Snowmaking demands are small but crucial
Although snow guns crank up even during late September, if temperatures drop sufficiently, the bulk of snow is manufactured from mid-October to January. This is exactly the time of the lowest natural flow of streams. Compounding the problem is that ski areas are, almost by definition, at the highest locations of stream drainages. Tapping a stream for snowmaking can virtually deplete it.
“Snowmaking isn’t a major consumptive use,” says Alan Martellaro, water engineer for District 5, which includes Eagle and Summit counties. However, he adds, when Copper Mountain consumes water form Tenmile Creek in late fall, it is a major consumptive use of that waterway. But in terms of the annual flows of Temile Creek, it’s minor.
A study by Colorado Ski Country USA concludes that 80 percent of water used for snowmaking is returned to streams, a figure hydrologists seem to accept. But the study may miss the larger point, that of timing. Man-made snow melts in spring, when streams are already running high, and snowmaking draws the water from streams in fall, when they’re at their annual lowest flows.
Because of this problem, ski areas are increasingly looking to build small on-mountain reservoirs. The reservoirs aren’t large enough to accommodate a full season of water for snowmaking, but they do allow the ski areas to draw from the creeks more slowly, over time, spreading out the impacts. Beaver Creek has a larger on-mountain reservoir, Snowmass is building one, and Vail hopes to.