LPRV Aquifer Management: Physical Hydrology

Between April,1993 and September, 1994 a detailed water balance was constructed for the southern valley aquifer. Since this period comprises an above-normal and a below-normal water year, the combined results of that period is believed to closely reflect aquifer capacity during normal water years.
The figure summarizes the results for this water balance. Essentially, a water balance expresses the relationship between input (recharge), output (pumping and natural through flow), and aquifer storage changes. Note how storage was positive during the cool summer of 1993 (Day 90-300), negative during the dry summer of 1994 (Day 450-600) and close to zero for the annual normalized value covering the entire water balance period.

The residual term (Qr) in the water balance is all the unaccounted-for water, and represents the total amount of recharge originating from sources other than the Portneuf Gap. Since the river does not substantially recharge the aquifer, and no major precipitation-derived sources on the east side of the valley are known, the residual term is thought to reflect the amount of recharge originating from the southern Bannock Range.

This recharge amount is five times larger than that originating from the entire upper Portneuf - Marsh Valley watershed, and underscores the importance of local recharge in the Bannock Range to the aquifer's capacity.