Plummeting lake levels threaten Mesa’s water supply | News
Arizona and other Western states that take water from the lower Colorado River for cities and farms have been hoping for a good season of rain and snow this winter to keep water levels in the river’s reservoirs above dangerously low levels.
Instead, they got another bad year.
The dry year, on top of 22 years of regional drought, has shortened the time that states and the US Bureau of Reclamation have to avert a series of dangerous scenarios that could unfold in the next two years without action.
About 36% of Arizona’s water – and 55% of Mesa’s water – comes from the Colorado River. Lake Mead and Lake Powell store water that goes to population centers, and they have less water now than they’ve ever had.
The upshot of the disappointing winter is that water officials are accepting a future where less Colorado River water is available– so they are redoubling efforts to make alternate plans.
But at the same time that they are doing long-term planning, water officials are also engaged in a short-term rescue mission to keep the Colorado River flowing and the reservoir system intact.
A U.S. Bureau of Reclamation 24-month study predicts that without action, Lake Powell could drop below the level needed to generate hydropower, 3,490 feet, by next spring or as early as the end of December.
In briefings last week, officials noted that the reservoirs are V-shaped, which means the rate that the water levels drop accelerates at lower levels.
“We’re being piled on in a lot of ways, including by Mother Nature,” Arizona Department of Water Resources Director Tom Buschatzke said in a joint briefing with the Central Arizona Project last week.
While Buschatzke stressed that there is no “imminent threat” to water flowing from the tap in Arizona homes and businesses, officials made clear that Arizona and other states face a gauntlet of bad scenarios if they can’t halt the decline in Colorado reservoirs.
The most immediate threat to the Colorado water system is the loss of hydropower generated by the dams that hold back the water, when the level drops below the intake for the turbines.
Rural communities, like, rely on that hydropower, but it’s also “a crucial part of our (Arizona) energy grid,” Glendale Water Resources Manager Drew Swieczkowski said in a presentation last week. “It’s a really big energy producer.”
CAP, the state agency that delivers Colorado River water via canals and water credits, only relies on hydropower for 6% of its energy needs, but the loss of power would put upward pressure on water rates.
After losing power production, the next problem dam engineers would face is the need to release water from the reservoir via rarely used low water outlets. Dam operators don’t want to rely on these because they have little experience using them.
“There are reliability concerns about long-term operations and a lot of uncertainty,” Buschatzke said of dam operations at extremely low water. “I think you’ll hear that word ‘uncertainty’ quite a bit today in terms of what’s facing us.”
One-hundred and twenty feet below the loss of hydropower, Lake Powell would reach a “dead pool,” when water is below the low water outlet and there is no more active storage.
At the dead pool on Lake Powell, “the maximum amount that could be released (from the dam) is limited to the amount coming in, so-called“ run of the river, ”a spokesman for CAP said.
CAP said it could continue to deliver to cities through its canals as long as Lake Mead stayed above the dead pool. The agency also has secondary storage in Lake Pleasant north of Phoenix, for “critical deliveries to Phoenix-area cities.”
Many Valley cities, including Mesa, have diversified water portfolios, drawing water from groundwater and surface water other than the Colorado River. In a worst-case scenario, cities could keep the taps running for years using stored groundwater and water from the Salt River Project.
But a rapid reduction in cities’ allocations of Colorado River water would still likely have local officials scrambling to keep water operations steady. Many cities, including Mesa and Glendale, are drilling new wells to enhance their ability to quickly add groundwater to their water utilities.
One bit of good news is a large share of Mesa’s water comes from SRP, and SRP’s reservoirs on the Salt and Verde Rivers are currently healthy, Swieczkowski said, sitting at 77% and 33%, respectively. SRP is studying a plan to raise the height of Bartlett Dam, located 48 miles northeast of Phoenix, to improve storage capacity on the Verde River.
The bad year on top of many bad years seems to have forced water officials’ to face the reality that Colorado will permanently deliver less water each year, and it has galvanized officials to act.
Climate change is one reason water officials are resigned to reducing dependence on the Colorado River.
One of the findings from this year’s April water study was that much less water reached the river than actually fell as snow and rain in the watershed. In terms of snowpack, it actually wasn’t that bad a year, with 92% of the average.
But that snowfall only led to 62% of the average inflow to the reservoirs. Officials blame drier soil soaking up more water.
It is a “troubling trend that we do seem to be getting precipitation,” Bureau of Reclamation Deputy Chief Dan Bunk said. “But other factors such as warmer temperatures, dry soil conditions, increased evapotranspiration, they all seem to be conspiring to some extent against the actual runoff that is occurring on the system.”
Officials are talking frankly about reduced flows of the river.
Swieczkowski spoke of the “aridification of the Western US” to describe the long-term reduction in soil moisture due to climate change. He said the Colorado River now has a new estimated annual yield of 10 to 11 million acre-feet of water, compared to 16.5 MAF allocated to US states and Mexico.
This reckoning with Colorado’s oversubscription has energized long-term planning and water development efforts, and stimulated cooperation among local and federal officials.
“We can’t rely on Mother Nature somehow restoring the Colorado River to what’s been allocated,” one official said.
Officials in last week’s joint briefing appeared focused rather than discouraged.
Western states – including California, which has traditionally fought fiercely to hold onto its water – have been working together to keep extra water in the reservoirs. This year, states voluntarily left 500,000 acre feet of water in Lake Mead as part of the 500+ Plus compensated conservation program.
The city of Mesa contributed 1,200 acre feet of water to that effort.
Buschatzke said this and other conservation efforts have added 70 feet of elevation to the reservoirs, buying planners valuable time.
California, Arizona and Nevada are currently working on another version of 500+ Plus for 2023. Officials expect voluntary cuts like these, on-top of cuts already outlined in the drought contingency plans, to keep the Colorado River flowing.
“It won’t stop at 2023, but one year at a time,” Buschatzke said.