Originally Posted by
Zog
I don't know about knowing my stuff. My wife says I am full of BS!
Colorado River management is complicated by the Colorado River Compact, drafted in 1922. Water allocations were roughly split in half under the assumption that the river long-term average water supply was 15 MAF. The lower basin (Arizona, Nevada, California) were to be guaranteed 75 MAF over a 10 year period. The upper basin (Wyoming, Colorado, Utah, New Mexico) would be able to take the rest. The lower basins split their allocation in specific amounts, while the upper basin allocated percentages based on what was available. The thought was that the upper basin would be able to take more than the 7.5 MAF since the thought at the time was that there was more than 15 MAF in the system, but the upper basin was not guaranteed any water, just anything over 7.5 MAF. Later, Mexico was granted an allocation of 1.5 MAF through international treaty, so in essence the upper basin MUST deliver 9 MAF to the lower basin every year.
Hoover Dam (Lake Mead) was constructed to deliver the lower basin flows when the lower basin wants them. Glen Canyon Dam (Lake Powell) was constructed to allow the upper basin to take consistent water allocations year to year while also delivering the 9 MAF allocation every year. Lake Powell has continuously met the requirement for delivery to the lower basin until the last couple years, even with some extreme swings in water depth (Lake Powell is currently about 170 feet below full depth) while Lake Mead has also been overdrawn by lower basin users over the last 20 years, resulting in swings in Mead (currently about 180 feet below full depth).
With the drop in Lake Mead water levels, the allocation to Arizona goes down as a result of negotiations for federal funding for the Central Arizona Project. California and Nevada are guaranteed their allocations. Mexico also has a shortage allocation. Therefore, the volume required to be delivered by Powell goes down in order to prop up both lakes/dams. California and Nevada used to always take more than their allocation due to surplus water in the river system, but that has been reigned in now that there are shortages, so they are currently taking up to their allocation. Arizona has been hit with shortages the past 2 years. The upper basin states have not done much to reign in their diversions, which tend to be trans-basin diversions, with water going to Salt Lake City, Denver, and Colorado Springs, but we tend to argue that we are taking way less than the lower basin (4.5 MAF) so we are being robbed by the Compact. The Compact clearly needs to be renegotiated to deal with the hydrologic realities in the system in an extended drought condition.
Lake Powell and Lake Mead have been suffering for the past 20 years, though Mead has been much more stable. Lake Powell has fluctuated over 110 feet over the past 5 years, while Lake Mead has fluctuated about 50 feet. Two really good years would be able to restore Lake Powell to a reasonable level as the best rise over the past 5 years was over 50 feet in rise and currently lower surplus volumes have greater level impacts due to the lower volume currently in storage (like filling a martini glass). Once Lake Powell hits a level of 3605, USBR balances increasing the level of Mead with the level of Powell and plans some bumps in flow to help bring up the level of Mead, though balancing still occurs at lower levels.
As one in the water business, I can state that sandm is absolutely correct about the return to bad habits when there is good rainfall. Everyone wants to take the plenty but doesn't want to plan for the famine. I speak with lots of industrial users that start planning expensive reuse and water minimization projects during drought years, but they get cancelled when the shortage goes away. Agriculture is the MAJOR user in the basin though, with 85% of the water going there. There need to massive improvements in watering practices and perhaps some justification regarding where the water is going (Imperial Valley) before we run out of water in the system. California has been working to reduce demand but too slowly. Meanwhile, Colorado and Utah are trying to take more and more. This is all completely unsustainable.