Tag Archives: Bureau of Reclamation

Drought, Water, Water supply

Plotting “dead pool” and other watersheds for Lake Powell and Lake Mead

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The elevations of Lake Powell and Lake Mead, two critical reservoirs on the Colorado River, are like the Dow and S&P 500 for water in the Southwest. These closely watched metrics serve as simple barometers and summaries of how things are going in a fiendishly complex system, be it the U.S. economy or a watershed spread across a quarter-million square miles that provides drinking water for nearly 40 million people.

“Water buffaloes,” the professionals who manage the West’s most precious resource, have been sounding bearish in recent days about Powell and Mead, the nation’s two largest reservoirs by capacity. The past 14 years have been the driest for the Colorado River in more than a century of record keeping. On Friday, federal officials announced they will cut releases from Powell from 8.23 million acre-feet to 7.48 million acre-feet, which would be lowest release since the reservoir was filling in the 1960s.

To track water storage in Powell and Mead, I’ve created a dashboard that plots the lake levels and some important benchmarks. Below are some images from the visualization (click to enlarge). There’s also a PowerPoint presentation you can download at the bottom of the post.

Lake Powell elevation graphic Lake Mead elevation graphic

Elevation benchmarks

The Powell chart plots the daily elevation and the Mead chart illustrates the July 1 level; in the former, you can see the annual ebb and flow. I used two different time scales because that’s how I found the data on the U.S. Bureau of Reclamation’s websites (separate offices manage Powell and Mead).

Capacity shows the elevation when the reservoirs are full. For Powell, raising the spillway gates can slightly increase capacity, but flooding in 1983 did nearly overtop Glen Canyon Dam. When a reservoir is at dead pool, the water level is so low that it cannot drain by gravity through the dam’s outlet works. Hydropower can only be generated when the reservoir is above the minimum power pool. For Mead, which supplies the Las Vegas metro area, the elevation of the Southern Nevada Water Authority’s lower intake is shown.

Our dashboard uses lake elevation, but in our PowerPoint deck we also have some slides showing changes in volume. Each metric tells us different things about the status of the reservoirs, but elevation is easier to visualize. Below is a photo I took last April of Powell’s so-called bathtub ring, which is even more exposed today.

Lake Powell and Glen Canyon Dam
Lake Powell and Glen Canyon Dam, April 2012. Photo by Mitch Tobin.

Satellite imagery shows Powell’s decline

Another way to track the status of these reservoirs is by taking repeat photographs, either on Earth or from space, of the same location. Below are two views of Lake Powell, the first showing 2002 vs. 2003, and the second comparing 2012 vs. 2013, based on NASA satellite imagery.

Lake Powell drought photograph

Lake Powell satellite image drought

The PowerPoint deck that you can download below contains a time series of satellite images of Powell from 1999 to 2013. The contrast between 2012 and 2013 illustrates why federal officials are taking action and cutting releases from the reservoir.

Reservoir levels projected to fall

Looking ahead, federal water managers project that Mead will drop another eight feet in 2014 due to reduced releases from Powell. Below is a graphic from Reclamation that shows Powell is likely to keep falling as well.

Lake Powell elevation projection

Basin susceptible to megadroughts

The outlook for precipitation in the basin over the next few years is uncertain, but one thing we know for sure is that the Colorado River is vulnerable to megadroughts, the likes of which we haven’t seen in modern times. The graphic below, from the U.S. Climate Change Science Program, shows the annual flow of the Colorado River over the past 1,200 years. Scientists used tree rings to estimate the river’s volume before the instrumental record, which is shown as a red line. The arrows point out that the basin has been periodically hit with megadroughts that were worse than the one we’ve been experiencing since 2000.
Colorado River drought tree ring record

Climate change expected to shrink Colorado’s flow

Even without considering climate change, the Colorado River would face a challenging future because the demand for its limited–and capricious–supply is increasing along with the Southwest’s population. But scientists project that even less water will flow down the river in the decades to come due to rising temperatures and altered precipitation patterns. The graphic below, from Reclamation’s recent Basin Study, shows that demand is projected to exceed supply on the river (see our earlier post for more details).

Colorado River historical and projected water use and supply

Data sources

The Bureau of Reclamation provides detailed data on Lake Powell and Lake Mead. I pulled the benchmark levels from this Reclamation presentation, specifically page 15.

If you’re keeping score at home, the capacity of elevation of Powell is listed as 3,700 feet, but during floods the reservoir’s elevation can go slightly above this level by raising the spillway gates. In 1983, Powell reached an all-time high elevation of 3,708.34 feet.

The decision to cut releases from Powell was covered by The Arizona Republic,  National Public Radio, and The Salt Lake Tribune, among others.

Downloads

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Conservation, Water, Water supply

Visualizing Colorado River challenges and options

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The Colorado River, lifeblood of the Southwest, is in trouble. Demand for river water is rising as the region’s population continues to grow, but the Colorado’s inherently capricious supply is increasingly in doubt due to climate change.

A federal report released in December took an exhaustive look at the challenges facing the Colorado River Basin and it examined the options for dealing with expected shortages.  I’ve gone through the Colorado River Basin Water Supply and Demand Study and pulled out the key figures, which you can download at the bottom of this post.

Colorado River Bain Study from EcoWest on Vimeo.

Shortage projected

If I had to pick one graphic that summed up the dilemma facing the Colorado River, it would be this one:

Colorado River historical and projected water use and supply

Looking back in time, the graphic shows that water use in the basin steadily increased during the 20th century, but the river’s flow was predictably erratic (that blue line is a 10-year moving average but it’s still as uneven as the basin’s topography).

Looking ahead, water demand is expected to keep growing (the fuzzy areas indicate the uncertainty in the projections). Predicting the flow of the Colorado decades into the future is a tough task, but the study concluded that the supply would probably decrease, as indicated by the gentle downward slope of the blue line. By 2060, the imbalance between supply and demand is expected to be about 3.2 million acre-feet.

Comparing costs of solutions

Besides identifying the problem, the Basin Study evaluated a wide variety of proposals for addressing the shortfall—everything from increasing water conservation in cities and on farms, to building massive new pipelines and desalination plants, even far-fetched ideas like towing icebergs to Southern California.

I extracted data from a summary table in the study in order to visualize how these options compare, both in price and in how much water they’ll yield.

In the graphic below, I’ve ranked all of the options from highest to lowest cost (the unit here is dollars per acre-foot per year). I’ve also color-coded them by category.

Cost of options for Colorado River

As you can see, the range of costs is enormous, but there are some general patterns. Conservation measures are among the cheapest, while desalinating ocean water or covering reservoirs to reduce evaporation are pricey. (For a few of these options, the study provided a range of costs, but for simplicity’s sake I’ve used the average in this graphic.)

The chart below ranks the options by how much water they’re expected to yield in 2035.

Potential yield of options for Colorado River

Water conservation in agriculture and among municipal and industrial (M&I) users is projected to yield the most, but weather modification (aka cloud-seeding) also performs well on this measure.

I combined the cost and yield data into one graphic by varying the width of the bars by the volume of water that each strategy is expected to produce. The thicker the bar, the greater the yield. In this case, I used the projections for 2060, rather than 2035.

Cost and yield of options for Colorado River

In releasing the Basin Study in December, federal officials stressed the conservation options over massive new infrastructure projects, such as pumping the Missouri or Mississippi rivers to the Colorado Front Range. These graphics show why that’s pretty much a no-brainer: conservation delivers more bang for the buck and avoids the enormous environmental impacts of augmentation projects.

Downloads

Data sources

You can download the Basin Study and associated reports here.

The Denver Post had a good overview of the Basin Study’s release. See recent stories by the Los Angeles Times and Associated Press  for more on what the federal government is doing to follow up on the report.

EcoWest’s mission is to analyze, visualize, and share data on environmental trends in the North American West. Please subscribe to our RSS feed, opt-in for email updates, follow us on Twitter, or like us on Facebook.