LPRV Aquifer Management: Physical Hydrology


The Bonneville gravels are extremely permeable - in places as permeable as the fractured basalt lavas of the eastern Snake Plain aquifer - and wells completed in this portion of the lower Portneuf Valley aquifer are very prolific. Water level drawdown in domestic wells pumping from the Bonneville gravel is almost unmeasurable, and municipal wells can pump 2000-3000 gallons per minute with less than 2-3 feet of drawdown.

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.