(Henan Institute of Hydrogeology Engineering Geology, Xinxiang, 453002)
On the basis of analyzing a large number of related data of predecessors, through the comprehensive hydrogeologic survey of1∶ 50,000, groundwater dynamic field survey, geophysical exploration, pumping test and water quality test, the hydrogeologic conditions of the spring area are basically found out, the boundary and nature of the spring area are determined, the filling diameter and discharge conditions of the spring are found out, and the natural and human factors affecting the decrease of the flow of Xiaonanhai spring are emphatically analyzed.
Key words: groundwater exploitation in Hongqi Canal, Xiaonanhai spring area, spring flow precipitation
Anyang is located in the middle and upper part of Huan River alluvial fan in northern Henan, and it is an important industrial city in northern Henan. At present, it has formed a complete industrial system of metallurgy, electric power, electronics, light industry, textile and medicine. With the development of economy, the demand for water resources is increasing. Xiaonanhai Spring, as one of the main water supply sources in Anyang City, is regulated by Zhangwu Reservoir and supplied to Angang, power plant, fertilizer plant and other enterprises and Wanjin Irrigation District. It is also the main planned water source for urban domestic water. Due to the serious phenomenon of well drilling, coal mining and mining in the spring area, the hydrogeological conditions have changed greatly, the vegetation has been destroyed, the ecological environment has deteriorated, and the spring output has decreased year by year. In the 1970s, it was 8.03 cubic meters per year. It was 5.62 m3/s in 1980s and 4.48 m3/s in 1990s. Before July 2000, the weather continued to be dry, and the spring flow in the South China Sea was only 1.95m3/s, which caused serious water shortage in Anyang City and posed a serious threat to industrial and agricultural production in Anyang City.
1 Overview of regional hydrogeological conditions
Xiaonanhai Spring is located in the transition zone between Taihang Mountain Uplift and North China Plain Subsidence Zone, starting from Xishan Fault in Linzhou in the west and Tangxi Fault in the east, and the land sandwiched between them is a structural fault block descending step by step from west to east. From west to east, it can be roughly divided into three relatively independent hydrogeological units; Taking the Xishan fault in Linzhou as the boundary, the hydrogeological unit in the bedrock area is composed of Archean metamorphic rocks and Sinian quartzite sandstone to the west of the fault. On the east side of hydrogeological unit in bedrock area is karst hydrogeological unit composed of CAMBRIAN and Ordovician carbonate rocks. The unit exposed intrusive diorite locally in Linzhou basin and depression zone, and was covered by Cenozoic sediments. It is divided into clastic sedimentary hydrogeological units consisting of conglomerate, sandstone, limestone, mudstone and shale in Carboniferous, Permian and Tertiary strata, with the contact between Ordovician and Carboniferous and Permian strata extending in the near north-south direction as the boundary.
Regional deep faults not only control the distribution of hydrogeological units, but also control the boundary of karst groundwater spring system, which divides karst groundwater system into several systems. For example, the Xishan fault in Linzhou, starting from Cambrian and Ordovician in the east and reaching Archaean in the west, forms a water-resisting boundary of karst water, which separates this karst water system from the karst water system in Xin 'an Spring Area in Changzhi, Shanxi. The fault bundle in the east of this work area is the intersection of Ordovician in Xipan area and Carboniferous and Permian in Dongpan area, forming the water-blocking boundary in the east of karst water. Karst water from the west is blocked by sandstone and mudstone, concentrated in the low-lying valley and discharged from the stratum to form karst springs. From south to north, the work area can be divided into four karst water subsystems: Shimensi Spring Area, Xujiagou Spring Area and Pearl Spring Area. Most of the spring areas are separated by groundwater watershed boundary, surface water watershed boundary and stratum water-blocking boundary.
According to the investigation, Xiaonanhai spring area covers an area of 934.6km2, with intrusive rock water-resisting boundary in the north, stratum water-resisting boundary in the east, groundwater ridge boundary in the south and surface watershed (fault water-resisting boundary) in the west.
Analysis and determination of spring flow
All the spring water from Xiaonanhai flows into Zhangwu Reservoir for industrial production and agricultural irrigation in Anyang Iron and Steel Plant and Power Plant. According to the analysis of the existing data, the spring flow has an obvious decreasing trend. These data are obtained according to the discharge of Nanhai Reservoir, the inflow and outflow of Zhangwu Reservoir, and the relationship curve between reservoir water level and discharge. According to the principle of water balance, reduce and calculate the inflow. Because it is difficult to accurately calculate the leakage, siltation and gate control error in the reservoir area, the calculation accuracy is limited. When analyzing and sorting out the original data, it is also found that when the outflow of Zhangwu Reservoir is large, the calculation deviation of inflow is large. Considering the above factors comprehensively, the least square method is used to eliminate the abnormal values in data utilization, and the discharge and precipitation of the two reservoirs are compared day by day. The daily flow of spring water is selected from the inflow of Zhangwu Reservoir when the outflow of two reservoirs is relatively stable or there is no water discharge or rainfall, and the monthly flow is selected from the average inflow of Zhangwu Reservoir. Because there are many factors affecting the flow value, it is inevitable that there are differences between the calculated spring flow value and the actual value, but the overall change trend is consistent with the actual situation.
3. Analysis of factors affecting spring flow
After this investigation and comprehensive analysis of previous data, the main control factors affecting spring flow are as follows.
3. 1 natural factors
3. 1. 1 precipitation
The influence of precipitation on spring flow is mainly manifested in two aspects. One is to recharge the groundwater in the spring area by infiltration, and then collect it in Xiaonanhai spring group through underground runoff to overflow; Second, it is collected by surface runoff to Huan River, and the groundwater in the spring area is replenished by leakage.
Due to the interannual and intra-annual changes of precipitation, the influence on spring flow is also different. The interannual variation of precipitation, due to the regulation and storage of groundwater in the spring area, mainly affects the annual average variation of Xiaonanhai Spring, and the annual variation of precipitation leads to the annual difference of spring flow.
3. 1.2 Huan River
Huan River passes through this area for about 50km, and the water leakage from terrazzo to Xiejiaping is serious. The water leakage from Huan River is the main recharge source of spring groundwater in South China Sea. Huan River has two sources: one is descending water flow; The second is to receive backwater from Hongqi Canal and replenish groundwater in the spring area. According to the measured data of predecessors and this survey, it is speculated that the leakage of Huan River is also the main factor of spring flow in the South China Sea.
3.2 Human factors
3.2. 1 groundwater exploitation
With the social and economic development of the spring area, the amount of artificially exploited groundwater has increased year by year, especially after the 1990s, which will inevitably seize some spring flows. The South China Sea spring flow presents three steps, and correspondingly, the artificial exploitation of groundwater also presents three steps. See table 1 for specific data.
Table 1 Corresponding Table of Spring Flow and Artificial Exploitation of Groundwater
Therefore, at present, groundwater exploitation is the main controlling factor of spring water flow, and the influence of groundwater exploitation on spring water flow will become more and more serious from the development trend.
Hongqi canal water diversion
Hongqi Canal introduces turbid Zhangjiang into Linzhou. On the one hand, groundwater in the spring area is directly replenished through canal leakage and canal irrigation infiltration; On the other hand, it backwaters Huan River, and indirectly supplies groundwater through river leakage. As can be seen from Table 2, among the three platforms of spring flow, the change trend of water diversion of Hongqi Canal is also obvious.
3.2.3 Quarrying along the overflow area of the spring group will also have a certain impact on the overflow of the spring group.
4. Weight analysis of factors affecting spring flow
4. 1 Select the factors that affect the spring flow.
From the above analysis, it is not difficult to see that there are four main factors affecting the spring flow: precipitation, groundwater exploitation, water diversion in Hongqi Canal and Huan River leakage. Among them, the leakage of Huan River is mainly caused by runoff (flood) and backwater of Hongqi Canal, and it is closely related to them. Relatively speaking, Huan River leakage is only an indirect influence factor, so precipitation, groundwater exploitation and water diversion in Hongqi Canal can be used as control factors affecting spring flow.
4.2 Spring Flow Period Selection
It can be clearly seen from the table 1 that the spring flow presents three steps, corresponding to three time periods respectively, namely 1976, 1977 ~ 1989 and 1990. In order to facilitate the following calculation, the data period is selected as 1976544. See Table 2 for the data of spring flow, precipitation, artificial exploitation of groundwater and water diversion of Hongqi Canal in each period.
Table 2 Data list of each time period
4.3 Weight Analysis of Influencing Factors of Spring Flow
It is a common problem in hydrogeological analysis to apply the grey system theory to the weight analysis of influencing factors of spring flow for multivariate correlation analysis, and its purpose is to find out their advantages and disadvantages related to factors from multiple factors. When grey system theory studies the correlation between things, it takes the past and present behavior effects of things (factors) as the basis of analysis, and excavates the regularity from them. In order to judge the main factors, the variable value of "correlation degree" is put forward to determine the weight of the influence of different time and factors on spring flow.
4.3. 1 method and principle of correlation analysis
There are m sub-factors (X 1, X2, ..., Xm), which have a certain correlation with the parent factor (X0), and there are at least n dynamic observation values at the same time, and their values are abbreviated as sequences.
Parent sequence: {x0 (i)} i = 1, 2, ..., n
Subsequence: {xk (I)} k = 1, 2, …, m
i= 1，2，…，n
For comparison, it is standardized and made into:
X0 (I) and xk (I) are standardized, so there are broken lines in the t0X coordinate system, {x0 (I)}, {XL (I)}, ..., {xk (I)} ..., all of which have certain lengths on the L axis. If these multi-segment lines have a common * * * intersection (called reference point), the distance δ0k(L)= {| x0(L)-xk(L)|} between the k-th sub-line L and the bus at the same moment is the basic basis for measuring their correlation at that moment. Obviously, the smaller δ 0k (L) is, the better the correlation between the sub-line and the bus at time L. The correlation from time t=l to time t=n is expressed by the correlation coefficient:
Essays on Geology, Environment and Economics. Series 2
ξ0k(i)—— The correlation coefficient of the kth sub-line and bus x. I at the moment satisfies the value of 0≤ξ0k≤ 1, and the closer ξ0k is to 1, the better their correlation is.
Min, Δ max-The minimum and maximum values of the distance Δ 0k (i) of the mth sub-line in the interval [1, n].
Obviously, if the reference point is selected at a certain moment (1), there is δ min = 0, where δ 0k (min) = min {| x0 (i)-xk (i) |).
δ0k(max)= max { | X0(I)—Xk(I)|)
δmin = min {δ0k(min)}
δmax = max {δ0k(max)}
ξ —— positive real number, taking empirical number, whose value affects the order of [1, n] correlation coefficient at each moment. In this paper, ξ = 0.5, so the correlation between the kth sub-line in [l, n] and the bus is denoted as G0k and ∈[0, 1].
field data
According to the available data, there are three factors: the first factor is water intake from Hongqi Canal, the second factor is groundwater exploitation in spring area, and the third factor is rainfall in spring area.
Now set the matrix [xij]i= 1, 2, 3, 4.
j= 1，2，…， 13
[xij]- parent factor, spring flow over the years;
[xki]- subentry coefficient, k=2 is the annual water diversion of Hongqi Canal.
K=3 is the annual groundwater exploitation in the spring area.
K=4 is the annual rainfall in the spring area.
Calculation result
The product calculation results are shown in Table 3.
Table 3 Correlation coefficient table of each time period
Note: X2—— refers to water diversion in Hongqi Canal, X3—— refers to groundwater exploitation, and X4—— refers to precipitation.
Comprehensive analysis of the reasons for the decrease of spring flow
From the weight analysis results of the above-mentioned influencing factors of spring discharge, it can be seen that in the first phase and the second phase, the size of spring discharge is closely related to its positive related factors-precipitation and water diversion of Hongqi Canal, and the negative related factor-manual mining only takes a secondary position. Combined with Table 2, the change of spring flow in the second phase is mainly due to the increase of artificial exploitation and the decrease of water diversion.
Compared with the second phase, the precipitation in the third phase (1990 ~ 2003) is not much different. However, with the increase of artificial exploitation, the amount of water diversion in Hongqi Canal has decreased obviously, but both of them have become the main influencing factors of spring water flow in this period. Therefore, the reduction of spring water flow is an inevitable consequence. In the exploitation amount, the influence of mine drainage on the reduction of spring water inflow is more obvious.
6 conclusion
Based on the above analysis results, at present, the main reasons for the decrease of spring water flow are the increase of artificial groundwater exploitation and the decrease of water diversion in Hongqi Canal. In recent years, with the increase of artificial exploitation of groundwater, it has become the main factor affecting the spring flow.