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Lower Elwha River, Ground-Based Lidar Fly-Through

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Uploaded on Jan 31, 2012

http://gallery.usgs.gov/videos/517

This video shows a virtual fly-through of a detailed, highly accurate three-dimensional model of the lower Elwha River, Washington. The video begins about 0.8 river kilometers upstream (south) of the bridge on Elwha River Road. The virtual flight path then proceeds downstream approximately 5.5 kilometers, in a northerly direction to the mouth of the river on the Juan de Fuca Strait.

The data that are shown in the fly-through are a composite of multiple scans that were collected with a ground-based lidar (light detection and ranging) scanner, which uses high-speed laser measurements to produce highly accurate three-dimensional maps of the riparian environment. By combining these measurements with digital images from an onboard camera, the instrument produces three-dimensional "point clouds" that can be displayed in true color. Because the water surface is not measured by the lidar scanner, it appears black in the video. Each of the millions of data points represents a discrete measurement with precise elevation and geographic position. Cobble bars, gravel beds, bluffs, riverside vegetation and man-made features are all visible in the data. Each feature can be queried for size, geographic position and precise elevation.

The river system shown in this video is downstream from the Elwha and Glines Canyon Dams, both of which are being removed in the largest dam removal project in U.S. history. For nearly a century, these dams have been preventing salmon and steelhead from accessing historic spawning habitat above the dams. The dams have also been blocking the natural supply of sediment to the lower river, and the nearby coastal beaches. Beginning in 2006, scientists from the United States Geological Survey (USGS) have been monitoring seasonal changes in the river channel below the dams to serve as a baseline with which to compare post-dam-removal changes in the future. As part of the last survey before dam removal began in September 2011, scientists from the USGS conducted the ground-based lidar survey to accurately map the lower river in great detail. This data set will be compared with measurements from future surveys to monitor and quantify changes that occur in the river system after the two dams have been removed.

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