|This graph is an example of the kind of
information that water managers use to determine the permeability of the aquifer around a
well, and the capacity of a well. It shows how drawdown varies with the logarithm of time
after this well is turned on. The aquifer here is so permeable that when this well begins
pumping at 2000 gallons per minute, the water table starts to 'bounce' up and down - in
effect, ringing like a bell struck. This effect is rarely seen in water wells because
aquifers are usually not so permeable as this one!
Because of this high permeability, ground water moves through
the Bonneville gravels in the southern Portneuf Valley faster than just about any other
aquifer in Idaho - up to 50 feet per day. In contrast, typical aquifers have ground water
that moves a few inches or less per day. Only the Rathdrum Prairie aquifer in northern
Idaho is as permeable and has flow rates this high. Not coincidentally, the Rathdrum
aquifer also exists in glacial flood gravels.