WORLD FROM SPACE - Elwha River, Washington, USA

The Elwha River arises from headwaters in the Olympic Mountains and flows northward across Washington, emptying into the Strait of Juan de Fuca. In the early twentieth century, Thomas Aldwell—a politician, banker, and entrepreneur—saw an opportunity in the river’s rapid waters and narrow gorges. He decided to harness the river’s energy and secured enough investment money to establish the Olympic Power Company.

In 1910, construction began on the Elwha Dam, which began generating hydropower in 1913. In the 1920s, the region's growing economy prompted the construction of another dam in the Glines Canyon, several miles upstream. The dams fueled economic development but came with costs. Because they lacked fish ladders, the Elwha and Glines Canyon dams stopped the migration of fish upriver for spawning. Salmon and steelhead, which had once been abundant along the Elwha, all but disappeared above the Elwha Dam. These fish species had provided food for more than 100 other wildlife species along the river.

The dams also changed the landscape. The construction of the Elwha Dam created Lake Aldwell, and the Glines Canyon Dam created Lake Mills. These reservoirs held back not just water but also sediment. The trapped sediment could no longer replenish the riverbanks and coastline downstream.

Several decades after the dams were built, their drawbacks prompted a decision by the Department of the Interior to remove them. The project comprised the largest dam removal in U.S. history.

The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured these natural-color images of Lake Aldwell on August 10, 2004 (top), and May 12, 2012 (bottom). These images have been rotated so that north is to the lower right. Removal of the Elwha Dam started in September 2011 and concluded in March 2012. The high-resolution images also show changes in Lake Mills and the Glines Canyon Dam, which is expected to be completely removed by the summer of 2013.

Restoring the Elwha River entails more than tearing down hydroelectric dams. It also entails reintroducing fish and plant species—projects partially completed by the time ALI acquired the later image.

One of the biggest changes is likely to result from releasing sediment trapped in the reservoirs. The Elwha and Glines Canyon dams trapped an estimated 19 million cubic meters of sediment. In addition to being the largest dam removal in U.S. history, the project along the Elwha is also the biggest controlled sediment release. Researchers with the U.S. Geological Survey forecast that removal of the dams would release 7 to 8 million cubic meters of sediment downstream. In fact, removal of the dams proceeded at a measured pace in order to prevent the release of too much silt, clay, and sand too quickly.

Not all of the sediment was expected to leave the reservoir beds, and the material left behind was to be planted with native species. So the image from 2012 shows a work in progress. The reservoir had largely drained, but the sediment was still barren and awaiting replanting.

NASA Earth Observatory image created by Jesse Allen and Robert Simmon, using Advanced Land Imager data from the NASA EO-1 team. Caption by Michon Scott. Instrument: EO-1 - ALI