Pressure moves water through pipe figure 3.36 City water systems can be considered artificial artesian systems. aquifer that is inclined so that one end is exposed at the surface, where it can receive water; and (2) aquitards both above and below the aquifer must be present to prevent the water from escaping. Such an aquifer is called a confined aquifer. When such a layer is tapped, the pressure created by the weight of the water above will force the water to rise. If there were no friction, the water in the well would rise to the
level of the water at the top of the aquifer. However, friction reduces the height of this pressure surface. The greater the distance from the recharge area (area where water enters the inclined aquifer), the greater the friction and the smaller the rise of water. In Figure 3.35, Well 1 is a no flowing artesian well, because at this location the pressure surface is below ground level. When the pressure surface is above the ground and a well is drilled into the aquifer, a flowing artesian well is created (Well 2, Figure 3.35). Artesian systems act as "natural pipelines," transmitting water from remote areas of recharge great distances to the points of discharge. In this manner, water that fell in central Wisconsin years ago is now taken from the ground and used by communities many kilometers to the south in Illinois. In South Dakota, such a system brings water from the western Black Hills eastward across the state. IN VIR1 Or GRJ On a different scale, city water systems may be considered examples of artificial artesian systems (figure 3.36). The
water tower, into which water is pumped, may be considered the area of recharge, the pipes the confined aquifer, and the faucets in homes the flowing artesian wells. J MENTAL PRC As with many of our valuable natural resources, groundwater is being exploited at an increasing rate. In some areas, overuse threatens the groundwater supply. In other places, groundwater withdrawal has caused the ground and everything resting upon it to sink. Still other localities are concerned with the possible contamination of their groundwater supply. Treating Groundwater as a Nonrenewable Resource Many natural systems tend to establish a condition of equili rium. The groundwater system is no exception. The wat table's height reflects a balance between the rate of wat added by precipitation and the rate of water removed by d charge and withdrawal. An imbalance will either raise or low the water table. A long-term drop in the water table can occui there is either a decrease in recharge due to prolonged droug
or an increase in groundwater discharge or withdrawal For many people, groundwater appears to be an en lessly renewable resource, for it is continually replenished 1 rainfall and melting snow. But in some regions, groundwal has been and continues to be treated as a nonrenewable resoui because the amount of water available to recharge the aquii is significantly less than the amount being withdrawn.
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