Despite a below-average year in the Upper Colorado River Basin, Lake Powell will reach its summer peak this year at its highest level in four years. That comes despite the fact that, once again, the Upper Basin is releasing “bonus” water from Glen Canyon Dam to prop up water users in Arizona, Nevada, California, and Mexico. From Lake Powell Life:

“The silent but important statistic is that Lake Powell has provided extra water to Mead in five of the past 10 years, including the giant release of 12.5 maf in 2011….”

Lake Powell, courtesy USBR

The “bonus water” is part of the agreement under the 2007 “interim guidelines“, which include a Rube Goldberg contraption of a ruleset that governs how much water is released under varying reservoir conditions. The “normal” release is 8.23 million acre feet (I call it “normal” because I despair of finding words that all the lawyers can agree on). This year’s planned release is 9 million acre feet, based on the idea that balancing the contents of the two reservoirs is a good idea.

Powell’s at elevation 3,619 today. That’s nearly a hundred feet above the critical threshold of 3,525, below which Powell starts to have problems generating power and delivering needed water downstream. That sounds like a lot, but remember that Powell dropped near 100 feet in the first four years of the 21st century. As you can see from the graph, Powell’s been rising slowly, but it can drop in a hurry.