Two dams on the Elwha River, Washington State, USA trapped over 20 million cubic meters of sediment, reducing downstream sediment fluxes and contributing to erosion of the river's coastal delta. The removal of the Elwha and Glines Canyon dams between 2011 and 2014 induced massive increases in river sediment supply and provided an unprecedented opportunity to examine the response of a delta system to changes in sediment supply. The U.S. Geological Survey (USGS) developed an integrated research program aimed at understanding the ecosystem responses following dam removal. The research program included repeated surveys of beach topography, nearshore bathymetry, and surface sediment grain size to quantify changes in delta morphology and texture following the dam removals. For more information on the USGS role in the Elwha River Restoration Project, please visit http://walrus.wr.usgs.gov/elwha/.
This USGS data release presents data collected during surveys of nearshore bathymetry, beach topography, and surface sediment grain size from the Elwha River delta, Washington. Bathymetry and topography data were collected between April 26 and April 29, 2014, and surface sediment samples were collected on May 12, 2014 (USGS Field Activity Number 2014-620-FA). The survey team included scientists from the U.S. Geological Survey Pacific Coastal and Marine Science Center (PCMSC), Washington State Department of Ecology (WA DOE), Washington Sea Grant, and University of Washington.
Nearshore bathymetry data were collected using two personal watercraft (PWCs), each equipped with single-beam echosounders and survey-grade global navigation satellite system (GNSS) receivers. Topography data were collected on foot with GNSS receivers mounted on backpacks. Positions of the survey platforms were referenced to a GNSS base station placed on a nearby benchmark with known horizontal and vertical coordinates. Depths from the echosounders were computed using sound velocity profiles measured with a conductivity-temperature-depth (CTD) sensor during the survey. A total of 150 km of nearshore bathymetric survey lines and 130 km of topographic survey lines were collected during the 4 days of survey operations. Swift currents resulting from high river discharge during the survey limited access to portions of the river mouth that have normally been sampled by topographic surveyors on foot. Despite the challenge of high river flow, good coverage of the beach and nearshore region was achieved using the combination of methods described above. Surface sediment was sampled using a small ponar, or 'grab', sampler on May 12, 2014 from a small boat at a total of 43 locations in water depths between about 1 and 12 m around the delta. A continuous DEM surface of the primary survey area was produced from all available bathymetry and topography data using linear interpolation and a grid-spacing of 5 m. An additional DEM with 1-m resolution grid-spacing was produced using linear interpolation for a smaller region adjacent to the river mouth.
Digital files containing the nearshore bathymetry data, beach topography data, derived DEMs, and grain-size data from this survey are available for download from the child item pages.