Because most landowners (farmers, cities, speculators) have the right to pump as much groundwater as they want, there is a distinct possibility that pumping on one property will reduce the water available on another property. That's because many properties may overlie a single aquifer.
The "solution" to this problem (called a common pool problem) is usually adjudication, i.e., the establishment of limited rights over water in the aquifer.* These rights may take the form of limits on the hours of pumping, total quantity pumped or exports of pumped water. The trouble is that it's hard to figure out what quantities of adjudicated water belong to each property because it's hard to know how much water is under properties and how water flows under properties (either naturally or because of withdrawals).
All of these factors get more complicated when we consider that rivers and groundwater affect each other (there are flows between them), some pumped water returns to the aquifer below (by infiltration), and laws and traditions on withdrawals are often based on use instead of sustainable supply -- a problem that's particularly nasty when someone wants to pump and export water.
So, I met a
- Yep, we know what's up.
- We have a clue +/- 10%
- We've no idea...
This is what he said:
Models can be very simple to quite complicated.Bottom Line: The science of aquifers is really tricky and really necessary for making good policies, assigning rights, etc. If we don't know what's going on, it's better to be conservative on how much water is withdrawn or how many rights are allocated.
Unfortunately, the longer I've modeled, the less I believe in it. Rather, I realize the potential for error and uncertainty.
- It depends on the aquifer system being modeled and our knowledge of it. How well we know an aquifer also depends on the location, type of aquifer, and often how deep it is? You have to drill to understand deep aquifers, but drilling is expensive.
- Does the modeler know what they are doing? (You'd be surprised.)
Can we classify aquifers? Yes, and the simpler the classification, the better. If we're not careful, we'll rape our resources and the cost for finding alternatives is expensive.
* A simpler economic method to limit overpumping is to set a tax on pumping (hp/hr) that rises if the water table falls.