Folks worried that Lake Mead might drop below elevation 1,075 and trigger a first-ever Lower Colorado River Basin shortage now have more to worry about. The latest monthly model runs from the U.S. Bureau of Reclamation (pdf) have increased the odds, and suggest that Mead (currently at 1,077.03) could drop all the way to 1,054 by the end of the 2016 “water year” – 18 feet lower than projected just one month ago.
This is all a result of the interaction of two important water management rules – one that calls for holding more water upstream in Lake Powell to keep that reservoir from dropping too far, and a second that calls for curtailing water deliveries to Arizona, holding the water back in Lake Mead, outside Las Vegas.
The latest monthly Bureau model runs, released this afternoon, point toward a likely need to cut releases from Lake Powell, on the Colorado River along the Arizona-Utah border, beginning Oct. 1. That would result in less water being delivered to Lake Mead, downstream, increasing the chances of a first-ever shortage declaration and cascading shortfalls in Arizona as early as Jan. 1. So far odds are against that second eventuality – Arizona cuts beginning Jan. 1. But it’s very close right now, with projected Jan. 1 levels of 1,075.92, just 11 inches from the trigger point.
Regardless of whether we hit the 1,075 trigger this time around, however, reduced releases from Lake Powell would ensure huge drops in Lake Mead next year.
This is all part of the complicated operating rules adopted in 2007 intended to balance shortfalls in Powell, the main upper basin storage reservoir, and Mead, the main reservoir downstream for use by Nevada, Arizona, and California. Powell has been hovering right around a trigger point (elevation 3,575 feet above sea level on Jan. 1) that would require cutbacks to keep more water in Powell. There’s a lot of “if this then that” rules stumbling over one another here, but if the August monthly modeling run shows Powell is too low, that automatically invokes a rule to hold more water in Powell and release less water to Mead. And less water in Mead translates to increased risk of triggering a second rule that would keep more water in Mead next year by cutting deliveries to Arizona.