(Qingdao Geological Engineering Survey Institute, Qingdao 26607 1)
Author: Wang (1956—), male, senior engineer, deputy chief engineer of Qingdao Geological Engineering Survey Institute, engaged in hydrogeology and engineering geology.
The Yellow River is a typical "suspended river" in the lower reaches of the Yellow River, which has a strong recharge effect on the shallow groundwater on both sides. The observation and test data of nine measured sections in Shandong section of the Yellow River are systematically analyzed, and the recharge relationship between the Yellow River water and groundwater and the variation law of its influence width are obtained. A one-dimensional seepage mathematical model with "dual structure" is established, and the influence width of the Yellow River water recharging shallow groundwater in this section is determined, which provides scientific geological basis for ecological environment evaluation and planning in Shandong section of the Yellow River.
Keywords: horizontal replenishment; Groundwater; Width; Lower yellow river
Introduction to 0
The Yellow River is a famous "suspended river" on the ground in the world, which is famous for its high sediment concentration, good siltation and good migration. The main stream of the Yellow River flows through 6 17km in Shandong Province, crosses 25 counties (cities) in Shandong Province, and empties into the Bohai Sea in Kenli County. The riverbed in the lower reaches of Shandong Province is 3 ~ 5m higher than the ground outside the embankments on both banks, and there is a big drop between the river water and the groundwater in the plains on both banks, which provides good hydrodynamic conditions for the Yellow River to replenish shallow groundwater. Based on the observation data of 9 sections from Yinshan to Binzhou in Dongping County, Shandong Province, the hydraulic relationship between the Yellow River water and shallow groundwater and the influence width of lateral infiltration of the Yellow River to replenish shallow groundwater are studied, which has important theoretical value and practical significance for finding out the water resources situation in this area and guiding the rational development and storage of groundwater. Determine the best development and utilization mode of groundwater, control drought, flood and saline-alkali disasters, protect the regional ecological environment, rationally utilize the water resources of the Yellow River, and harness and develop the lower reaches of the Yellow River.
According to the geological and hydrogeological conditions of Shandong section of the lower Yellow River, a hydrogeological model of "dual structure" is established, and a one-dimensional seepage mathematical model of "dual structure" is further analyzed and established. Using this model and groundwater dynamic data, the influence width of lateral seepage of the Yellow River to replenish shallow groundwater is determined.
1 establishment of hydrogeological model for lateral seepage recharge of shallow groundwater in the yellow river
On the basis of analyzing the stratum structure, lithology, aquifer burial conditions and distribution law of each experimental reach in the area, the study area is generalized as a "dual structure" porous media seepage model (Figure 1).
As can be seen from Figure 1, the middle part of the model is medium-fine sand or silty sand, which constitutes an aquifer and has the characteristics of micro confined water. The upper part is mainly fine clayey silt and loam with loose structure, which constitutes weak aquifer (phreatic water) and vadose zone; The lower part is a dense loam and clay layer, which constitutes a water-resisting layer.
Figure 1 Schematic Diagram of Porous Media Seepage Model with "Double Structure"
According to the nature of the undercurrent of the Yellow River cutting, the groundwater seepage in such a group of heterogeneous and anisotropic porous media aquifers is an incomplete and semi-bounded seepage, and the side near the river is the recharge boundary with the Yellow River water as the recharge source, showing the runoff condition that the distance between groundwater and the Yellow River is approximately parallel. The top is the water level dividing line; The bottom is a waterproof border. Therefore, the lateral seepage of the shallow groundwater system supplemented by the Yellow River can be solved by one-dimensional seepage.
2. Establishment of one-dimensional seepage mathematical model of "binary structure"
Through the analysis of groundwater dynamics, recharge, runoff and discharge conditions in this area, it is found that the water level of the Yellow River is one of the main factors to control the groundwater level, and the groundwater level changes accordingly with the change of the water level of the Yellow River. One-dimensional unsteady seepage of "binary structure" can be expressed by the following set of mathematical relations:
Shandong environmental geology collection
When t = 0
h 1(x，0)=h 1，h2(x，0)=h2 (2)
When t > 0
h 1(0，t)= h0+vδt，h2(∞，t)=h2 (3)
Where T2 is the permeability coefficient of the slightly confined aquifer; H 1 and h2 are the groundwater levels at the beginning and end of the cycle, respectively; K 1 and k2 are the permeability coefficients of phreatic water and weakly confined aquifer, respectively; M 1 and m2 are the thickness of phreatic water and slightly confined aquifer, respectively; Is the water storage coefficient of micro confined aquifer; X is the horizontal distance from the calculation point to the waterline of the Yellow River; T is the calculation time; V is the water level change rate of the Yellow River; Δ t is the calculation period length.
For the solution of formula (1) under initial condition (2) and boundary condition (3), when the time is long:
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Where: μ 1 is the water supply of the phreatic aquifer; A is the permeability coefficient of micro confined aquifer; η is a variable determined by Formula (5); Other symbols have the same meanings as before.
The final seepage flow for recharging shallow groundwater by lateral seepage of Yellow River water is as follows:
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Where q0 is the final seepage flow of Yellow River water at x = 0 when shallow groundwater is replenished by lateral seepage; Qx is the final seepage flow during the lateral infiltration of the Yellow River water into the shallow groundwater at the distance from the Yellow River X; Other symbols have the same meanings as before.
The total amount of shallow groundwater replenished by lateral seepage of the Yellow River in time δ t is:
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Where Q0 is x = 0, the total amount of shallow groundwater replenished by lateral seepage of the Yellow River in time δ t; Qx is the total amount of shallow groundwater replenished by lateral seepage of the Yellow River during the δ t period from X to the Yellow River; Other symbols have the same meanings as before.
at)
The correlation function is called the influence coefficient, which can be obtained by looking up the table.
As a special case of unsteady seepage, the solution (1) gives a special solution of one-dimensional "double structure" stable seepage when the water level of the Yellow River changes little and is basically stable at h0:
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The lateral seepage of the Yellow River can supplement the steady seepage of shallow groundwater, which can be solved by Darcy formula:
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Where: j is the hydraulic gradient; B is the calculated section width; L is the horizontal distance from the calculation point to the waterline of the Yellow River; Other symbols have the same meanings as before, as shown in Figure 2.
Fig. 2 schematic diagram of symbolic meaning of one-dimensional seepage mathematical model with "double structure"
3 Analysis and determination of replenishment impact width
3. 1 Determination of hydrogeological parameters
3. 1. 1 Determination of hydrogeological parameters based on pumping test data of unsteady flow.
Hydrogeological parameters are calculated according to the pumping test data of unsteady flow in each section. See table 1 for relevant hydrogeological parameters.
Table 1 Hydrogeological Parameter Table
3. 1.2 Verification of hydrogeological parameters with dynamic data of groundwater level
Select the dynamic data of groundwater level from1988 65438+February 2 1 to 65438+February 0989 1 (including 42 days) and calculate with formula (4). The results are shown in Table 2.
Table 2 Calculation of Aquifer Permeability Coefficient Based on Dynamic Data of Water Level
It can be seen from table 1 and table 2 that the values of a calculated by the two methods are close, which shows that the selected parameters and the established one-dimensional seepage mathematical model with "double structure" are reasonable.
3.2 Determination of replenishment influence width
3.2. 1 groundwater permeability curve method
3.2. 1. 1 day permeability curve method
Using the observation data of each section on a certain day in August 1988, the infiltration curve of shallow groundwater is made, and the recharge influence width of each section is explained according to the infiltration curve, as shown in Table 3.
Table 3 Determination of recharge influence width by daily infiltration curve method
3.2. 1.2 year water level permeability curve method
According to the observation data of 1988 in dry season, normal season and wet season, the groundwater infiltration curves of each section are made respectively, and then the recharge influence width of each section is explained according to the infiltration curves, as shown in Table 4.
Table 4 List of recharge influence width determined by four-year infiltration curve method
3.2.2 Dynamic type analysis method
According to the observation data of 1988 and 1989 in February, the water level duration curve of each hole, precipitation evaporation duration curve and shallow groundwater level duration curve are made respectively, and then the dynamic types are analyzed to determine the influence width of the Yellow River recharge in each section, as shown in Table 5.
Table 5 Determination of Influence Width of Yellow River Replenishment by Dynamic Type Analysis
3.2.3 Calculation Method of Unsteady Flow
According to the analytical solution (4) of one-dimensional unsteady seepage, the sweep range of the Yellow River water when it changes from low water level to high water level in one year is calculated.
Taking Jiaomiao section of Qihe River as an example, the detailed calculation shows that the calculation methods of other sections are the same.
When the groundwater level change (h2-h0) under the influence of the Yellow River water level change (Vδ T) is less than 5‰, it is considered that the groundwater level there is unchanged, and its distance to the Yellow River is called the influence range.
According to formula (4), the influence coefficient (v δ t) = 0.005.
From the lookup table:
According to table 1, a =153272.73m2/d.
The analysis of the water level curve at Luokou Station of the Yellow River shows that the time from the lowest value to the highest value is 43 days, that is, t = 43d and x = 8256.25m ..
It is basically close to the value determined by the above method, and the error is only 8.27%. Therefore, this method is an effective one.
3.2.4 Grey relational analysis method
Within the recharge range of lateral infiltration of the Yellow River, the recharge of shallow groundwater is mainly atmospheric precipitation infiltration and lateral infiltration of the Yellow River, and its water quality is controlled by atmospheric precipitation and water quality of the Yellow River. Their proportions are different, but the chemical composition of shallow groundwater is different. Based on this, it is a feasible method to determine the proportion of Yellow River water in shallow groundwater by grey theory correlation analysis. This time, it's only the part of King Qihe.
3.2.4. 1 calculation data
According to 9 precipitation water quality analysis data of Jinan Environmental Hydrogeological Station 1988 and 1989, the average value is taken as precipitation water quality data; 1989 May Yellow River water quality analysis data (location), which is the Yellow River water quality data; 1July, 989, the complete analysis data of shallow groundwater in each hole of this site was taken as the water quality data of shallow groundwater in each hole.
3.2.4.2 calculation steps
Firstly, the analysis results of 15 analysis items are averaged from the water quality data, and then the absolute difference, maximum and minimum difference, correlation series and correlation coefficient are calculated. Finally, the replenishment rate is calculated (see Table 6).
Table 6 Summary of Supplementary Rate Calculation Results
Note: Calculation formula:
Determination of Influence Width of 3.2.4.3 Replenishment
Because the water quality of shallow groundwater is also influenced by human economic activities, evaporation, concentration and other factors, and the Yellow River has been affected by it for more than 140 years, combined with the above methods, the influence width of lateral seepage recharge of the Yellow River in Dawang section of Qihe River is determined to be 7 ~ 9 km.
5 conclusion
On the basis of studying the geological and hydrogeological conditions on both sides of the Shandong section of the lower Yellow River and establishing a one-dimensional seepage mathematical model of "dual structure", based on the experimental observation data of nine sections perpendicular to the Yellow River, the influence width of lateral seepage of the Yellow River on shallow groundwater recharge is studied by using five methods, including daily infiltration curve method, annual water level infiltration curve method, dynamic type analysis method, unsteady flow calculation method and grey correlation analysis method. It is concluded that the influence width of Yellow River water on groundwater lateral seepage recharge is 7 ~ 9 km upstream (above Jiyang) and 3 ~ 5 km downstream (below Jiyang), which decreases gradually from upstream to downstream, and the north bank is smaller than the south bank. This conclusion can be used as the basis for the evaluation, development and protection of groundwater resources along the Yellow River.
refer to
Research group of hydrogeological engineering geological methods of Ministry of Geology and Mineral Resources. Handbook of hydrogeology. Beijing: Geological Publishing House.
Shen et al. 1985. Hydrogeology. Beijing: Science Press.