Print6.2 Aquifer Processes and Dynamics
In the first half of the module, we’ve explored the properties of aquifers. But, of course, that is only half of the story! In order for groundwater to flow, there must be a driving force. The same is true for surface water like streams or rivers: in that case, the driving force is gravity. In the case of groundwater, the driving force is a bit more complicated because it includes the combined effects of gravity and pressure.
As we will see, these driving forces are partly determined by the natural system but can be perturbed by pumping or injection in wells. When we pump water from wells, we alter the natural driving forces to move water toward the well. One important issue in aquifers is accounting for the flows in to and out of the aquifer in a groundwater budget. In extreme cases, the amount of water extracted at wells may exceed the amount introduced to the aquifer through recharge. As we’ll discuss, this tenuous condition is known as an overdraft.