Earthshots: Satellite Images of Environmental Change

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» Lake Powell, Utah and Arizona, USA

Glen Canyon Dam on the Colorado River was completed in 1963. It created Lake Powell, which ebbs and flows depending on upstream precipitation. Lately, it’s been more ebb.

Glen Canyon National Recreation Area encompasses Lake Powell and is visited by more than 2 million people per year.

Since 2000, the Colorado River Basin has been in an extended drought. During the period 2000–2018, the inflow of water into Lake Powell was above average in only 4 years. As a result, Lake Powell was at less than half capacity in January 2019.

Droughts combined with a rising population means water sustainability will only become more of a challenge. In addition, hydropower capacity at Glen Canyon Dam could be reduced. Severe droughts are a regular part of the climate variability in this region; however, droughts are expected to become more severe in the future.

This study is just one example of researchers finding that extreme, prolonged droughts are expected in the U.S. Southwest throughout this century.

Map of the featured area.

Drought combined with water withdrawals has caused a drop in the lake’s water level. The reservoir finished filling in 1980. The highest water level recorded was in July 1983. The lowest was in October 2004. As of January 2019, the lake’s level is down over 100 feet from its high mark.

On the chart, the numbers on the left indicate feet above sea level for the lake’s water level. A water level of 3,700 feet is the reservoir at full capacity.


Lake Powell Historical Water Level Data

Water level data for Lake Powell. Source: U.S. Bureau of Reclamation.

Source: U.S. Bureau of Reclamation.

Glen Canyon Dam near Page, Arizona, creates Lake Powell. The 710-foot-high dam was completed on September 13, 1963, about 9 years before the first clear Landsat 1 images were acquired. The dam also generates electricity. From 1980 to 2013, its average annual gross electricity generation was about 5 billion kwh. (kwh = kilawatt-hours, a measure of a power station’s electricity output.) Its electricity generation varies based on the amount of water that flows into the lake, which is influenced by precipitation.

In the Landsat series of images shown here, we begin with 1972 when the lake was still filling. In 1984, the lake was at one of its highest water levels.

Near the dam is the city of Page, Arizona, which began in 1957 as a housing camp for workers building the dam. Page is now a major resort area. Its 2017 population was 7,553.

At various marinas on the lake, tourists can rent houseboats and other recreational watercraft. Wahweap is the largest marina on Lake Powell. This marina needs to move based on the lake’s water level. Antelope Point is the newest marina on Lake Powell, established in 2004.

Antelope Island is in the center of these images. It looks a lot less like an island in the later low water level images. The National Park Service dug a channel on the island’s north end called Castle Rock Pass. Even though it begins to look more like a peninsula by the 2005 image, it is still called Antelope Island. The channel around the north side of the island is navigable when the lake’s water level is 3,620 feet or higher.

Comparing the 1984 (high water level) and 2005 (low water level) images, there is a pale outline along many parts of the lake. When the water level drops, canyon walls that were once inundated are exposed again.

Referred to as the “bathtub ring,” this pale outline shows when the lake is below capacity. Calcium carbonate and other mineral compounds, many of them various salts in the water, attach themselves to the sandstone and leave behind this white mark. The top of the white mark is the high water mark. The only time the bathtub ring is not visible is when the lake is completely full.

Farther upstream, the San Juan River flows into the Colorado River. In these narrower upstream portions of the rivers, more exposed riverbed appears in the later images.

While the other series of images at this page do not show very much difference between the 2005 and 2018, upstream areas of the reservoir have shrunk or gotten much shallower. Follow the San Juan River upstream, and it becomes less dark in 2015. Shallower water has more sediment and that appears lighter.


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