Hydrogeological parameter change

1. Calculation of hydrogeological parameters in Taiyuan Basin

The selection of hydrogeological parameters directly affects the magnitude and reliability of groundwater resources calculation, so it is of great significance to study hydrogeological parameters. The hydrogeological parameters involved this time mainly include groundwater recharge coefficient of precipitation infiltration (α), phreatic water evaporation limit depth (L), evaporation intensity (ε), irrigation infiltration groundwater coefficient (β), drainage water supply (μ), hydraulic conductivity coefficient (T), elastic water storage coefficient (S), permeability coefficient (K), river leakage recharge coefficient and canal leakage recharge coefficient.

(a) Groundwater recharge coefficient of precipitation infiltration (α)

There are many factors that affect the recharge of groundwater by precipitation, including topography, lithology and structure of vadose zone, buried depth of groundwater level, precipitation characteristics and soil water content in the early stage.

Precipitation infiltration recharge coefficient is the ratio of precipitation infiltration recharge groundwater to precipitation. The annual precipitation infiltration recharge coefficient is the ratio of the sum of precipitation infiltration recharge groundwater in each period of a year to the annual total precipitation, and its expression is:

Investigation and evaluation of groundwater resources and its environmental problems in large basins of Shanxi Province

Among them: α year is the annual precipitation infiltration recharge coefficient; Pri is the recharge of precipitation infiltration, mm; P is annual precipitation, mm; N is the number of annual precipitation fields.

Calculation method of annual precipitation infiltration coefficient of long-term dynamic observation wells;

Investigation and evaluation of groundwater resources and its environmental problems in large basins of Shanxi Province

Where: μ∑δh is the sum of groundwater recharge by precipitation infiltration in each year; P year is the annual precipitation; Δ h is the rise of groundwater level caused by a certain precipitation.

According to the analysis and calculation of dynamic data, on the basis of previous experiments and considering various factors, the coefficient of groundwater recharge by precipitation infiltration in river basin is given (see chapter 4 for details).

(2) Limit depth (L) and evaporation intensity (ε) of groundwater evaporation.

The evaporation limit depth refers to the buried depth of shallow water level when evaporation stops or evaporation capacity is quite weak. Evaporation intensity is the evaporation capacity of shallow water above the limit evaporation depth per unit time.

The main factors affecting groundwater evaporation are the depth of groundwater table, the lithology of vadose zone and the evaporation intensity of water surface.

Theoretically, when the depth of groundwater level is lower than the evaporation limit depth, the dynamic curve of groundwater is almost straight without recharge and exploitation.

Limit depth of groundwater evaporation (L)

The evaporation limit depth (L) is usually calculated by iterative method, trial and error method and empirical formula, and the formula is as follows:

Iterative method:

Trial algorithm:

Empirical formula method:

Where: Δ t1and Δ t2 are calculation periods, d; H 1, buried depth of water level in the period where H2 and H3 are located, m; Z 1 and Z2 are the evaporation intensity of water surface in the time period, m/d;

According to the calculation, the evaporation limit depth of different lithology in the pore water area of Taiyuan Basin is 3.5m between sub-sand and sub-clay, 4.0m between clay silt and 4.5m between silt and clay silt.

Groundwater evaporation intensity

Calculation formula:

Where: Z0 is the evaporation intensity of liquid surface, mm/d; Δ h is the average buried depth of shallow water landing interval, mm; Z is evaporation intensity, mm/d.

From the shallow water depth map of this area (see Chapter 4 for details), it can be seen that the area with water depth less than 4m is located in Taiyuan City in the north and Pingyao and Jiexiu in the south. According to the above formula, the evaporation intensity of groundwater in Taiyuan, Pingyao and Jiexiu is shown in Table 3- 1.

Table 3- 1 evaporation intensity of groundwater in pore water area of Taiyuan basin

(3) Irrigation infiltration coefficient (β)

Refers to the ratio of the amount of groundwater supplemented by field irrigation to the total irrigation amount. There are many factors that affect irrigation infiltration coefficient, such as lithology, buried depth of water level, soil water content, irrigation quota and so on.

Calculation formula:

Where: μ is the unit output; δ h is the average elevation of groundwater level caused by irrigation, m; Q is irrigation water quantity, m3; F is the area, m2.

Three groups of irrigation infiltration experiments were arranged in Gaocun, xiaodian district City, Taiyuan City, Mazhai Village, Dongjiazhuang Town, Fenyang City and Yuci City. The surface lithology of Gaocun is silty clay, the upper part of Dongmazhai is silty clay, and the lower part is silty soil. The laboratory specific yield test results were 0. 195 and 0. 1655, respectively. There are 10 observation wells in the range of 37m×37m in Gaocun, with the buried depth of 1.2 ~ 1.3m, the cumulative irrigation water amount of 160m3 and the average water level of 100 wells of 0.19/. The buried depth of water level in Dongmazhai Village is 1.95 ~ 2.44 m, and the observation well 10 is arranged on an area of 26m×26m, with irrigation water of 60m3. The average water level of the observation well is 0.465m, and the calculated irrigation infiltration groundwater coefficient is 0.58. There are three observation wells in Yangpanbu, with water level of 5.76 ~ 6.01m, irrigation area 100m2, irrigation water volume 100m3, average water level rising height of 0.27m, and calculated irrigation infiltration coefficient of 0.039.

From the above test data, it can be seen that the irrigation infiltration coefficient varies greatly in different groundwater depth and different lithology areas. Considering various factors comprehensively, the values of irrigation infiltration groundwater coefficient are shown in Table 3-2.

Table 3-2 Irrigation Infiltration Groundwater Coefficient

(4) Elastic water storage coefficient S, hydraulic conductivity coefficient T, water supply μ and permeability coefficient K.

Hydrogeological exploration of farmland water supply has been carried out in most areas of the basin with a scale of1∶ 50,000, and a large number of single-hole and multi-hole pumping tests have been carried out. This time, five groups of pumping tests were carried out in Wenhuiyiyi and Fenyang respectively. The results calculated by the semi-logarithmic method of descent-time are as follows: the permeability coefficient of Wen Yi is t = 1983.59 ~ 265438+. The permeability coefficient k = 32. 19 ~ 35.4 m/d, and the elastic water storage coefficient s =1.79×10-3; Through the pumping test in Dongmazhai Village, Jiajiazhuang Town, Fenyang County, the permeability coefficient t = 325.84 ~ 376.5 m2/d and the permeability coefficient k = 5.65 ~ 6.53 m/d were obtained. Based on the previous work in this area, the hydrogeological parameters of shallow pore phreatic water and middle-deep pore confined water in Taiyuan Basin are given. See parameter zoning map 3- 13 and parameter zoning table 3-3 for details.

Table 3-3 Division of Confined Water in Middle and Deep Pores and phreatic water parameters in Shallow Pores in Taiyuan Basin

Fig. 3- 13 Taiyuan basin parameter calculation zoning map

2. Calculation of hydrogeological parameters in Datong Basin

From the shallow water depth map of this area in 2004, it can be seen that the areas with water depth less than 4m are mainly distributed in the alluvial plain in the middle of the basin, and Huairen, Yin Shan, Yingxian and Shuozhou in the south of the basin have large distribution areas. According to the calculation and previous test data, the determined value of evaporation intensity in this area is shown in the following table (Table 3-4).

Table 3-4 Groundwater Evaporation Intensity in Pore Water Area of Datong Basin

According to the experimental data of irrigation infiltration collected in the Report on Water Resources Evaluation and Balance between Supply and Demand in Tongyan Small Economic Zone of Shaanxi Province, the irrigation infiltration coefficients with different water levels, different lithology and different irrigation quotas are obtained. See Table 3-5 for the values of irrigation infiltration coefficient.

Hydrogeological exploration of farmland water supply with the scale of1/50,000 has been carried out in most areas of the basin, and a large number of single-hole and multi-hole pumping tests have been carried out. In this work, 1 17 pumping test holes were collected in this area. Six groups of pumping tests were carried out in Dangliuzhuang Township, Jinshatan Town, Xinfa Village, Yulin Village, Zhangzhuang Township, Shanyin County and Shaleng Township, Shuozhou City respectively. The concrete situation of the pumping hole is calculated by AquiferTest program and unsteady flow method.

Table 3-5 Irrigation Infiltration Groundwater Coefficient

Table 3-6 Statistics of this pumping test in Datong Basin

Table 3-7 Calculation Results of this Pumping Test in Datong Basin

Based on the previous work in this area, the hydrogeological parameters of shallow pore phreatic water and middle-deep pore confined water in Datong Basin are given. See figure 3- 14, figure 3- 15, table 3-8 and table 3-9 for details.

Figure 3- 14 Partition Map of Precipitation Infiltration Coefficient in Datong Basin

Figure 3- 15 Partition Map of Pore Water Parameters in Middle and Shallow Layers of Datong Basin

Table 3-8 Zoning Table of Shallow Pore Groundwater Parameters in Datong Basin

sequential

Table 3-9 Parameter Zoning of Confined Water in Middle and Deep Pores of Datong Basin

Three. Xinzhou basin

Xinzhou basin is rich in groundwater resources and has excellent mining conditions. Before 1970s, the scale of groundwater exploitation was small. From the early 1970s to the late 1980s, with the popularization of agricultural irrigation, the development of industrial production and the expansion of urban scale, the amount of groundwater exploitation increased rapidly. The mining object is mainly shallow water, which leads to the general decline of shallow water level (but the decline is not large). Since 1990s, although the amount of groundwater exploitation has been increasing year by year, the increase rate is small, and the number of middle-level wells is gradually increasing, forming a new mode of mixed exploitation of shallow water and middle-level water, and the groundwater level is in a state of dynamic balance. Influenced by the artificial exploitation of groundwater, the hydrogeological parameters such as precipitation infiltration coefficient and hydraulic conductivity coefficient have changed to some extent.

The variation of precipitation infiltration coefficient in this area is not only related to annual precipitation and precipitation characteristics, but also closely related to the buried depth of shallow groundwater level. The existing data show that in the piedmont inclined plain area, the shallow water level is generally above 7m, and the precipitation infiltration coefficient is reduced to varying degrees due to the drop of water level. In the alluvial plain area, the shallow water level is generally less than 7m, and the drop of water level leads to the increase of precipitation infiltration coefficient. See Chapter 5 for the variation of precipitation infiltration coefficient of different geomorphic units.

Since 1970s, the hydraulic conductivity of aquifers in this area has obviously decreased, which is mainly reflected in the decrease of shallow groundwater level, the upper part of shallow aquifers is in a state of drainage, and the thickness of aquifers is reduced, which directly leads to the decrease of hydraulic conductivity. Because of the different degree of shallow water level decline, the degree of permeability coefficient decline is also different. According to the analysis of borehole data near the calculation section of groundwater lateral recharge, the aquifer thickness is generally reduced by 3 ~ 6m, and the hydraulic conductivity is reduced from 60 ~ 250m2/d in the mid-1970s to about 50 ~ 200m2/d at present.

The specific yield in Xinzhou Basin is comprehensively determined according to the lithology, classification and water abundance of aquifers in different geomorphic units. See table 3- 10 and figure 3- 16.

Table 3- 10 specific yield Division of Shallow Aquifer in Xinzhou Basin

Figure 3- 16 specific yield Zoning Map of Xinzhou Basin

Four. Linfen basin

After collecting previous data, investigation and calculation, the precipitation infiltration coefficient of Linfen Basin is determined as shown in Table 3- 1 1. See fig. 3- 17 and table 3- 12 for the permeability coefficient and specific yield zoning of Linfen basin.

Table 3- Statistical Table of Precipitation Infiltration Coefficient in Plain Area of Linfen Basin +0 1

Fig. 3- 17 permeability coefficient and specific yield zoning map of the study area

Table 3- 12 Parameter Zoning Table of Linfen Basin

V Yuncheng basin

The long-term observation network of groundwater in Yuncheng basin has been established for a long time, and a large number of monitoring data of groundwater level have been accumulated. After many geological and hydrogeological investigations and groundwater resources evaluation, a large number of precipitation infiltration values have been obtained. Referring to the previous comprehensive results, combined with the current vadose zone lithology and the buried depth of groundwater table, the recharge coefficient of precipitation infiltration in Yuncheng Basin is given, as shown in Table 3- 13.

Table 3- 13 Statistics of Precipitation Infiltration Coefficient in Plain Area of Yuncheng Basin

The effective utilization coefficient of canal system is not only affected by lithology and groundwater depth, but also related to the lining degree of canal. The correction coefficient R is the ratio of the actual infiltration recharge of groundwater to the loss of water in the canal system Q, and it is a parameter reflecting the loss of evapotranspiration consumed by the canal during water conveyance, which is influenced by factors such as canal water conveyance time, soil quality of the canal bed, presence or absence of lining and buried depth of groundwater. Generally, it is obtained by channel water discharge test. This evaluation mainly refers to the relevant test results of Yuncheng Water Resources Bureau, as shown in Table 3- 14.

Table 3- 14 Statistics of η, r and m values in irrigation areas over 10,000 mu in Yuncheng Basin

The β value of irrigation regression recharge coefficient is related to lithology, vegetation, groundwater depth and irrigation quota, which is generally obtained by irrigation infiltration test. This evaluation is mainly determined by referring to the data of Yuncheng water conservancy department. See table 3- 15 for details.

Table 3- 15 β value of irrigation regression coefficient in Yuncheng basin

River seepage recharge coefficient is the ratio of groundwater recharge by river seepage to river inflow. Its value is related to lithology, flow rate, buried depth of groundwater level and length of river bed leakage section. There are many seasonal rivers along Zhongtiaoshan in Yuncheng Basin, and the underlying surface of the riverbed is mainly gravel. In flood season and rainy season, the water level of the surface river bed is much higher than the groundwater level, which creates very convenient conditions for the infiltration of surface water. According to the river leakage data, the following mathematical model can be established:

Investigation and evaluation of groundwater resources and its environmental problems in large basins of Shanxi Province

Where: M River is the river leakage recharge coefficient; A is the calculation coefficient, a = (1-λ) × (1-φ) L, and φ is the loss rate per kilometer; L is the leakage length of the river, and km and q are the inflow of the river, m3/s.

According to the research results of Yuncheng water conservancy department, A value is about 0.090.

The permeability coefficient of aquifer is mainly obtained by field pumping test through the calculation formulas of steady flow and unsteady flow. Various exploration departments have carried out various investigations in Yuncheng basin, carried out a large number of pumping tests and accumulated rich data. According to the results of this pumping test, the above parameters are revised, and the results are shown in Table 3- 16.

Table 3- 16 Selection Table of K Value of Loose Rock in Yuncheng Basin

Under the same lithology and rainfall, with the increase of groundwater depth, the rainfall infiltration recharge coefficient will reach the maximum, and then tend to decrease or tend to be constant. Emei platform and Wenxi platform in the north of Yuncheng basin are deeply buried, and the surface is mainly loess. Precipitation infiltration mainly depends on vertical joints and cracks of loess and "flowing sea cracks" injected into the ground in the form of "piston" For many years, the infiltration coefficient of precipitation has remained basically unchanged, and it is 0. 108 ~ 0. 16538 calculated by dynamic analysis. In the lake plain area in the middle of the basin, the surface lithology is mainly composed of clay silt, loam and silt of QP3+QH alluvial lake facies. Due to intense mining, the regional water level drops seriously, and the surface is saturated within several meters to tens of meters, which provides storage space for precipitation infiltration and strengthens the transformation of precipitation into groundwater. According to the long-term observation data of groundwater and secondary rainfall data, the lake plain area of the basin is calculated, and the precipitation infiltration coefficient is between 0. 1 ~ 0. 162, and the upstream is larger than the downstream in general. In the eastern and southern piedmont inclined plain areas, the buried depth of groundwater level is generally more than 5m, even tens of meters, and the surface lithology is mostly clay silt and loam, especially near some gullies, which are dry gravel within tens of meters from the surface. Generally, rainfall basically does not produce surface runoff, which undoubtedly increases the transformation of precipitation. According to relevant data, the infiltration coefficient of precipitation is as high as 0.2 1 ~ 0.30. Because the previous work is not systematic, there is no systematic classification of rainfall infiltration coefficient, which is not convenient for comparison. However, judging from the changes of lithology and groundwater in the saturated zone of Yuncheng Basin, the rainfall infiltration coefficient in other areas has undoubtedly increased except Emei tableland and loess hilly area.

The aquifers of pumping wells in the basin are mostly composed of several aquifers. According to the calculated value of this pumping, the K value in previous research results is revised, and the permeability coefficient of each geomorphic unit in Yuncheng Basin is obtained. Generally speaking, the maximum value of K is11.3 ~14.6 m/d, followed by the slope plain in front of Zhongtiaoshan Mountain, which is 5.45 ~ 6. 12 m/d, and the last value is Wenxi Beiyuan K =/kloc-.

Yuncheng Basin is divided into 10 parameter area according to landform unit, aquifer lithology, groundwater hydraulic characteristics and various parameter characteristics, as shown in Table 3- 17 and Figure 3- 18.

Table 3- 17 Hydrogeological Parameter Zoning of Yuncheng Basin

The intransitive verb Changzhi basin

According to the hydrogeological conditions, the parameter zoning of Changzhi Basin is shown in Figure 3- 19 and Table 3- 18.

Figure 3- 18 Hydrogeological Parameter Zoning Table of Yuncheng Basin

Figure 3- 19 Parameter Zoning Map of Changzhi Basin

Table 3- 18 Parameter Zoning of Shallow Pore Groundwater in Changzhi Basin

(A) the precipitation infiltration recharge coefficient changes

According to the research results of Taiyuan Groundwater Resources Evaluation Report, the precipitation infiltration coefficient of clay silt, extremely fine sand and fine sand in the basin increases with the increase of groundwater depth, and when the local groundwater depth exceeds a certain value, the precipitation infiltration coefficient begins to stabilize; Under the same lithology and groundwater depth, the greater the precipitation, the greater the precipitation infiltration coefficient. For clay silt, extremely fine sand and fine sand, the precipitation infiltration coefficient of fine sand is >: extremely fine sand > clay silt. Generally speaking, the coarser the particles, the greater the precipitation infiltration coefficient.

With the change of precipitation, unsaturated zone plays a regulating role in the process of groundwater recharge by precipitation infiltration, which lags behind the precipitation process. The length and characteristics of its lag time are closely related to the gravity water storage capacity of vadose zone. The deeper the groundwater is buried, the greater its storage capacity, the stronger its regulation ability and the more obvious its lag phenomenon.

Among clay silt, extremely fine sand and fine sand, when the precipitation is equal, the order of precipitation infiltration coefficient from large to small is fine sand, extremely fine sand and clay silt. The influence of precipitation shows that α times first increases with the increase of precipitation, and when the precipitation exceeds a certain value, α times decreases, which is the best precipitation. α years have the same regularity as α times, and from the analysis of infiltration mechanism, α years also have the best annual precipitation.

When the local groundwater depth is zero, the recharge coefficient of precipitation infiltration is also zero, and then it changes from small to large with the increase of groundwater depth. When the local groundwater depth reaches a certain value, the recharge coefficient of precipitation infiltration reaches the maximum, that is, the optimal recharge coefficient of precipitation infiltration, and then decreases from large to small with the increase of groundwater depth, and tends to a fixed value when it reaches a certain depth. The influence of groundwater depth on the recharge coefficient of precipitation infiltration can be explained from three aspects.

Buried depth reflects the size of water storage. When the buried depth is zero, the storage capacity is zero. At this time, no matter how much precipitation, there is no possibility of infiltration recharge. When the buried depth increases, the underground reservoir is replenished by precipitation infiltration. At this time, the recharge coefficient of precipitation infiltration is greater than zero, and it increases with the increase of buried depth. When the local groundwater reaches the optimal depth, its corresponding precipitation infiltration recharge coefficient is the optimal precipitation infiltration recharge coefficient, because in the same area, there must be a maximum infiltration recharge with the change of groundwater depth due to the precipitation sequence. When the local groundwater depth is small, the groundwater storage capacity is small, resulting in full storage and runoff production, which can not make all precipitation seep; When the local groundwater depth increases again, the loss is greater than the optimal groundwater depth, so the recharge coefficient of precipitation infiltration decreases with the increase of groundwater depth. For different grades of precipitation, the depth of groundwater table where the maximum value of α appears is also different. The optimum burial depth is related to lithology and rainfall.

The buried depth of groundwater reflects the amount of soil moisture to some extent. The vertical distribution of soil moisture can be roughly summarized into three situations. 1 The situation is that the groundwater depth is small, and the capillary rising water can always reach the surface; In the second case, when the local groundwater depth is large, the capillary rising water cannot reach the surface; In the third case, the groundwater depth is between the two. Due to the fluctuation of groundwater level, capillary rising water sometimes reaches the surface, and sometimes it does not reach the surface. These three conditions will have different effects on precipitation infiltration recharge. In the case of 1, the water can move down rapidly through the capillary under the action of gravity at the beginning of precipitation, and the groundwater level will rise rapidly after the beginning of precipitation. In the second case, precipitation must first meet the needs of soil water shortage, and then recharge groundwater through gaps under the action of gravity. The leakage path is longer than that of 1, and the infiltration mode is different.

Figure 3-20 Relationship between Permeability Coefficient and Depth

Influence of different groundwater table depths on recharge coefficient of precipitation infiltration. The maximum depth of water potential energy experiment in Taigu balance experimental field in the basin is 8.2m, and the observation point is 4 1. The analysis results of many years' data show that the change of soil water potential energy can be divided into three change areas from bottom to top-drastic change area, alternating change area and stable area. The buried depth of the abrupt zone is 0 ~ 1. 1m, and the change of soil water potential energy is more than 200× 133 Pa. The buried depth of the alternate zone is 1. 1 ~ 3.6m, and the range of soil water potential energy is greater than (100 ~ 200) × 133 Pa. The buried depth below 3.6m is a stable zone, and the change of soil water potential energy is less than 100× 133Pa, especially when the buried depth is below 4.5~5.0m, and the change of soil water potential energy is generally less than 50× 133Pa, so the soil water is in infiltration state all the year round. The results show that when the buried depth is less than 5.0m, the infiltration recharge is stable, indicating that with the increase of buried depth, the precipitation infiltration recharge coefficient will tend to be stable. Therefore, when the buried depth is greater than 5.0m, the annual value of α can be fixed and will not change with the buried depth. The reason is that the buried depth of groundwater has reached or exceeded the limit buried depth of groundwater, the loss tends to be constant, and the water does not move upward, so it will inevitably move downward, thus forming a stable precipitation infiltration recharge coefficient value that varies with the buried depth of groundwater.

(2) the change of permeability coefficient

The permeability of porous water-bearing media depends not only on particle size, particle gradation and cementation degree, but also on its buried depth. With the increase of depth, porous water-bearing media with the same lithology will be compacted and the permeability coefficient will decrease.

According to the statistics of hundreds of borehole data in the top area of alluvial-diluvial fan in the piedmont of Hebei Plain, the permeability coefficient of various water-bearing media decreases exponentially with the increase of buried depth, and the variation law of permeability coefficient of some deep layers and different lithology with buried depth refers to the following empirical formula:

When the lithology is gravel, the relationship between permeability coefficient and buried depth is as follows:

k = K0e-0.0 13 1h R = 0.877

When the lithology is gravel, the relationship between permeability coefficient and buried depth is as follows:

k = K0e-0.0 1 16h R = 0.869

When the lithology is medium-coarse sand, the relationship between permeability coefficient and buried depth is as follows:

K=K0e-0.0057h R=0.896

K is the permeability coefficient of buried depth; K0 is the permeability coefficient of shallow surface layer; H is buried depth; R is the correlation coefficient.

Therefore, for the same lithology, its permeability coefficient is related to depth (Figure 3-20).