When an aquifer is sandwiched by two parallel boundaries, it is called a banded aquifer. In this condition, when applying the mapping method, the mapping should appear an infinite number of times. In this way, one well in the aquifer becomes an infinite row of wells in the infinite aquifer after being mapped an infinite number of times (3-5 times is enough in real work) (Figure 5-7).
Figure 5-7 Pumping wells near two parallel supply boundaries
1 – actual pumping well; 2 – virtual pumping well 3 – virtual water injection well;
Depending on the needs of working practice, only a brief analysis of the steady flow is provided here.
1. When the well is not located in the middle of the aquifer
The distribution of wells is shown in Figure 5-7. By applying the principle of superposition, the drawdown depth at any point A (x, y) can be obtainedas:
Groundwater dynamics
In the formula: l is the width of the aquifer strip, i.e. both The vertical distance between the parallel boundaries a is the distance between the real well and the vertical axis. Move point A towards the well wall (x=a-rw; y=0) to obtain:
1) Well flow in pressure wells
Water dynamics groundwater
2) Flow rate of phreatic wells
Groundwater dynamics
2 When the well is located in the center of the strip aquifer
Equation (5- 36. ) and equation (5-37) can be simplified. If both limits are recharge limits, the confined aquifer well flow formula is:
Groundwater Dynamics
Summary
The Skill is required to study through this chapter. conditions for applying the well flow equation in phreatic aquifers and confined aquifers near the water supply limitwater in a straight line (isolated), such as equation (5-3), equation (5-4), equation (5-7), equation (5-8), formula (5- 10), formula (5-12), formula (5-17), formula (5-18), etc. Then, in production practice, correct analysis and evaluation can be carried out based on specific situations.
1. What do you think are the main characteristics of a virtual well when using the mirror method principle to solve the well flow problem near the boundary?
2. How do you understand that the fan angle (θ) of a fan-shaped aquifer must be divisible by 360°?
3. Are the properties of virtual wells determined to be the same for quadrant aquifers and fan-shaped aquifers?
Exercises
1. It is known that a submersible well located near the water supply boundary in a straight line pumps water at a stable rate, as monFigure 5-8. The thickness of the natural water table before pumping is H0 = 30 m, the drop in water level in the pumping well is sw = 5 m, the radius of influence R = 50 m, the radius of the pumping well rw = 0.25 m, the distance between the pumping points hole and the boundary a = 10 m, and the permeability coefficient of the aquifer K = 3 m/ d. Find the stable flow rate (Q) of the pumping well?
Figure 5-8 Pumping water from wells near the water supply limit in a straight line
2 It is known that a single complete well located in a Aquifer confined in quadrant is used for pumping. water at a constant flow and stable flow, as shown in Figure 5-9. Among them: a=10m, b=5m, K=4m/d, sw=10m, aquifer thickness M=20m, shadowThe sound radius R=30m and the pumping well radius rw=0.20m What is the stable flow rate (Q) of the well?
Figure 5-9 Schematic diagram of pumping water from the quadrant aquifer
A power plant of sWater storage uses excess electrical energy to drive water pumps to pump water from the lower level. tank during the period of low power consumption. Access the upper tank and store it. During the peak electricity consumption period, the water stored in the upper reservoir is released to drive the generator to produce electricity, and the water returns to the lower reservoir.
In the process of using electricity to drive a water pump to pump water and then releasing the water to produce electricity , due to the existence of friction and resistance, part of the energy must be converted into internal energy and lost. Therefore, ultimately, the electricity generated is less than the electricity consumed to pump the water. However, for hydroelectric power plants, the advantages far outweigh the disadvantages.
QuantWhen asked about the subject, it is not very clear. If it is a question of storing excess electrical energy, there is of course no explanation. If other energy is used to run the pump to pump water, and the water is then used to generate electricity, it is somewhat superfluous and the gain exceeds the loss. For example, if you use gasoline, it is better to directly use a gasoline engine to drive a generator to generate electricity, which is more direct, less troublesome and more energy efficient.
Seeing such a question, even if the person asking the question wants to work hard to find out the truth, this approach is still a stupid method of "taking off your pants and farting - useless".
My hometown is on a thousand-meter-high mountain. Because there is a sinkhole (we call it a hot tub), the whole mountain is empty, so of course there. Hethere is no sinkhole, it is natural mountain spring water. Therefore, water for humans and livestock depends on several large artificially dug ponds. The ponds are filled with heavy rains in summer, but there are no draft problems. , in the event of a long drought in spring and summer next year, pond water cannot be connected, and drinking water for people and livestock will become a big problem. I remember once there was no water supply in the entire mountain. People and animals went to the foot of the mountain to drink water, but they had to carry water on their shoulders and backs. there wasn't much water under the mountain. Ultimately, the county used fire trucks to supply water. To meet urgent needs.
The village leaders finally decided to build a reservoir on the mountain et to pump water from the bottom of the mountain to the top. To this end, men, women and children are at the top. mountain mobilized together, raised funds and volunteered to lift the power poles. We installed cables to provide electricity, built two pumping stations and dug a pumping well at the foot of the mountain. Finally, we used a three-stage pumping station. relay method to send water to the first reservoir at the top of the mountain, then used The action of gravity and no power sends the water to the second reservoir (the second top of the hill), and so on, through the mountains and ridges before reaching the pond.
Judging from reality, suppose the water is pumped up the mountain, and then the water from the mountain is used to produce electricity——
First, sIf we want to produce electricity continuously, we must have a constant flow of water. How big should the mountain reservoir be?
Second, the water in the reservoir is water without a source. Is it necessary to continually pump water up the mountain to solve the electricity problem?? Rather than doing this, it is better to directly use the electricity or fuel used to pump water or generate electricity.
Third, assuming that the cost of pumping water up the mountain is much higher than the cost of generating electricity, the gain exceeds the loss. Is there such a fool in the world? ?
In my opinion, there is no such designer or leader in the world, it's just for fun!
April 6, 2021 4:27 p.m.