High flow experiment planned for early November to restore aquatic and riparian Colorado River ecosystems downstream of Glen Canyon Dam
By Summit Voice
FRISCO — Even with some bonus inflow in September, the past water year Oct 1, 2012 – Sept. 30, 2013) ended up as the fourth-driest on record for the Colorado River Basin as measured at Lake Powell — the key reservoir on the river that helps balance supply and demand between the upper and lower basins.
Overall water storage in the Colorado River Basin in the last 14 years has ranged from a high of 94 percent of capacity in 2000 to the present low of 50 percent at the start of the 2014 water year.
In a recent update, the U.S. Bureau of Reclamation reported that total inflow for the water year was just 5.12 million acre-feet, just 47 percent of average. Water years 2002, 1977, and 2012 were drier, receiving 2.64 maf, 3.53 maf, and 4.91 maf, respectively.
Lake Powell has only seen above-average inflows in three of the past 14 years. According to BuRec, the span between 2000 and 2014 is the driest 14-year period on record since the reservoir started filling in 1963, with an average annual inflow of about 8.25 million acre feet, or about 76 percent of the 30-year average between 1981 and 2010.
During the 14-year period 2000 to 2013, however, the unregulated inflow to Lake Powell, which is a good measure of hydrologic conditions in the Colorado River Basin, was above average in only 3 out of the past 14 years. The period 2000-2014 is the lowest 14-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.25 maf, or 76% of the 30-year average (1981-2010).
But monsoon moisture definitely gave the reservoir a boost, raising the water level by 2 feet during an 11-day stretch in September. For the month, the inflow was 857,000 acre-feet, about 210 percent of average. At the end of September, Lake Powell’s water level was more than 108 feet below full, at 45 percent of capacity.
When global warming is factored into the big-picture water equation, some studies have suggested Lake Powell may continue dropping for years to come. Research published by the U.S. Forest Service Rocky Mountain Research Station this year found that “Lakes Powell and Mead are projected to drop to zero and only occasionally thereafter add rather small amounts of storage before emptying again.”
Last summer, the Bureau of Reclamation announced it will probably have to cut deliveries to the Lower Basin states in the next couple years. This year, Lake Powell’s water level peaked June 18 at a level 35 feet lower than 2012. Storage in the reservoir dropped by 3 million acre feet from the previous year.
BuRec released about 8.2 million acre feet from the reservoir. Under a cooperative program, the agency plans a high flow experimental release Nov. 11 to Nov. 16, ramping up flows from Lake Powell as high as 37,200 cubic feet per second, lasting for four days to try and mimic beneficial high natural flows downstream of the reservoir.
The releases will drop the reservoir level by about 2.5 feet but won’t change the overall annual of water to be delivered downstream. More information is online at the BuRec Lake Powell website.
Related Information and graphics (courtesy BuRec):
* Glen Canyon Dam November 2013 HFE Release Hydrograph
* 2013 HFE Downstream Flow Arrival Time Map
* Lake Powell 2013 HFE Projected Elevation Graphs
* Lake Mead Projected Elevation Graphs