RECHARGE OF THE SNAKE RWER PLAIN AQUIFER: TRANSITIONING FROM INCIDENTAL TO MANAGED¹

Abstract

Declining ground-water levels and spring discharges have heightened water user concerns about the sustainability of the Snake River Plain aquifer in southern Idaho. Diminished recharge from surface water irrigation and increased irrigation pumping have been depleting the aquifer at a rate of about 350,000 acre-feet/year. Previously, aquifer conditions were treated as an uncontrollable consequence of weather and development activities. With increasing competition for available water, the State appears to be progressing through a three-stage process of recharge management. The first stage is that which has occurred historically, where recharge is largely an incidental effect of surface water irrigation. The second stage is the implementation of intentional recharge with little regard to identifying or maximizing benefits. Idaho has been at this stage for the past few years. The State is entering a third stage in which recharge sites will be located and designed to meet specific water user and environmental objectives.Preliminary estimates using numerical and analytical models demonstrate that managed recharge within a few miles of the river will result in short-term increases in spring discharge. More distant recharge sites are needed to provide longer-term benefits. The primary challenge facing implementation of the managed recharge program will be the balancing of economic and environmental costs and benefits and to whom they accrue.(KEY TERMS: water management; water policy; water development; aquifer recharge; artificial recharge; managed recharge; groundwater hydrology.)The appropriation of ground water and spring flows created a dependence of water users on the incidental recharge from surface water irrigation. Incidental recharge, however, is not controlled, nor is it 'Paper No.

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“…Consider, for example, the negative impact that improvements in irrigation technology have had on the use-dependencies developed along the Snake River in southern Idaho (Johnson et al, 1999). Traditional ood-irrigation practices along the upper portion of the river were highly inef cient, which allowed a large quantity of unconsumed irrigation diversions to percolate into the upper Snake River Plain aquifer.…”

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“…For example, improved on-farm irrigation efficiency reduced pumping rates by 50%, but failed to stem the rapid decline of groundwater in the North China Plain (Kendy et al, 2003). In another example, efficiency improvements reduced irrigation diversions in the upper Snake River Plain (Idaho), but have been linked to declining ground-water levels and spring discharges in the lower portion (Johnson et al, 1999).…”

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“…And trying to remedy this lack of knowledge lasted decades (Hutchings and Petrich 2002b;Petrich and Urban 2004). As the twenty-first century dawned, IWRRI researchers reported 350,000 acre-feet annually pumped from the Snake River aquifer, an alarming amount that finally, if belatedly, pushed the state to manage recharge deliberately (Johnson et al 1999).…”