/kloc. If sewage treatment is not carried out, Chaerhan Salt Lake will be polluted.
Dulan county. There are 7 mineral processing plants around dulan county, including 3 lead-zinc mineral processing plants and 4 iron ore plants, of which 2 are in the upper reaches of Xiaha River and 5 are in the upper reaches of Chahanwusu River. These mineral processing plants are township-run or self-employed, with simple facilities and low production technology, and the wastewater for mineral processing is discharged on the spot without treatment. Dulan county City and Xiariha Town are located in the downstream of pollution sources, and relevant departments should attach great importance to them.
Dagele Township in Golmud City is located at the junction of dulan county and Golmud City, and the upper reaches of Dagele Gully and Xiaowulonggou are under the jurisdiction of dulan county. At the end of 1990s, due to the discovery of Wulonggou gold mine (rock gold), a large number of ores were mined and cyanide was used for gold heap leaching. On the southern slope of Xiaowulong Valley, there is a cyanide waste liquid sedimentation tank with an area of 0.3km2. The lower part of the sedimentation tank has no effective seepage control measures, and the surface is silty sand and the lower part is gravel, which is a great potential threat to groundwater. The pollution source is still there, which should attract the attention of relevant departments.
Eight, groundwater resources attenuation
(a) The impoundment of the project reduces the groundwater recharge.
The formation and distribution of water resources in Qaidam basin is characterized by repeated transformation of water resources in mountainous areas in plain areas. The Huaitoutala Reservoir in Delingha City was built at the exit of the Barron River, which intercepted all the river water and introduced it into the river. Except for a small amount of leakage under the reservoir dam and channel leakage, not much river water can penetrate into the ground during the flood period, so the groundwater resources in this area are greatly reduced.
The depletion of groundwater resources caused by diversion canal is also common in all irrigation areas in the basin. The groundwater resources of alluvial-diluvial fans in the basin mainly depend on the leakage of river water. When river water is introduced into the channel, most or all of the river water runs in the channel, and its leakage is far less than that of natural rivers. According to the survey, the water level of Xiangride Farm/KOOC-0/well was 77.27 m (/KOOC-0/974 August 3/KOOC-0/) when it was completed, and the measured water level in August 2003 was/KOOC-0/June 987/KOOC-0/00.33 m.
(b) Groundwater resources may decrease due to changes in natural conditions.
Modern glaciers are widely distributed in the mountainous areas of Qaidam Basin, with a total area of 1358.46km2, glacier reserves of1135x108m3, and annual melting water of glaciers of 9. 18× 108 m3, accounting for rivers in Qaidam Basin.
Affected by the global temperature rising continuously, the average temperature in the plain area of the basin is generally on the rise, with the ratio of 0.0 155 ~ 0.062℃/a, and the annual average temperature in mountainous areas will also continue to rise, the climate will gradually get warmer, and the glacier shrinkage trend in this area will intensify. For example, Kaketumunke Glacier in Qilian Mountains, with the highest elevation of 5696m, 1993 glacier area of 44.5km2, decreased to 40.9km2 in 20065438+0; It has decreased by 3.6km2 in 8 years, with an average annual decrease of 0.45km2, and the shrinkage rate is 1.0 1% (Figure 8-6). If the temperature continues to rise, a large number of glaciers in alpine regions will melt, which will increase river runoff and increase groundwater infiltration and recharge in a short time; When the glacier shrinks to a certain extent, the flow of the above rivers replenished by glacial meltwater decreases, and the groundwater recharge in the downstream decreases, which weakens the groundwater resources.
Fig. 8-6 Comparison of glacier shrinkage 1976 and 200 1 glacier area in Beishan.