Bathymetry, topography, and sediment grain-size data from the Elwha River delta, Washington, July and August, 2023

Two dams on the Elwha River, Washington State, USA trapped over 20 million m3 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. Surveys of nearshore bathymetry, beach topography and surface sediment grain size from the Elwha River delta, Washington were conducted between July 30 and August 2, 2023 (USGS Field Activity Number 2023-645-FA) by a team of scientists from the U.S. Geological Survey Pacific Coastal and Marine Science Center (PCMSC), Washington State Department of Ecology (WA DOE), and Washington Sea Grant. Nearshore bathymetry data were collected using two personal watercraft (PWCs) and a kayak, each equipped with single-beam echosounders and survey-grade global navigation satellite systems (GNSS). Topography data were collected on foot with GNSS 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 172 km of nearshore bathymetric survey lines and 152 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. Surface sediment was sampled using a small ponar, or 'grab', sampler on July 30, 2023 from the R/V Dogfish at a total of 76 locations in water depths between about 1 and 17 m around the delta. An additional 18 sediment samples were collected on August 2, 2023 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 this smaller region. This data release is part of a collection. Visit the following website to access additional topographic, bathymetric, and surface-sediment grain size datasets collected on the Elwha River: https://doi.org/10.5066/F72N51GC.