Keywords: groundwater; Water resources; Shanxi province
Shanxi province is short of surface water resources and the guarantee rate is low. According to the Water Resources Evaluation of Shanxi Province published in 2005, the total river runoff in Shanxi Province (1956 ~ 2000 series, the same below) is 8.677 billion m3, of which the available amount is 510.87 billion m3; The total groundwater resources are 8.635 billion m3, of which the exploitable amount is 5.003 billion m3. In 2000, 200 1 year and 2002, the total water supply in the province was 5.685 billion, 5.758 billion and 5.750 billion m respectively. 3, of which the groundwater supply is 3.564 billion, 36./kloc-0.60 billion, 36./kloc-0.70 billion m3, accounting for 62.7%, 62.8% and 62.9% respectively. Yuncheng City and Taiyuan City have a high proportion of groundwater recharge, reaching 75% and 80% respectively. All the domestic water for residents in major cities in this province is supplied by groundwater. ?
The dynamic observation of groundwater in Shanxi Province began at 1976, and has a history of 30 years. During this period, the well pattern of groundwater level observation has changed several times. There are 780 foundation wells in front of the project, which are divided into daily observation, 5-day observation, 10 observation and automatic monitoring. In addition, 2,500 wells were recorded. The observation data since 1980 are relatively complete, which can be used to analyze the dynamic characteristics of groundwater and calculate the groundwater resources.
1 Analysis of groundwater dynamic characteristics
The basic well data of nearly 2 1000 eyes (times) observed in the whole province from 1980 to 2000 * * 2 1 and the logging observation data of 15 are used to analyze the basic characteristics of groundwater dynamics in the whole province.
The dynamic classification of groundwater level is 1. 1
The factors affecting groundwater dynamics can be divided into two categories: natural factors and human factors. Natural factors are mainly periodic changes, but in the short term they are mainly accidental changes; However, human factors are mainly accidental, and their effects can be accumulated. According to the comprehensive analysis of groundwater observation data, the basic feature of the dynamic change of groundwater level in Shanxi Province is continuous decline, and its influencing factors mainly include:
(1) precipitation. Precipitation is the main factor affecting groundwater dynamics. When the rainy season comes, the precipitation infiltration recharge increases and the groundwater level rises accordingly; In the dry season, the infiltration recharge decreases and the groundwater level drops sharply. Under normal circumstances, the precipitation is large and the water level rises greatly; At the same time, the appreciation of water level is related to precipitation intensity, precipitation size, soil water content before precipitation, groundwater depth, soil quality and unsaturated zone thickness. ?
(2) Human factors. With the development of national economy, human activities have a great influence on groundwater dynamics. The development and utilization of industry and agriculture, especially the destruction of groundwater storage conditions by coal mining, is the main factor causing the decline of groundwater level. The leakage of canal system in each irrigation area and the infiltration recharge of field irrigation will cause the groundwater level to rise.
(3) Geological factors. Under the same meteorological factors, different aquifer lithology and topographic conditions can make the groundwater dynamics in the same climate zone obviously different. When the topography is gentle and the aquifer permeability is weak, the diving performance shows obvious seasonal variation; On the contrary, when the topography is cut strongly and the aquifer is permeable, the seasonal variation of diving power is small. ?
Under the comprehensive action of the above factors, different groundwater level hydrographs are formed, and their morphological classification is as follows:
(1) Deep buried stable type. It is mainly distributed in the hilly areas on the edge of each basin and the middle and upper parts of alluvial fans. The groundwater in these areas is deep (generally above 20 m), and there are few human disturbance factors, which basically belong to natural power type. During the year, the fluctuation of groundwater level is small, ranging from 0.2m-0.5m every year, and the hydrograph of groundwater level is linear. The source of groundwater recharge in these areas is mainly atmospheric precipitation, without evaporation and discharge, and it is only replenished to low-lying areas through runoff. ?
(2) Agricultural irrigation mining fluctuates greatly. It is mainly distributed in areas with high groundwater exploitation intensity in pure well irrigation areas or well-canal dual irrigation areas on inclined plains, such as Changyuanhe, Hongshan, Xiaohe and Wenyuhe irrigation areas and pure well irrigation areas in Taigu, Qixian, Fenyang and Jiexiu counties. When the amount of local groundwater exploitation is large, the change of water level is obviously affected by exploitation. The mining period is generally from March to 10, and the groundwater level drops sharply. Even if there is precipitation infiltration recharge in the first half of the rainy season, the decline can only be relatively reduced, and the groundwater level rarely rises. The high water level period in a year will not appear until after 65438+February, so seasonal groundwater exploitation and precipitation play a controlling role in groundwater dynamics. ?
(3) Shallow-buried seepage wave pattern. It is mainly distributed in the river irrigation area at the front of alluvial plain or alluvial fan and the area with less groundwater exploitation in well-canal dual irrigation area. They are widely distributed in the Sushui River Basin, Datong Basin, Xinjiang, Hejin and Jishan counties of Yuncheng in the lower reaches of Fenhe River, and are distributed in blocks in Linfen, Taiyuan, Ding Xin and Changzhi basins. ?
This kind of area is flat, which is the collection and discharge area of surface water and groundwater. Sources of groundwater recharge include atmospheric precipitation, irrigation water infiltration and groundwater recharge around; The main ways of excretion are evaporation and manual mining and drainage. Therefore, the fluctuation of groundwater level is closely related to the seasonal changes of precipitation and irrigation water consumption. The highest water level appears in the late rainy season or in the period when irrigation water consumption is low, and the lowest water level appears in June and July when crops need more water.
(4) overexploitation and decline. It is distributed near towns, areas where industrial and agricultural water is concentrated, or areas near wells where deep water is exploited and utilized by industry. Because the underground aquifer in the mining hole is not closed, a large amount of deep confined water is exploited by industrial and urban domestic water, which leads to the decline of the surrounding groundwater level. The water level of this kind of well continues to decline, and the year-end difference (1 annual water level decline) is greater than 1 m, and the annual change is almost equal to the year-end difference, that is, the highest water level and the lowest water level are at the beginning and the end respectively in a year, and the hydrograph is diagonally decreased. Overexploitation of deep groundwater makes the surrounding groundwater level drop sharply, forming a funnel or a permanent funnel. ?
1.2 Basic groundwater flow direction
(1) basin. Shanxi Province is located in the Loess Plateau, with the main stream of the Yellow River surrounding the western and southern edges of the province, Taihang Mountain in the east and the Great Wall in the north. Except for a few rivers flowing from Inner Mongolia Autonomous Region in the northern part of the province, the rest of the surface water systems are diverted to the west, south and east, or flow into the main stream of the Yellow River or into the North China Plain. Affected by topography, the flow direction of groundwater is basically the same as that of surface water. Tian Yang basin, Datong basin, Ding Xin basin, Taiyuan (Jinzhong) basin, Linfen basin and Yuncheng basin are in sequence from north to south, with an overall trend of NE-SW, and there is also a Changzhi basin in the southeast of the province. The groundwater flow direction in each basin has not changed fundamentally in the near future, but it collects from the periphery of the basin to the center of the basin and discharges from the upstream to the downstream. It is worth pointing out that in recent 20 years, the groundwater in each basin has been continuously and greatly over-exploited, which has led to the emergence of groundwater falling funnels in all basins, thus changing the groundwater flow direction in some areas, that is, gathering from the periphery of groundwater falling funnels to the center. With the expansion of the falling funnel, the buried depth of the central water level increases, and the influence area of groundwater flow gradually expands, but this does not change the general direction of groundwater flow. ?
(2) Hilly areas. The flow direction of groundwater in hilly areas of Shanxi Province is basically controlled by topography and geological structure, and its movement direction can be summarized as follows: first, lateral recharge to basins and mountainous rivers; The second is to sneak into the main stream of the Yellow River; Third, the collection of main karst springs. According to statistics, the exposed area of carbonate rocks in the province is 3 1 10,000 km? 2, accounting for19.8% of the total area of the province; 19 karst spring area is 64 396 km? 2, accounting for 4 1. 1% of the total area of the province, it can be seen that the recharge areas of major karst spring areas are not all exposed carbonate rocks, and a considerable part of them are covered by other rock formations.
2 secondary environmental geological problems caused by groundwater development and utilization
2. 1 The groundwater level continues to decline?
From 198 1 to 2004, the groundwater level in great basin continued to decline. Although it occasionally increased during this period, it could not change the overall downward trend, and the groundwater level continued to increase. The average groundwater table in the whole province increased from 8.69 m in 198 1 to 12.6 1 m in 2004, and the groundwater level decreased by 3.92 m, with an average annual decrease of 0. 16? M. Among them, the buried depth of groundwater in Taiyuan Basin 198 1 year is 10.25 m, and in 2004, it was 19. 12 m, and the groundwater level dropped by 0.37 m every year on average, which is the largest area in the province. Groundwater drop funnels have been formed around big cities, especially in Fangshan District of Taiyuan City, Songgu District of Jiexiu City and Yuncheng City. By the end of 2000, the total area of underground water funnels in the whole province has exceeded 1 10,000 km2.
2.2 Overexploitation is serious.
With the development of Shanxi's national economy, the demand for water resources is increasing year by year, and the exploitation of groundwater is also increasing. In the total water supply of the province, the proportion of groundwater supply has increased from 65438+4 1.4% in 0980 to 62.9% in 2002. At present, the exploitation and utilization of groundwater in the whole province (the ratio of groundwater exploitation to groundwater exploitation) has reached 72.42%, of which 89.49% is in the Yellow River basin, which has reached an unbearable level.
2.3 Severe land subsidence
Cities in the province with groundwater as the main water supply source, such as Taiyuan, Datong, Yuncheng and Jinzhong, have experienced different degrees of land subsidence. For example, in Wu Jiabao Village, Taiyuan City, the land subsidence 1 ~ 1990 10 years, and the annual subsidence reaches1300mm; In the urban area of Taiyuan, the ground generally sinks over 400 mm.
2.4 Spring water is reduced or even cut off.
Since the 1970s, with the rapid development of industry and agriculture, many spring areas have established or expanded water sources, and even drilled wells in recharge areas and runoff areas of karst spring areas, greatly reducing the original spring water volume. In addition, in recent years, the precipitation in Shanxi Province is generally low, which directly affects the recharge of karst water, leading to the continuous decline of the main karst spring water in the province. The famous Lancun Spring and Jinci Spring in Taiyuan have been cut off at 1988 and 1994 respectively.
2.5 groundwater pollution has intensified.
The continuous high-intensity overexploitation of groundwater leads to the increase of surface water leakage into groundwater. The sewage discharge of the whole province increased from 550 million m3 in 1980 to 945 million m3 in 2000, of which 689 million m3 was discharged into rivers. 13 pollutants were detected in groundwater, including ammonia nitrogen, sulfate, nitrate nitrogen, nitrite nitrogen, manganese, permanganate index, iron, fluoride, volatile phenol, total hardness, salinity, hexavalent chromium and chloride, among which ammonia nitrogen, sulfate and total hardness were the most common pollutants. In 2000, 28 main water sources in this province were tested. The results show that the water quality reaches the standard of 12, and the compliance rate is 43%. There are 16 places that exceed the standard, and the over-standard rate is 57%. Among them, 14 karst spring water source exceeded the standard in three places.
3 conclusion?
Through the observation of groundwater dynamics, we can not only grasp the groundwater level, buried depth and movement, but also further study the laws of regional groundwater dynamics (including quantity and quality) through dynamic analysis, predict the future development trend of groundwater, guide the development and utilization of groundwater resources, and avoid the passive situation caused by improper development and utilization as much as possible. ?
Author: Wu (1957-), female, from Taiyuan, Shanxi, engineer, mainly engaged in hydrology and water resources research.
Source: People's Yellow River, May 6, 2007