With the 2009 “water year” just completed, it’s time to take stock. The decade just completed, 2000-2009, is the driest 10-year period in the Colorado River Basin in the record, according to preliminary data in the latest draft of the Bureau of Reclamation’s Colorado River Annual Operating Plan, a compendium of past data on the river and plans for the coming year:
Provisional calculations of natural flow for the Colorado River at Lees Ferry, Arizona, show that the average natural flow since calendar year 2000 (2000-2009, inclusive) is 11.933 maf (14,719 mcm), the lowest ten-year average in over 100 years of record keeping on the Colorado River.
Recall that the Colorado River Compact assumes 16.5 million acre feet (maf) average flow on the river, divided 7.5 maf for the upper basin states, 7.5 maf for the lower basin states, plus 1.5 maf for Mexico. For the last decade, the river has averaged just 72.3 percent of that amount.