Located in the northeast of Qinghai-Tibet Plateau, Qaidam Basin is a typical inland arid basin surrounded by high mountains, with Altun Mountain in the northwest, Qilian Mountain in the northeast, Kunlun Mountain in the south and Ela Mountain in the east. Saishiteng Mountain, Xitieshan Mountain and A Mu Nik Mountain in the middle of the basin divide the main basin into Ga Schooler Lake, Sugan Lake, Mahai, You Xiang, Dachaidan, Delingha, Wulan and Chahanwusu sub-basins, forming a special landscape in which the basins are connected. Macroscopically, extremely high mountains, mountains, hills, piedmont flood plains, flood plains, lacustrine plain and lacustrine plain are developed from the periphery of the basin to the center, and swamps, salt marshes and lakes are superimposed on lacustrine plain and lacustrine plain.
(A) groundwater function evaluation index system
In the evaluation index of groundwater resources function in Qaidam basin, the indexes related to groundwater reserve resources are not considered. In the evaluation of ecological environment function, three aspects are mainly considered: lake and marsh landscape, vegetation and land. In Qaidam Basin, due to the small scale of groundwater exploitation, the geological environment effect of groundwater is not obvious. Except for local salt water intrusion caused by unreasonable well location in Lenghu Town, no land subsidence and salt water downward movement occurred in other areas. In the attenuation of groundwater system, considering that the increase of groundwater salinity in Qaidam Basin is related to the depth and intense evaporation of groundwater, the spring flow is mainly affected by the change of groundwater level, which is mainly controlled by groundwater infiltration and recharge, the correlation between groundwater quality and water level, the correlation between spring change and groundwater, and the ratio of groundwater recharge variability to water level change are selected (Figure 8- 15).
(2) groundwater function evaluation zoning
The groundwater system in Qaidam basin is evaluated as a unified whole. According to the burial conditions of the groundwater system and the development and utilization of groundwater, the basin is divided into 14 primary zones, 47 secondary zones and10/3 tertiary zones (Figure 8- 16). Each first-class area maintains a complete groundwater recharge, runoff and drainage circulation system. The primary area is divided into secondary areas according to hydrogeological conditions, mainly based on the distribution of groundwater hydrochemical field and the groundwater system conditions in the secondary basin. The secondary zone is divided into three zones (zones) according to the recharge, runoff and discharge conditions of groundwater. On this basis, 27,933 effective units were divided by using 2×2km2 grid and numbering them uniformly.
Fig. 8- 15 groundwater function evaluation index system in Qaidam basin
Fig. 8- 16 zoning map of groundwater function evaluation in Qaidam basin
(III) Evaluation results of groundwater function
1. The functional status of groundwater resources
See Figure 8- 17 for the evaluation results of groundwater resources function in Qaidam Basin. The resource function of groundwater is the strongest in the recharge runoff belt of Nalinggole River Basin, but it is stronger in the recharge runoff belt of the downstream basin, Golmud River Basin and Tataling River Basin. However, the resource function of groundwater is weak in cold lake basin and complete basin. Among them, the function of groundwater resources in salt water distribution area is the weakest. In this basin, the suitable scale mining area is only distributed in the groundwater recharge runoff area of Nalinggol River Basin, and the centralized mining area is mainly distributed in the drainage area of Nalinggol River Basin, Golmud River Basin and Tataling River Basin. In the distribution area of salty brine, it has become a liquid deposit, not a fresh water resource, and it is an unexploitable area.
Figure 8- 17 Functional Distribution Map of Groundwater Resources in Qaidam Basin
2. Ecological function of groundwater
The evaluation results of groundwater ecological function in Qaidam Basin are shown in Figure 8- 18. The ecological function of groundwater in drainage zone of each basin is strong, but the ecological function of groundwater in recharge runoff zone is weak, and the ecological function of groundwater is the strongest, mainly distributed in oasis zone. When the level of groundwater ecological function is higher than the average level, the development and utilization of groundwater must pay attention to the protection of groundwater ecological function, and the development and utilization of groundwater should be based on the protection of groundwater ecological function.
3. The role of groundwater geological environment
See Figure 8- 19 for the evaluation results of groundwater geological environment function in Qaidam Basin. In the oasis belt of each basin and its adjacent areas, the geological environment function of groundwater is strong. However, in the saline water distribution area downstream of the oasis belt, the geological environment function of groundwater is general. In the oasis belt, because the spring water is widely distributed, the change of groundwater level has a great influence on the spring water dynamics, so the groundwater in the oasis belt has a strong geological environment function. Therefore, attention must be paid to the protection of groundwater geological environment function when developing and utilizing groundwater in this area.
4. Sustainability of groundwater comprehensive function
Combined with the resource function, ecological function and geological environment function of groundwater, the sustainability evaluation results of groundwater comprehensive function in Qaidam Basin are obtained, as shown in Figure 8-20. The areas with strong groundwater sustainable utilization ability are mainly distributed in the recharge runoff areas of Naling Guole River, Golmud River and Tataling River. The advantages of groundwater resources in these areas are obvious, but the ecological and environmental functions of groundwater are weak. The sustainable utilization of groundwater in the piedmont recharge runoff area of other basins is generally-strong, and the groundwater in the recharge runoff area in the middle of Qaidam Basin and the saline water distribution area in drainage areas of various basins is the weakest, and the areas with weak sustainable utilization of groundwater are mainly distributed in oasis areas in drainage areas of various basins.
Figure 8- 18 Distribution Map of Groundwater Ecological Function in Qaidam Basin
Figure 8- 19 Distribution Map of Groundwater Geological Environment Function in Qaidam Basin
Figure 8-20 Distribution Map of Groundwater Comprehensive Function Sustainability in Qaidam Basin
(4) groundwater function zoning
According to the evaluation results of groundwater function in Qaidam Basin, it is divided into three secondary zones and eight tertiary zones (Figure 8-2 1).
1. groundwater resource functional area
Groundwater resources in Qaidam Basin can be exploited on a large scale, mainly distributed in the recharge runoff zone of Nalinggole River Basin and Golmud River Basin (Figure 8-2 1). The above two areas have strong ability of sustainable utilization of groundwater resources, and the function of groundwater resources is dominant. Groundwater is basically not directly related to the surface ecological environment and geological environment, which can provide a large number of groundwater fresh water resources and arrange water sources on a large scale.
The centralized groundwater exploitation area in Qaidam Basin is mainly distributed in the groundwater recharge runoff zone or runoff zone around the basin. Include recharge runoff belt and runoff belt in Ga Schooler Lake basin, groundwater recharge runoff belt in Dalangtan Basin, groundwater recharge runoff belt in Lenghu Basin, groundwater recharge runoff belt in Mahai Basin, groundwater recharge runoff belt in Dachaidan Basin, groundwater recharge runoff belt in Tataling River Basin, groundwater recharge runoff belt in Xiaochaidan East Basin, groundwater recharge runoff belt in Barongele River Basin, groundwater recharge runoff belt in Bayingole River Basin, groundwater recharge runoff belt in Gahai Lake, The recharge runoff zones of Keke Salt Lake-Dulan Lake Basin, Mangya Lake Basin, West Dabson Lake Basin, Tola Haihe River Basin, Hongliugou-Dashuigou Basin and South and North Huolusong Lake Basins (Figure 8-2 1). The sustainable utilization of groundwater resources in such areas is strong, the function of groundwater resources is dominant, followed by ecological function and geological environment function, and groundwater fresh water resources are relatively rich, which can concentrate small and medium-sized water sources. The relationship between groundwater and surface ecology and geological environment is not obvious, and a large number of groundwater exploitation will not cause disastrous ecological or geological environment problems.
Fig. 8-2 1 regional distribution map of groundwater comprehensive function sustainability in Qaidam basin
Groundwater resources in the Qaidam Basin are distributed in scattered mining areas around the Qaidam Basin in patches, including groundwater runoff zones in Dalangtan Basin, Bayingole River Basin, Bayingole River Basin, Huahaizi River Basin, Quanzu River Basin and Shaliu River Basin (Figure 8-2 1). The sustainability of groundwater in these areas is general, and the conditions of groundwater resources are general. Although it is not conducive to the development and utilization of groundwater, there are no obvious ecological and geological environmental problems in this area. The function of groundwater resources is dominant among the three functions, and it is also an important water source in arid inland basins. So small-scale mining can be dispersed.
2. Groundwater ecological function area
The ecological functional zones of groundwater in Qaidam basin are mainly distributed in the drainage area in the center of the basin and the recharge runoff area in individual basins. Groundwater in these areas plays a strong role in maintaining surface wetlands, lake landscapes, vegetation and soil, and all the attributes of ecological functions are basically in a strong state in these areas, while the functions of groundwater resources and geological environment are relatively weak. According to the particularity of ecological problems in different regions, it is divided into vegetation protection areas, landscape protection areas, land protection areas and landscape development areas.
In the vegetation protection area of Qaidam Basin, the ecological function of groundwater is dominant, and the maintenance of vegetation environment is dominant in the ecological function attributes of groundwater in this area, and the maintenance of vegetation environment by groundwater is in a general-strong state. Mainly distributed in the oasis belt of the basin, Including Timur River Basin, Kuangou-Baozigou River Basin, Lenghu River Basin, Huahaizi River Basin to the east of Sugan Lake Basin, Xiaosugan Lake Basin, Mahai River Basin, Dachaidan River Basin, Yike Qaidam Lake Basin, Tataling River Basin, Barongegol River Basin, Bayingol River Basin, Shuangshixia-Hongyahuo River Basin, Mangya Lake Basin, Bayingol River Basin, and so on. Tola Haihe River Basin, Golmud River Basin, Hongliugou-Dashuigou Basin, Liusha River Basin, Nomuhong River Basin, Chahanwusu River Basin, Hongshui River-Iquole River Basin and Xiangride River Basin. Groundwater in these areas is the water of life in oases, and it is almost the only water source for vegetation in oases. Oasis is the most suitable green life zone for human habitation, production and life in the whole basin. Therefore, shallow water in these areas is not suitable for large-scale exploitation, and the ecological water level of groundwater should be reasonably regulated to protect the ecological balance of oasis.
The ecological function of groundwater in the landscape protection area of Qaidam basin is dominant, and the landscape environment maintenance and water environment correlation are dominant in the ecological function attributes of regional groundwater, and the landscape environment and water environment groundwater remain strong-strong. Lake drainage belts mainly distributed in the center of the basin include Ga Schooler Lake groundwater runoff belt, Ga Schooler Lake groundwater drainage belt, Dasugan Lake groundwater drainage belt, Dasugan Lake groundwater drainage belt, Huahaizi Basin groundwater drainage belt and the first drainage belt west of Sugan Lake, Dezong Mahai Lake groundwater drainage belt, Bajia Qaidam Lake groundwater drainage belt, Bajia Qaidam Lake groundwater drainage belt, Tuo Su Hu groundwater drainage belt and Saishike River. Keke Salt Lake-Dulan Lake Groundwater Discharge Belt, Dulan River Basin Groundwater Discharge Belt, Mangya Lake Groundwater Discharge Belt, Shuangshixia-Hongyahuo Basin Groundwater Discharge Belt, East and West Taiwan Jinaier Lake Groundwater Discharge Belt, West Dabusong Lake Groundwater Discharge Belt, East Dabusong Lake Groundwater Discharge Belt, South and North Horusong Lake Groundwater Discharge Belt. Groundwater in these areas plays an obvious role in maintaining surface lakes and wetlands, and most of them are salty water with high salinity, which is not suitable for development and utilization. Therefore, these areas are mainly landscape protection.
In the land reserve of Qaidam Basin, the ecological function of groundwater is obvious. Among the ecological function attributes of groundwater in the region, the correlation between land and environment is dominant, and groundwater maintains the land environment as strong-strong. These areas are mainly agricultural land in shallow groundwater burial areas of the basin, including the northern part of the groundwater runoff belt in Golmud River Basin, the northern part of the groundwater recharge runoff belt in Hongliugou-Dashuigou Basin, the northern part of the groundwater recharge runoff belt in Nomuhong River Basin and the southern part of the groundwater recharge runoff belt in Bayingole River Basin. The eco-environmental problems in these areas are mainly reflected in the fact that farmland irrigation mainly depends on surface water and adopts traditional flood irrigation methods. Due to poor drainage and rising groundwater level, soil secondary salinization is serious. Therefore, the existing irrigation methods should be changed, surface water and groundwater should be mixed for irrigation, groundwater should be exploited appropriately, water level should be lowered, and land quality should be protected and improved.
In the landscape development zone of Qaidam basin, the ecological conditions are poor, but due to the special climate of Qaidam basin, this area has special wind erosion landform, which can be used as tourist landscape development. These areas are mainly distributed in the groundwater runoff zone of Dalangtan Dry Salt Lake, the groundwater drainage zone of Dalangtan Dry Salt Lake, the groundwater runoff zone of Salt Lake-Lenghu Lake and the groundwater runoff zone of Jinaier Lake in the east and west. The sustainable utilization of groundwater resources is poor. Compared with other areas in the basin, the functions of groundwater resources, ecology and geological environment are in a weak position. It is the worst ecological environment in Qaidam Basin, and it is also the sand source area of Qaidam Basin, with large-scale wind erosion landform. The famous ghost town in Qaidam basin belongs to this area, and it can be used as a tourist landscape development zone according to its special landform.
3. Groundwater geological environment function area
In the groundwater geological environment function area of Qaidam Basin, attention should be paid to protecting the groundwater geological environment function, and the ecological function of groundwater can be selectively protected. In these areas, it is necessary to demonstrate whether it is suitable for exploitation and utilization of groundwater and reasonably determine the recoverable amount of groundwater.
As mentioned above, the geological environment problems of groundwater in Qaidam Basin mainly appear in the east of the groundwater drainage zone in Lenghu Basin, which is mainly manifested in the large-scale exploitation of groundwater, resulting in a sharp drop in groundwater level and a backward flow of salt water in the downstream. Therefore, this area is regarded as a functional area of groundwater geological environment, and named as saline water intrusion area (B3- 1). Although the area is very small, it has little impact on the whole basin, but it is of warning significance to separate the groundwater exploitation near other salty and fresh water interfaces in the basin.