It was another bad year on the Colorado River, and the numbers prove it.
• River flows into Lake Powell at the Arizona-Utah border were 43 percent of normal in water year 2017-2018, which ended at the end of last month. That’s the lowest since the extreme drought year of 2002, when they were 24 percent of normal. It’s the third lowest annual flow into Powell since records on river flows started being kept in 1906.
• The river’s annual flows were above average in only four of the 19 years since 2000. This was the river’s driest 19-year period on record.
• The combined storage of river water in Lake Powell and Lake Mead is about 41 percent of normal. It’s the lowest combined storage since Lake Powell was filling during the mid-1960s after the closing of the gates at the newly constructed Glen Canyon Dam.
• This year’s flows into Lake Powell were far less than the federal forecast back in April of about 52 percent of normal. One reason is that flows into Powell were 1 percent of normal in September — the driest on record — and 2 percent of normal in August — the second driest on record.
“We had a pretty good year in 2017, with an inflow into Powell of 110 percent of average. But unfortunately we lost that storage and a little bit more in 2018,” said Dan Bunk, a U.S. Bureau of Reclamation hydrologist.
He presented these and other figures Wednesday at a meeting of the steering committee working on a proposed Drought Contingency Plan for the river’s Lower Basin.
“Really that buffer that we saw in Lake Powell, the extra storage that helped protect the Colorado River system, was lost this year,” Bunk said.
The bureau predicts a 57 percent chance of the river’s first shortage in 2020, with the odds of shortages increasing in future years. That would happen if Lake Mead drops below 1,075 feet at the end of 2019.
Without a formal Drought Contingency Plan in place, under which less water would be used, there’s about a 75 percent chance of Mead dropping below 1,050 feet by 2026, which would require deeper cuts in deliveries, the bureau says.
That’s based on assuming the trends of declining river flows from 1988 to 2015 continues. With a drought plan, the odds of Mead dropping below 1,050 by then fall to a little over 50 percent.
Without a drought plan, there’s also at least a 40 percent chance of Mead dropping below 1,025 feet from 2024 through 2026, bureau figures show, based on the same 1988-2015 flow record. With a plan, the odds of such low levels drops to less than 20 percent for all those years and to as low as 10 percent in 2024.
At 1,025 feet, a federal takeover of how the river’s flows are divided is possible, as federal officials would want to keep the lake from sinking lower and approaching “dead pool” at 895 feet, when no water could be pulled from Mead.