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Below Hailey the Valley widens out substantially, becoming a drier, more agricultural landscape. This warmer lower section of the watershed collects only about 220,000 af of precipitation from 255 square miles. In the research year, which long-term (80-year) river flow averages would suggest was unrepresentatively wet, precipitation plus upper valley contribution totaled 612,000 af, of which 161,000 was consumed by evapotranspiration, 107,000 by crop irrigation and less than 1,000 by residential use. Of the remaining 343,000 af that flowed out of the valley that year, only two-thirds left by way of the Big Wood River. The balance, representing underflow and seepage from irrigation canals and the river, first gathered in the aquifer and then either continued underground or surfaced through springs, before exiting the watershed at Picabo.

I did some math. Projecting a valley population of 50,000 (a possible total build-out figure, although the latest tally is not even 20,000) and a per capita water usage rate of 1,000 gallons per day (twice as much as current local averages and almost 6 times the national average), the human demand on the valley's watershed would be 56,000 af, but as much as 85 percent of this amount would be returned to the system. A corresponding increase in landscape irrigation could account for another 77,000 af, and only half of this would actually be consumed.

So, even assuming a bias in the research year and an explosion in population and water usage, the numbers by themselves seem to make a case that the Big Wood River watershed is a healthy, well-endowed, and accommodating water resource system. But as Dr. Brown reminds us, "Science tends to be weakest at extremes. It's much better at measuring and understanding the mid-range, the close-at-hand rather than the distant."

One such "extreme" occurred in June 1992 and was the catalyst that initiated the seven-year study. After several years of dry weather conditions and below-normal river flows, Silver Creek started suffering from reduced levels of dissolved oxygen. In one day, fifty large trout died. The same low dissolved-oxygen levels recurred last summer and caused stream managers to request a voluntary curtailment of fishing. These episodes can be considered "extreme;" or they can be taken as warning signs that the watershed is not as robust as the numbers suggest.

Perhaps more alarming is an indication that the delicate nature of the system extends beyond mere volume fluctuations. Recent reported instances of contaminated wells have exposed a potential problem in water quality, particularly in certain parts of the unincorporated county. Water quality issues will not only catch the eye of local health officials and county commissioners; they will attract the attention of the state.

In 1981, the state of Idaho designated the whole of the Big Wood River, from Titus Lake to Magic Reservoir, a Special Resource River. This means it is recognized by the state as "needing intensive protection," and it falls to the state Department of Environmental Quality to monitor its condition and implement policy. Part of this policy is to disallow any "new point source" that by reason of its discharge "can or will result in a reduction of the ambient water quality" as measured immediately below the discharge zone. The practical implication of the policy is that no new wastewater treatment facility, except where it replaces existing capacity, can be built. Nor can existing capacity be expanded. Consequently, any increased population growth will require alternative wastewater management applications, and these will probably interact, as septic systems do now, with the ground water.

Analyzing any dynamic system from a fixed perspective in time invites problems. This is particularly true when the system, such as a watershed, contains components that can neither be seen nor definitively measured, such as ground water and the aquifer. It seems important, therefore, to take great care before drawing conclusions from the Big Wood study. (For instance, in the above projection of a build-out scenario, the net consumption of water seems comfortably within the resource's tolerances, but in fact, unless recent practices change, almost all of the increased demand would be for ground water, of which there most likely would not be enough.)

The challenge facing County planners and citizens alike is to assess the impact of each new, expanded, or changed water use with the awareness that the next development or septic system or water right transfer or land use change or riverside encroachment has the potential to permanently impair a fragile system. Normally, the temptation is to embrace generalities and dismiss anomalies. But it is the anomalies, the extremes, that may have the greatest implications for the future of the Big Wood River watershed. Just like the dripping of melting snow in the middle of a winter night, they command one's attention.


Brought up and educated in New England, and professionalized in New York City, Bill Lowe came here in 1982 to raise a family and spend more time with his sense of humor. Currently, he’s promoting a new circuit-board technology based on vector logic.



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