Tracking the water supply in Lake Mead and Lake Powell

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Graphics and slides showing changes in Lake Mead and Lake Powell, two reservoirs on the Colorado River.

Graphics and slides showing changes in Lake Mead and Lake Powell, two reservoirs on the Colorado River.

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  • This presentation examines some metrics for tracking the water supply in Lake Mead and Lake Powell.
  • Narrative: One way of looking at reservoir storage is the lake’s elevation above sea level. Imagine a giant ruler printed on the upstream face of the dam or one of the cliff walls. Here’s Lake Mead’s elevation, along with some critical levels. Green shows full storage at 1,229 feet. The minimum for generating hydropower is 1,050 feet. The intake for the Southern Nevada Water Authority, which supplies Las Vegas, is at 1,000 feet, and what’s known as dead pool, when the reservoir is so low that no more water will drain from the dam’s outlet works, is at 895 feet. Source: US Bureau of ReclamationURL: http://www.usbr.gov/lc/riverops.html http://www.usbr.gov/lc/region/programs/strategies/presentations/Nov2005.pdfNotes:
  • Narrative: Here’s Lake Powell’s elevation, along with some critical levels. In green is full storage, 3,700 feet. You can see that the 1983 flood was actually above that level, 3,708 to be exact, because the Bureau of Reclamation is able to raise the spillway gates a little bit. The minimum for generating hydropower is 3,490 feet, and dead pool is 3,370 feet.Source: US Bureau of ReclamationURL: http://www.usbr.gov/uc/crsp/GetSiteInfo http://www.usbr.gov/lc/region/programs/strategies/presentations/Nov2005.pdfNotes:Elevation 3,700 feet msl corresponds to the top of the spillway radial gates. During floods, the elevation of Lake Powell can go above 3,700 feet msl by raising the radial spillway gates, resulting in spillway releases. In 1983, Lake Powell reached a high elevation of 3,708.34 feet msl.
  • Narrative: This graphic shows that Lake Powell’s elevation is expected to fall over the next couple of years.Source: US Bureau of ReclamationURL: http://www.usbr.gov/uc/crsp/GetSiteInfo
  • Narrative: Let’s take a closer look at Hoover Dam and Lake Mead. This graphic shows how the flows of the Colorado River—what’s known as a hydrograph—changed when Hoover Dam was completed in 1935. Prior to the dam, the Colorado River’s flow varied dramatically and sometimes exceeded 100,000 cfs, but since the 1930s, the volume of the flow and the variability has been reduced dramatically. The one event that really sticks out is the extremely wet period around 1983.Source: US Bureau of ReclamationURL: http://www.usbr.gov/lc/riverops.htmlNotes:
  • Narrative: Here’s a graphic showing the volume of both reservoirs. You can see that Lake Mead, in green, started to fill in 1935, and that Lake Powell, in blue, began to fill in 1963.Both lakes were nearly full during the 1983 floods and for much of the 1980s. The early 1990s were dry, but by 1999 the two reservoirs were full again. Then both went into free fall after the severe drought in the early 2000s. Source: US Climate Change Science Program/Bureau of ReclamationURL: http://downloads.climatescience.gov/usimpacts/pdfs/climate-impacts-report.pdfNotes:
  • Narrative: Drought is an inherent part of the climate in the West. We know from tree ring studies and other research that the region will occasionally enter a long-term droughts, the likes of which we haven’t seen in modern times. In this graphic, the black line shows the percentage of the West affected by drought (Palmer Drought Severity Index less than –1) over the past 1,200 years. The red horizontal line indicates the average drought area in the years 900 to 1300. The blue horizontal line in the yellow box indicates the average during the 20th century. This more recent period, during which population and water infrastructure grew rapidly in the West, was much wetter than the long-term average, which is indicated by the thin horizontal black line. Source: US Climate Change Science ProgramURL:http://downloads.climatescience.gov/usimpacts/pdfs/climate-impacts-report.pdf
  • Narrative: The Colorado River’s history has been reconstructed back over 1200 years, based primarily on tree-ring data. These data reveal that some droughts in the past have been more severeand longer lasting than any experienced in the last 100 years. The red line indicates actual measurements of river flow during the last 100 years. The arrows point to what some call “megadroughts.” Climate models suggest that droughts will become more severe over time, partially due to a northward shift in winter and spring storm tracks.Source: US Climate Change Science Program, Meko et al. URL: http://downloads.climatescience.gov/usimpacts/pdfs/climate-impacts-report.pdf
  • Narrative: These matching photographs were taken 18 months apart during the 2002-2003 drought.Source: US Climate Change Science Program, Photos by John DohrenwendURL: http://downloads.climatescience.gov/usimpacts/pdfs/climate-impacts-report.pdfNotes:
  • Narrative: Source: US Climate Change Science Program, Photos by John DohrenwendURL: http://downloads.climatescience.gov/usimpacts/pdfs/climate-impacts-report.pdfNotes:
  • Narrative: Source: US Climate Change Science Program, Photos by John DohrenwendURL: http://downloads.climatescience.gov/usimpacts/pdfs/climate-impacts-report.pdfNotes:
  • Narrative: Here’s a sequence of satellite photos of Lake Powell in Southern Utah. Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:The Colorado River flows from the Rocky Mountains in Colorado through the southwestern United States. Along its route, the river passes through an elaborate water-management system designed to tame the yearly floods from spring snowmelt and to provide a reliable supply of water for residents as far away as California. The system is appreciated for the water it supplies, but criticized for the environmental problems and cultural losses that have resulted from its creation. Among the dams on the Colorado is Arizona’s Glen Canyon Dam, which creates Lake Powell. The deep, narrow, meandering reservoir extends upstream into southern Utah. In the early twenty-first century, this modern marvel of engineering faced an ancient enemy: severe, prolonged drought in the American Southwest. Combined with water withdrawals that many believe are not sustainable, the drought caused a dramatic drop in Lake Powell’s water level over the past decade. The changes are documented in this series of natural-color images from the Landsat 5 satellite between 1999 and 2011.The images show the northeastern reaches of Lake Powell. The Colorado River flows in from the east around Mille Crag Bend and is swallowed by the lake. At the west end of Narrow Canyon, the Dirty Devil River joins the lake from the north. (At normal water levels, the both rivers are essentially part of the reservoir). Sunlight brightens plateaus and southeast-facing slopes, casting shadows on the northern and western faces of the rugged landscape. At the beginning of the series, in 1999, water levels in Lake Powell were relatively high, and the water was a clear, dark blue. The sediment-filled Colorado River appeared green-brown. Throughout the first years of the next decade, water levels began to drop. The declines were first apparent in the side canyons feeding the reservoir, which thinned and then shortened. By 2002, the lake level had dropped far enough that the exposed canyon walls created a pale outline around the lake. Dry conditions and falling water levels were unmistakable in the image from April 13, 2003. Lake Powell’s side branches had all retreated compared to the previous year’s extents. Water levels in Narrow Canyon had dropped enough to show canyon floor features not visible in earlier images. In the image acquired on May 1, 2004, the reservoir’s northwestern branch is isolated from the main reservoir; the shallow water upstream could not crest raised areas in the lake bed. Lake Powell’s water levels plummeted in early 2005, according to the U.S. Department of the Interior Bureau of Reclamation, and the lowest water levels seen in this time series appear in the image from April 2, 2005. The northwestern side branch of Lake Powell remained cut off from the rest of the reservoir. In the main body of Lake Powell, water pooled along its eastern edge, while large expanses of dry canyon floor were visible in the west. In the latter half of the decade, the drought eased somewhat. Precipitation was near, but still slightly below average in the Upper Colorado River Basin. The lake level began to rebound; only the 2008 image appeared to deviate from the trend toward rising water levels. While the lake was significantly higher in May 2011 than in 2005, a careful comparison of the side canyons reveals that the level was still not back to 1999 levels, when the lake was near full capacity. The peak inflow to Lake Powell occurs in mid- to late spring as the winter snow in the Rocky Mountains melts. According to the U.S. Bureau of Reclamation, the April 2011 inflow to Lake Powell was 100 percent of the 30-year average, and significantly higher than most of the past decade. Extensive, heavy snowpack in the Rockies led hydrologists to predict a significant burst of fresh water into the lake in 2011, with a projected April through July flow at 145 percent of the average. The forecast for maximum elevation at summer pool, which usually occurs in late July or early August, was 3,656 feet above sea level, about 44 feet below full pool. A century of river flow records combined with an additional four to five centuries of tree-ring data show that the drought of the late 1990s and early 2000s was not unusual; longer and more severe droughts are a regular part of the climate variability in that part of the continent. Global warming is expected to make droughts more severe in the future. Even in “low emission” climate scenarios (forecasts that are based on the assumption that future carbon dioxide emissions will increase relatively slowly), models predict precipitation may decline by 20-25 percent over most of California, southern Nevada, and Arizona by the end of this century. Precipitation declines combined with booming urban populations will present a significant challenge to Western water managers in the near future.
  • Narrative: Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: By 2002, the lake level had dropped far enough that the exposed canyon walls created a pale outline around the lake. Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Dry conditions and falling water levels were unmistakable in the image from April 13, 2003. Lake Powell’s side branches had all retreated compared to the previous year’s extents. Water levels in Narrow Canyon had dropped enough to show canyon floor features not visible in earlier images.Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: In the image acquired on May 1, 2004, the reservoir’s northwestern branch is isolated from the main reservoir; the shallow water upstream could not crest raised areas in the lake bed. Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Lake Powell’s water levels plummeted in early 2005, according to the U.S. Department of the Interior Bureau of Reclamation, and the lowest water levels seen in this time series appear in the image from April 2, 2005. The northwestern side branch of Lake Powell remained cut off from the rest of the reservoir. In the main body of Lake Powell, water pooled along its eastern edge, while large expanses of dry canyon floor were visible in the west. Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: In the latter half of the decade, the drought eased somewhat. Precipitation was near, but still slightly below average in the Upper Colorado River Basin. The lake level began to rebound;Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Only the 2008 image appeared to deviate from the trend toward rising water levelsSource: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: While the lake was significantly higher in May 2011 than in 2005, a careful comparison of the side canyons reveals that the level was still not back to 1999 levels, when the lake was near full capacity. The peak inflow to Lake Powell occurs in mid- to late spring as the winter snow in the Rocky Mountains melts. According to the U.S. Bureau of Reclamation, the April 2011 inflow to Lake Powell was 100 percent of the 30-year average, and significantly higher than most of the past decade. Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: The peak inflow to Lake Powell occurs in mid- to late spring as the winter snow in the Rocky Mountains melts. Significant amounts of snowfall over the winter of 2010–2011 meant more water for Lake Powell, and this effect lasted into the spring of 2012, when inflow levels were even higher than they had been the previous spring. Regional snowfall in the spring of 2012, on the other hand, was abnormally low, and inflow to Lake Powell did not begin to increase in May 2012 as it had in the previous four years.Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Leading up to the spring of 2013, daily water levels between October 2012 and May 2013 were consistently five or more feet below the previous four years. The Bureau of Reclamation forecasted that inflow for April to July 2013 would be just 38 percent of average. By the end of the year, reservoir storage would be 42 percent of capacity.Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:
  • Narrative: Here’s a comparison of 2012 and 2013.Source: NASAURL: http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.phpNotes:

Transcript

  • 1. Tracking the water supply in Lake Mead and Lake Powell 8/21/2013
  • 2. Lake Mead July 1 elevation: 1935-2013 2Source: Bureau of Reclamation
  • 3. Lake Powell daily elevation: 1964-2013 3Source: Bureau of Reclamation
  • 4. Lake Powell: historic and projected elevations 4Source: Bureau of Reclamation
  • 5. 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 FLOW(1000CFS) Feb. 1935 Storage begins at Lake Mead July 1941 Lake Mead fills Mar 1963 Storage begins at Lake Powell June 1980 Lake Powell fills Dams dramatically alter natural hydrograph 5 Flow below Hoover Dam: 1906 - 2007 1983 floods Source: Bureau of Reclamation
  • 6. Lake Powell and Lake Mead storage 6Source: U.S. Climate Change Science Program/Bureau of Reclamation
  • 7. 7 1,200 years of drought in the West Source: U.S. Climate Change Science Program
  • 8. Recent droughts less severe for Colorado River 8 History of Colorado River Flow Source: U.S. Climate Change Science Program
  • 9. Lake Powell 9 Source: U.S. Climate Change Science Program/ Photos by John Dohrenwend
  • 10. Lake Powell 10 Source: U.S. Climate Change Science Program/ Photos by John Dohrenwend
  • 11. Lake Powell 11 Source: U.S. Climate Change Science Program/ Photos by John Dohrenwend
  • 12. 1999 1999 NASA 12Source: NASA
  • 13. 2000 2000 NASA 13Source: NASA
  • 14. 2001 2001 NASA 14Source: NASA
  • 15. 2002 2002 NASA 15Source: NASA
  • 16. 2003 2003 NASA 16Source: NASA
  • 17. 2004 2004 NASA Hite Marina 17Source: NASA
  • 18. 2005 2005 NASA 18Source: NASA
  • 19. 2006 2006 NASA 19Source: NASA
  • 20. 2007 2007 NASA 20Source: NASA
  • 21. 2008 2008 NASA 21Source: NASA
  • 22. 2009 2009 NASA 22Source: NASA
  • 23. 2010 2010 NASA 23Source: NASA
  • 24. 24 2011 Source: NASA
  • 25. 25 2012 Source: NASA
  • 26. 26 2013 Source: NASA
  • 27. 27 2012 2013 Source: NASA Lake Powell and the recent drought
  • 28. ecowest.org Download more slides and other resources 28