Brief by Central Staff
Water – June 2004 – Colorado Central Magazine
Glen Canyon Dam and its associated reservoir (a/k/a Lake Powell) are a hard day’s drive from Central Colorado, but water levels there could have a major effect on life hereabouts.
The dam is on the Colorado River, which drains the Western Slope of Colorado. The facility in northeastern Arizona generates electricity (a sign there claims Buena Vista as one destination for the power), and it also stores water to help implement the Colorado River Compact, a 1922 agreement among the seven states touched by the Colorado River.
The compact is complex, but in essence, there are four Upper Basin states (Colorado, Wyoming, Utah, and New Mexico) and three Lower Basin states (California, Arizona, and Nevada). Under the Compact, the Upper Basin guarantees to deliver 7.5 million acre-feet a year to the Lower Basin, and the Upper Basin gets to use what’s left — Colorado is entitled to a little more than half of the Upper Basin share.
Powell Reservoir, with its millions of acre-feet of storage, helps insure that the Upper Basin can meet its obligations. If they suffer from a couple of dry years and river flows are low, they can just release stored water to the Lower Basin. Think of it as a savings account.
But what if there’s a long string of dry years, and the savings account faces depletion?
That scenario could be playing out now. Powell Reservoir now sits at only 42% of capacity, and this spring’s run-off isn’t expected to raise it enough to matter. The U.S. Bureau of Reclamation, which operates the reservoir, says it could drain completely if the current drought continues for another two or three years.
Colorado water law relies on seniority to determine who gets what when there isn’t enough water to go around. The Compact has a 1922 “appropriation date.” So users with a priority date before 1922 could still get their water; those with later priority dates would have to stop taking water if there were a “call” on the river on account of the Compact.
No more water could be stored in the three Aspinall Unit reservoirs west of Gunnison (Blue Mesa, Morrow Point, and Crystal), since they have 1957 priority dates, 33 years junior to the Compact.
Some Western Slope diversions into the Arkansas basin could continue. For instance, the Ewing Ditch across Tennessee Pass (now supplying Pueblo with about 1,000 acre-feet a year) has an 1880 priority date.
But it may be the only one that wouldn’t be affected by a Compact call on the Colorado. The big diversions came quite a while after 1922. The Boustead Tunnel, which supplies about 60,000 acre-feet a year of Western Slope water to the Fryingpan- Arkansas project, has a 1957 priority date. The Twin Lakes Tunnel supplies about 40,000 acre-feet a year to the Arkansas basin, and it’s got a 1935 priority date.
Other diversions into the Arkansas basin, like Homestake, the Busk-Ivanhoe Tunnel, and various ditches, all came after 1922. (The Busk-Ivanhoe Tunnel was bored in 1891-93 for the Colorado Midland Railroad, but didn’t begin moving water until the 1930s). And the big diversions into the South Platte basin (i.e., Colorado-Big Thompson, Moffat Tunnel, Roberts Tunnel) likewise came after 1922.
So if Powell continues to drop, Colorado could face some serious water-supply problems. Almost all of the water now diverted from the Western Slope would have to be allowed to flow to the Lower Basin. One bright spot: We wouldn’t have politicians talking about how Colorado has all this unused Western Slope water that should be developed.