Lake Powell is the second largest constructed water reservoir by storage capacity in the United States and represents a critical component in management of water resources in the Colorado River Basin. The reservoir provides hydroelectric power generation at Glen Canyon Dam, banks water storage for the Upper Colorado River Basin, stabilizes water commitments downstream, and buffers the Lower Colorado River Basin, including Lake Mead, against sedimentation and fluctuations in hydrological conditions. With completion of the dam in 1963, Lake Powell steadily filled with water before reaching full pool in 1980 and has become a popular destination for recreation, welcoming more than 4 million visitors per year. Since the early 2000s, severe drought and increases in water demand have resulted in a significant drop in reservoir elevation and stored water, prompting a heightened level of interest in the current state and future of Lake Powell.
Beginning in 2017, the U.S. Geological Survey, in cooperation with the Bureau of Reclamation, completed topobathymetric surveys of Lake Powell for the first update of elevation-area-capacity relationships since 1986. This report presents results of these surveys and comparisons with estimates from previous surveys. The storage volume and surface area, as of completion of the topobathymetric survey in spring 2018, are calculated at 0.33-foot (0.10-meter) increments for elevations ranging from 3,120.08 to 3,717.19 feet above the North American Vertical Datum of 1988 (NAVD 88). Between 0.33-foot increments, the storage volumes and areas were linearly interpolated at 0.01-foot intervals. Interpolation error in the 0.01-foot interval estimates was assessed at lower (3,160.00–3,161.00 feet above NAVD 88), middle (3,400.00–3,401.00 feet above NAVD 88), and upper (3,700.00–3,711.00 feet above NAVD 88) elevations. The interpolated storage capacity and area estimates are comparable to the measured values with differences ranging from 0.00 to 0.02 percent and from −0.01 to 0.03 percent, respectively.
Current storage capacity at full pool (3702.91 feet above NAVD 88) is 25,160,000 acre-feet. Compared to previously published estimates, this volume represents a 6.79 percent or 1,833,000-acre-foot decrease in storage capacity from 1963 to 2018 and a 4.00 percent or 1,049,000-acre-foot decrease from 1986 to 2018. Areal extent, as of spring 2018, at full pool is 159,200 acres, which represents a 1.33-percent decrease from 1963 to 2018 and a 0.96 percent decrease from 1986 to 2018.
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Cover: (Front) Lake Powell, March 25, 2020. Photograph taken by Casey Root. (Back) Glen Canyon Dam, December 2, 2018. Photograph taken by Casey Root.
Funding for the data acquisition and work detailed in this report was provided by the Bureau of Reclamation.
Bathymetric data collection and processing was completed by Robert Baskin from the U.S. Geological Survey Utah Water Science Center and Brian Andrews, Wayne Baldwin, Charles Worley, Jane Denny, David Foster, Barry Irwin, Eric Moore, and Alexander Nichols from the U.S. Geological Survey Woods Hole Coastal and Marine Science Center. Integration of the lidar and bathymetric data was performed at the U.S. Geological Survey Earth Resources Observation and Science Center by Sandra Poppenga, Jeff Danielson, and Dean Tyler. Jed Parker, Nate Clifton, and Beau Uriona of the Bureau of Reclamation provided scientific support and managed lidar data acquisition.
The authors would also like to thank the scientists not specifically mentioned here for their efforts and contributions to this project, the organizations and cooperators that worked with the U.S. Geological Survey, the reviewers for their insight and expertise, and the editorial staff for their ability to effectively communicate this report to the public.
Multiply | By | To obtain |
Length | ||
---|---|---|
inch (in.) | 2.54 | centimeter (cm) |
inch (in.) | 25.4 | millimeter (mm) |
foot (ft) | 0.3048 | meter (m) |
mile (mi) | 1.609 | kilometer (km) |
Area | ||
acre | 4,047 | square meter (m2) |
acre | 0.004047 | square kilometer (km2) |
square mile (mi2) | 2.590 | square kilometer (km2) |
Volume | ||
acre-foot (acre-ft) | 1,233x10−6 | cubic kilometer (km3) |
Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:
°C = (°F − 32) / 1.8.
Vertical coordinate information is referenced to the North American Vertical Datum of 1988.
Horizontal coordinate information is referenced to the North American Datum of 1983 with the National Adjustment of 2011. Historical data were transformed from the North American Datum of 1927.
Data used in this report are in the Universal Transverse Mercator Zone 12 projection.
All elevations are referenced to the North American Vertical Datum of 1988 unless otherwise noted. The conversion factor from the National Geodetic Vertical Datum of 1929 to North American Vertical Datum of 1988 in this study area is 2.913 feet, as determined using the VERTCON tool produced by the National Oceanic and Atmospheric Administration (
Elevation-area-capacity relationships presented here are not directly comparable to those used in Bureau of Reclamation operations at Glen Canyon Dam.
Computer Aided Resource Information System Hydrographic Information Processing System
digital elevation model
U.S. Geological Survey Earth Resources Observation and Science Center
National Oceanic and Atmospheric Administration
Bureau of Reclamation
root mean square error in the vertical direction
U.S. Geological Survey Station Identifier
topobathymetric digital elevation model
U.S. customary system
U.S. Geological Survey
The U.S. Geological Survey (USGS), in cooperation with the Bureau of Reclamation (Reclamation), surveyed Lake Powell between fall 2017 and spring 2018 to produce an integrated topobathymetric dataset, which comprises topographic light detection and ranging (lidar) data (land elevation) and multibeam bathymetry (bed elevation of a water body), for the purposes of calculating the elevation-area-capacity relationships in Lake Powell. Lake Powell is located on the Colorado River across the Utah–Arizona border (
Location of Lake Powell and the Glen Canyon National Recreation Area, Utah and Arizona. Stream lines and watershed boundaries from U.S. Geological Survey NHDPlus High Resolution dataset (
1. Map showing location of Lake Powell and the Glen Canyon National Recreation Area, Utah and Arizona
Though the instrumental record of the Upper Colorado River Basin is robust, with daily streamgage monitoring dating to the 20th century (
Bathymetric and topographic lidar surveys were done in 2017 (
Lake Powell is located on the border of Utah and Arizona, with maximum extents that flood nearly 200 miles upstream on the Colorado River. The lands surrounding the reservoir, the Glen Canyon National Recreation Area, are under the stewardship of the National Park Service and Reclamation (
Reservoir elevation and measured inflow by calendar year since 1961.
2. Graphs showing reservoir elevation and measured inflow by calendar year since 1961
The reservoir elevation for Lake Powell has been reported daily since December 28, 1963, by Reclamation, in addition to other parameters such as storage, inflow, and outflow. Reservoir elevation is recorded hourly, relative to the National Geodetic Vertical Datum of 1929 (NGVD 29), in a stilling well within Glen Canyon Dam, and the last value of each day, at 11:00 p.m. (Mountain Standard Time), is reported (Bureau of
The main tributaries of Lake Powell are the Colorado and San Juan Rivers, with substantially lesser contribution from the Escalante and Dirty Devil Rivers (
The current areal extent of the reservoir at full pool is approximately 250 square miles (mi2), reaching Cataract Canyon on the Colorado River and Clay Hills Crossing on the San Juan River (
The distinctive red rocks of the Colorado Plateau characterize the regional bedrock and range in age from Late Pennsylvanian to Late Cretaceous periods (318–66 million years ago). Cliff-forming units, primarily the Navajo Sandstone and Wingate Sandstone of the aptly named Glen Canyon Group, construct the deep and narrow canyons of Lake Powell. Incision of the Colorado River into the bedrock over the last 5 million years formed Glen Canyon (
Reclamation published two surveys with estimates of elevation-area-capacity relationships of Lake Powell: (1) the original, pre-Glen Canyon Dam storage estimates (Bureau of
Detailed contour maps of Glen Canyon were commissioned during the planning stages of Lake Powell to estimate storage capacity (
A bathymetric survey completed by Reclamation (
Several studies have been done on sedimentation and storage loss in Lake Powell, though they do not include reservoir-wide estimates for storage capacity. To monitor sedimentation, Reclamation performed a series of sediment monitoring range-line surveys of the deltaic regions of the Colorado and San Juan Rivers between 1968 and 1973 (Bureau of
A TBDEM is a continuous representation of subaerial topography and submerged bathymetry.
Select locations in Lake Powell that display data sources for the original (
3. Maps showing select locations in Lake Powell that display data sources for the original and modified topobathymetric digital elevation models
A dual-head Reson T20-P multibeam echosounder was used to collect reservoir-wide high-resolution bathymetry between October 8 and November 15, 2017 (
The lidar topographic data were acquired during a 2-day airborne survey on April 2 and April 3, 2018, and completed by The Atlantic Group, LLC (https://www.atlantic.tech), under contract by Reclamation. This dataset is not independently published as of the release of this report. A Pacific Aerospace PAC750XL (N750VX) outfitted with a Leica ALS70-HP topographic lidar system was used for data collection, with a maximum flying height of 11,500 ft above ground level. The vertical accuracy of the point cloud and bare-earth data were assessed to the American Society for Photogrammetry and Remote Sensing Positional Accuracy Standards for Digital Geospatial Data (
Gaps between the 2017 bathymetry and 2018 lidar datasets were inevitable in shallow regions of the reservoir where the multibeam vessel was incapable of accessing and lidar could not penetrate the water surface. Interpolation errors in the TBDEM appear at the location of those gaps because of a lack of topographic or bathymetric data. To create a continuous surface, the gaps were seamlessly assimilated with the U.S. Geological Survey Coastal National Elevation Database methodology of interpolation (
The 2017 bathymetry and 2018 lidar topography do not always overlap or abut. Sizeable gaps between the datasets were filled with interpolated topography to create a continuous surface. The edges of the bathymetry and lidar topography were converted to points and then interpolated within the gaps at a 33-ft (10-m) cell size using ArcGIS Topo to Raster. This methodology was primarily utilized in the northeast region of the dataset.
The datasets and methods used to calculate elevation-area-capacity relationships in Lake Powell are described in this section. The TBDEM created by
The assimilation of interpolated data, incorporation of historical data, and hydro-flattening technique into the TBDEM provides the topobathymetric surface in the absence of data but will cause inconsistencies with the true bathymetric surface that are difficult to quantify. Though these inconsistencies may misrepresent a small fraction (less than 10 percent) of the total TBDEM area, these regions are expected to have the largest volumetric change due to sedimentation at the river deltas. In context of extensive sedimentation observed in the Colorado and San Juan River deltas and inflows (
1. Datasets incorporated into the modified topobathymetric digital elevation model
[mi2, square miles; USGS, U.S. Geological Survey; m, meters; DEM, digital elevation model; USGS, U.S. Geological Survey; Reclamation, Bureau of Reclamation; UDNR, Utah Department of National Resources; NPS, National Park Service; UGRC, Utah Geospatial Resource Center; n/a, interpolated data does not have acquisition date]
Data source | In-text reference | Source | Data type | Year(s) acquired | Published resolution | Coverage |
Lake Powell Arizona-Utah bathymetry | USGS | Multibeam bathymetry | 2017 | 2 m | 129.6 | |
Lake Powell Arizona-Utah lidar | Reclamation | Topographic lidar | 2018 | 1 m | 150.3 | |
Pre-Dam Lake Powell DEM | Reclamation/USGS | Historical DEM | 1947, 1959 | 2 m | 19.1 | |
Lake Powell TBDEM, hydro-flattened | USGS | Hydro-flattened | n/a | 10 m | 3.3 | |
Modified TBDEM, filled sinks | USGS | Void fill areas | n/a | 2 m | 3.0 | |
Colorado, Green, Yampa River lidar | UDNR/NPS | Topographic lidar | 2015 | 0.5 m | 4.8 | |
Utah statewide auto-correlated DEM | UGRC | Topographic lidar | 2006 | 5 m | 2.9 |
Regions of the topobathymetric data that incorporated the historical DEM were modified with a reasonable expectation of sedimentation in Lake Powell. In many places in the reservoir, particularly where steep cliffs are predominant, the historical DEM was an acceptable substitution for data gaps. In other regions, with shallower topography or near the river deltas, the historical DEM does not account for large volumes of accumulated sediment. Steep, sharp drop-offs at the interface between bathymetry and lidar data are most pronounced at the edges of the thalweg where the reservoir narrows into the river channel, creating artifact trenches nearly 165 ft deep where they are, in fact, filled with reservoir sediment. To create a surface that best represents the topography in these areas, these artifacts were individually identified in the delta regions and filled using the Fill tool in ArcMap (version 10.6.1;
Select locations in Lake Powell that highlight modifications made on the topobathymetric digital elevation model (TBDEM;
4. Graphs showing select locations in Lake Powell that highlight modifications made on the topobathymetric digital elevation model
Two substitute elevation datasets were incorporated into the modified TBDEM to replace the zones in the original TBDEM where the river thalwegs are represented with a hydro-flattened elevation value of 3,612.76 ft above NAVD 88 (
Using the TBDEM spatial metadata as a mask to exclude areas where modifications were not necessary (
Elevation-area-capacity relationships were derived from a script written in the Python coding language (Python Software Foundation, Python Language Reference, version 2.7, available at
Units of the original TBDEM (
Resulting 0.33-ft (0.10-m) relationships were used to generate elevation-area-capacity values at 0.01-ft increments by linearly interpolating values between each 0.33-ft (0.10-m) incremental pair. The 0.01-ft interpolated interval was calculated at the request of Reclamation.
Additional storage capacity calculations were done for error assessment at matching 0.01-ft increments for lower (3,160.00–3,161.00 ft above NAVD 88), middle (3,400.00–3,401.00 ft above NAVD 88), and upper (3,700.00–3,711.00 ft above NAVD 88) elevations. Values were generated following the same procedures outlined for the original 0.33-ft (0.10-m) increment calculations, thereby providing a one-to-one comparison dataset against the linearly interpolated values for these discrete elevation bands.
The TBDEM is referenced to the NAVD 88 using the Geoid12B geoid and horizontally referenced to the North American Datum of 1983 with the National Adjustment of 2011, UTM Zone 12 projection (
This section details elevation-area-capacity relationships in Lake Powell derived from the 2017–18 reservoir survey, along with associated low, middle, and high elevation band error assessment results. These results are compared with previously published estimates of storage capacity and areal extent of Lake Powell by Bureau of
Results from the 2017–18 survey indicate that the total storage capacity and areal extent at full pool (3,702.91 ft above NAVD 88) are 25,160,000 acre-feet and 159,200 acres, respectively. These values represent a decrease in storage capacity of 1,833,000 acre-feet or 6.79 percent from 1963 to 2018 and a 1,048,000 acre-ft or 4.00 percent decrease from 1986 to 2018. The decrease in areal coverage is 2,142 acres or 1.33 percent from 1963 to 2018 and 1,536 acres or 0.96 percent from 1986 to 2018. The elevation-area-capacity relationships are summarized in
2. Summary of previous and current elevation-area-capacity relationships in Lake Powell (including benchmark elevations)
[ft, feet; NGVD 29, National Geodetic Vertical Datum of 1929; NAVD 88, North American Vertical Datum of 1988; acre-ft, acre-feet; n/a, area and storage capacity for given elevation are not published]
Elevation |
Elevation (ft) |
19631 | 19862 | 2017–183 | Loss of capacity, 1963–2018 |
Percentage of capacity at full pool5 | |||
Area |
Storage capacity |
Area |
Storage capacity |
Area |
Storage capacity |
||||
3,700 | 3,702.91 | 161,390 | 27,000,000 | 160,784 | 26,214,861 | 159,248 | 25,166,112 | 6.79 | 100.00 |
3,680 | 3,682.91 | 147,490 | 23,914,000 | 145,647 | 23,150,551 | 144,148 | 22,128,694 | 7.47 | 87.93 |
3,660 | 3,662.91 | 134,280 | 21,097,000 | 130,899 | 20,385,098 | 130,204 | 19,389,066 | 8.10 | 77.04 |
3,640 | 3,642.91 | 121,510 | 18,540,000 | 118,054 | 17,895,574 | 117,446 | 16,912,555 | 8.78 | 67.20 |
3,620 | 3,622.91 | 109,690 | 16,229,000 | 105,929 | 15,655,745 | 103,666 | 14,700,802 | 9.42 | 58.42 |
3,600 | 3,602.91 | 98,470 | 14,148,000 | 95,387 | 13,642,587 | 90,587 | 12,770,822 | 9.73 | 50.75 |
3,580 | 3,582.91 | 88,150 | 12,284,000 | 85,667 | 11,832,048 | 80,358 | 11,064,223 | 9.93 | 43.96 |
3,560 | 3,562.91 | 78,810 | 10,616,000 | 75,981 | 10,215,568 | 71,295 | 9,548,005 | 10.06 | 37.94 |
3,540 | 3,542.91 | 69,700 | 9,133,000 | 67,206 | 8,783,697 | 63,339 | 8,202,881 | 10.18 | 32.59 |
3,520 | 3,522.91 | 61,750 | 7,820,000 | 59,476 | 7,516,870 | 56,052 | 7,009,771 | 10.36 | 27.85 |
3,500 | 3,502.91 | 54,790 | 6,656,000 | 52,386 | 6,398,246 | 49,057 | 5,959,757 | 10.46 | 23.68 |
3,490 | 3,492.91 | 51,600 | 6,124,000 | n/a | n/a | 45,864 | 5,485,084 | 10.43 | 21.80 |
3,480 | 3,482.91 | 48,590 | 5,623,000 | 46,275 | 5,411,639 | 43,040 | 5,041,128 | 10.35 | 20.03 |
3,460 | 3,462.91 | 42,110 | 4,717,000 | 40,361 | 4,545,281 | 37,852 | 4,232,898 | 10.26 | 16.82 |
3,440 | 3,442.91 | 35,830 | 3,938,000 | 34,699 | 3,794,678 | 32,902 | 3,526,543 | 10.45 | 14.01 |
3,420 | 3,422.91 | 30,650 | 3,275,000 | 30,045 | 3,147,240 | 28,472 | 2,914,717 | 11.00 | 11.58 |
3,400 | 3,402.91 | 26,680 | 2,704,000 | 26,062 | 2,586,177 | 25,019 | 2,378,132 | 12.05 | 9.45 |
3,380 | 3,382.91 | 22,480 | 2,213,000 | 22,102 | 2,104,540 | 20,442 | 1,927,743 | 12.89 | 7.66 |
3,370 | 3,372.91 | 20,640 | 1,998,000 | n/a | n/a | 18,915 | 1,731,287 | 13.35 | 6.88 |
3,360 | 3,362.91 | 18,970 | 1,800,000 | 18,504 | 1,698,475 | 17,424 | 1,550,496 | 13.86 | 6.16 |
3,340 | 3,342.91 | 15,990 | 1,452,000 | 15,698 | 1,356,447 | 15,124 | 1,225,879 | 15.57 | 4.87 |
3,320 | 3,322.91 | 13,870 | 1,155,000 | 13,603 | 1,063,436 | 13,129 | 941,803 | 18.46 | 3.74 |
3,300 | 3,302.91 | 12,110 | 897,000 | 11,906 | 808,350 | 11,482 | 696,244 | 22.38 | 2.77 |
3,280 | 3,282.91 | 10,490 | 671,000 | 10,299 | 586,303 | 9,240 | 484,015 | 27.87 | 1.92 |
3,260 | 3,262.91 | 8,460 | 482,000 | 8,044 | 402,872 | 7,592 | 318,506 | 33.92 | 1.27 |
3,240 | 3,242.91 | 6,960 | 329,000 | 6,752 | 254,905 | 6,148 | 180,056 | 45.27 | 0.72 |
3,220 | 3,222.91 | 5,600 | 203,000 | 5,114 | 136,241 | 3,910 | 77,944 | 61.60 | 0.31 |
3,200 | 3,202.91 | 4,100 | 106,000 | 3,381 | 51,290 | 2,013 | 15,199 | 85.66 | 0.06 |
3,180 | 3,182.91 | 2,370 | 42,000 | 1,249 | 4,995 | 76 | 3,199 | 92.38 | 0.01 |
3,160 | 3,162.91 | 1,050 | 8,000 | 0 | 0 | 0 | 0 | 100.00 | 0.00 |
From Bureau of
From
Calculated from modified topobathymetric digital elevation model (TBDEM;
Percent change in storage capacity from 1963 to 2017–18 surveys.
Percent of current storage capacity at full pool for a given elevation according to the 2017–18 TBDEM.
Storage capacity (bottom axis, black lines) and areal extent (top axis, blue lines) of the reservoir calculated from the modified topobathymetric digital elevation model (
5. Graph showing storage capacity and areal extent of the reservoir calculated from modified topobathymetric digital elevation model at 0.1-meter intervals
Difference in storage capacity by
6. Graphs showing the difference in storage capacity by absolute volume and percent from 1963 and 1986 to 2018
Error analysis of the interpolated relationships was performed at 0.01-ft intervals across three elevation bands: (1) lower (3,160.00–3,161.00 ft above NAVD 88); (2) middle (3,400.00–3,401.00 ft above NAVD 88); and (3) upper (3,700.00–3,711.00 ft above NAVD 88). The interpolated values are comparable to the calculated values, with differences ranging from −0.01 to 0.03 percent and 0 to 0.02 percent for area and storage capacity calculations, respectively. The error analysis for all interpolated values is available for download at
Intermediate reservoir elevations include critical benchmarks for the management of Lake Powell and operations at Glen Canyon Dam. The dead storage elevation (3,372.91 ft above NAVD 88), which is the reservoir level below all hydroelectric penstocks and other outlet works, has decreased in storage capacity by 152,900 acre-feet or 8.11 percent from 1963 to 2018 and 27,100 acre-feet or 1.54 percent from 1986 to 2018. The inactive storage level (up to 3,492.91 ft above NAVD 88) represents the lowest reservoir elevation that all hydroelectric penstocks are submerged. Storage capacity at the inactive storage level has decreased by approximately 599,900 acre-feet or 9.84 percent from 1963 to 2018 and 333,000 acre-feet or 5.72 percent from 1986 to 2018.
These results reflect the elevation-area-capacity relationships determined in this study and are not directly comparable to values used for operations at Glen Canyon Dam. Direct comparisons to Reclamation operational relationships are outside the scope of this report.
Sources of error in the TBDEM and elevation-area-capacity calculations are difficult to identify and quantify. Random errors in topographic and bathymetric surveying are small and are ignored here. Systematic errors are difficult to identify, though each dataset was independently assessed for error prior to being assembled into the TBDEM. Interpolation errors are quantifiable, but this was not calculated because of the number of datasets and range of acquisition dates for each survey.
Because the TBDEM comprises sources with different resolutions, coverages, and known errors, the vertical error can be reasonably quantified. The data sources that most represent the TBDEM by area are the 2017 bathymetry (
Between 1963 and 2018, the average annual loss in storage capacity was approximately 33,270 acre-feet per year. Deposition at the deltas of the sediment-laden Colorado and San Juan Rivers is the primary cause of storage loss in Lake Powell (Bureau of
Advancements in bathymetric survey technology over time has allowed for greater spatial coverage, accuracy, and density of bathymetric data which reduces the need to interpolate over large survey errors in the final DEM. The range-line (Bureau of
As a first-order approximation, the average annual loss of storage loss in Lake Powell indicates the remaining volume at full pool will be filled in approximately 750 years. However, the reservoir fills laterally, from the deltas toward Glen Canyon Dam, and would likely cease to be useful sooner. Estimating the remaining useful life of Lake Powell is multifaceted and beyond the scope of this study. This approximation would need to include accounting for benchmark elevations at Glen Canyon Dam, dynamic river discharge and sedimentation rates, the spatial distribution of sediments, climate sensitivity, and potential sediment mitigation activities such as dredging.
The distribution of absolute storage-capacity change since 2018 at reservoir elevations is not linear, with the greatest changes in storage capacity observed in elevations ranging between approximately 3,250–3,350 and 3,600–3,700 ft above NAVD 88 (
The completion of Glen Canyon Dam by the Bureau of Reclamation (Reclamation) in 1963 created Lake Powell and provided the means to supply water to a growing population in the American southwest. A bathymetric survey of the reservoir was completed in 1986 to measure the change in storage capacity since impoundment. In 2017 and 2018, the U.S. Geological Survey and Reclamation completed extensive surveys of the reservoir utilizing high-resolution multibeam bathymetry and lidar. These data were merged into a seamless topobathymetric dataset, which was subsequently revised to calculate new elevation-area-capacity relationships. This collaborative effort provides a revised and high-resolution estimate of storage capacity in Lake Powell and an updated topobathymetric surface to support water availability studies amidst prolonged drought. The preceding report summarizes the updated elevation-area-capacity relationships, describes the surveying methods and elevation-area-capacity calculations, and provides comparisons of the updated elevation-area-capacity relationships with previous estimates.
Storage capacity and areal extent of Lake Powell was determined for a range of elevations from 3,120 to 3,717.20 ft above the North American Vertical Datum of 1988 (NAVD 88). The updated elevation-area-capacity relationships indicate Lake Powell has lost 1,833,000 acre-feet or 6.79 percent of its storage capacity at full pool (3,702.91 ft above NAVD 88) since construction was completed in 1963 through 2018. With consideration to potential error in the topobathymetric dataset, the loss of storage capacity ranges between 1,607,000 and 2,059,000 acre-feet. The reduction in storage capacity is attributed to sedimentation at the deltas of the Colorado and San Juan Rivers. Decreases in storage capacity were largest for the reservoir at elevations above 3,600 ft above NAVD 88, which coincide with frequent reservoir elevations since the 1970s. Historical surveys were limited by comparatively coarser survey techniques than those used for the 2017–18 topobathymetric digital elevation model, though the average annual storage loss between surveys remained similar since impoundment in 1963. With increasing demands on water in the Colorado River Basin amidst a decadal-scale drought, these results provide critical information to support water resource management in Lake Powell and beyond.
This range of reservoir elevations, from 1,064.6 to 1,128.65 meters (3,492.91–3,702.91 feet), represents the levels that all penstocks and river outlets at Glen Canyon Dam are submerged.
Software developed by the Bureau of Reclamation to determine elevation-area-capacity relationships that are independent from the results in this report.
Methodology for developing TBDEMs that assimilates topographic and bathymetric data sources into a seamless surface.
Datasets published prior to 1988 are originally referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29); for clarity, all elevations have been converted to the North American Vertical Datum of 1988 (NAVD 88), unless otherwise noted, with a conversion factor of +0.887 meter (2.91 feet) from NGV29 to NAVD 88.
This benchmark elevation, at 1,028.06 meters (3,372.91 feet), represents the lowest level that water can be released through Glen Canyon Dam.
The cumulative areal extent and storage capacity, or volume, at a given reservoir elevation.
As Glen Canyon Dam crests at 1,133.22 meters (3,717.91 feet), all reservoir levels above 1,128.65 meters (3,702.91 feet) are considered a risk to overflowing the dam.
Hydro-flattening is post-processing of topographic data to reflect flat-water surfaces. In this report, the regions of the topobathymetric digital elevation model that are active rivers (that is, upstream from the surveyed reservoir but within the reservoir limits) were hydro-flattened and do not reflect the river gradient.
This range of reservoir elevations, from 1,028.06 to 1,064.6 meters (3,372.91–3,492.91 feet), represents the levels that penstocks and river outlets at Glen Canyon Dam begin to be subaerially exposed and limit generation of hydroelectric generation.
A DEM derived from pre-Glen Canyon Dam topographic surveys in 1947 for the San Juan River arm and 1959 for the Colorado River arm.
A form of bathymetric surveying that consisted of measuring existing sediment profiles with an echosounder, typically from bank to bank in a reservoir.
The expected amount of time a reservoir can reasonably maintain its ability to functionally store water.
The rate that sediment is deposited as a volume or mass per unit time. This report does not investigate sediment or modes of sedimentation and referencing loss of storage capacity as a sedimentation rate is not advised.
A tool packaged with the Spatial Analyst Supplemental Toolbox for ArcGIS by Esri. This tool creates a table of surface area and storage capacity, or volume, for an input surface raster at desired elevations. The script was modified for use on the Yeti supercomputer.
An integrated, multi-source dataset of topographic and bathymetric elevation data.
High-performance computing cluster at the U.S. Geological Survey Advanced Research Computing in Denver, Colorado, that was used to calculate the elevation-area-capacity relationships for Lake Powell.
For more information concerning the research in this report, contact the
Director, Utah Water Science Center
U.S. Geological Survey
2329 West Orton Circle
Salt Lake City, Utah 84119-2047
801-908-5000
Publishing support provided by the U.S. Geological Survey
Science Publishing Network, Sacramento Publishing Service Center