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. Survey operations were conducted between September 16 and September 19, 2013 (USGS Field Activity Number W-07-13-PS) by a team of scientists from the U.S. Geological Survey Pacific Coastal and Marine Science Center (PCMSC) and Eastern Geographic Science Center (EGSC), Washington State Department of Ecology (WA DOE), and Washington Sea Grant.
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 130 km of nearshore bathymetric survey lines and 130 km of topographic survey lines were collected during the 4 days of survey operations. Environmental conditions were favorable, resulting in excellent coverage of the beach and nearshore region achieved using the combination of methods described above. Surface sediment was sampled using a small ponar, or 'grab', sampler on September 19, 2013 from the R/V Frontier at a total of 62 locations in water depths between about 1 and 12 m around the delta. An additional 21 sediment samples were collected between September 16 and September 19, 2013 at low tide from intertidal locations on the delta. A handheld GNSS receiver was used to determine the locations of sediment samples. 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.