Digital elevation models (DEMs) of the Elwha River delta, Washington, July 2015

This part of the data release presents a digital elevation model (DEM) derived from bathymetry and topography data of the Elwha River delta collected in July 2015. 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 developed an integrated research program aimed at understanding the ecosystem responses following dam removal that included regular monitoring of coastal and nearshore bathymetry and topography. As part of this monitoring program, the USGS conducted a bathymetric and topographic survey in the Strait of Juan de Fuca on the Elwha River delta, Washington (USGS Field Activity Number 2015-648-FA). Bathymetry data were collected using two personal watercraft (PWCs), each equipped with single-beam echosounders and survey-grade global navigation satellite systems (GNSS). Topography data were collected on foot with GNSS receivers mounted on backpacks. DEM surfaces were produced from all available elevation data using linear interpolation.本次数据发布的相关内容，包含2015年7月采集的美国华盛顿州埃尔瓦河（Elwha River）三角洲水深与地形数据衍生得到的数字高程模型（Digital Elevation Model, DEM）。此前，美国华盛顿州埃尔瓦河上的两座水坝累计拦蓄泥沙超2000万立方米，降低了下游泥沙输运通量，并加剧了该河滨海三角洲的侵蚀作用。2011至2014年间，埃尔瓦水坝与格莱恩斯峡谷水坝（Glines Canyon Dam）的拆除使得河流泥沙供给量大幅提升，为探究三角洲系统对泥沙供给变化的响应提供了前所未有的研究契机。美国地质调查局（U.S. Geological Survey, USGS）制定了一项综合性研究计划，旨在解析水坝拆除后的生态系统响应，该计划涵盖滨海及近岸区域水深与地形的常态化监测工作。作为该监测计划的组成部分，USGS于2015年在华盛顿州胡安·德富卡海峡（Strait of Juan de Fuca）的埃尔瓦河三角洲区域开展了水深与地形测量作业（USGS野外活动编号：2015-648-FA）。本次水深数据通过两艘个人水上交通工具（personal watercraft, PWCs）采集，每艘均搭载单波束测深仪与测量级全球导航卫星系统（global navigation satellite systems, GNSS）；地形数据则采用背负式GNSS接收机以徒步方式完成采集。研究人员基于所有可用高程数据，通过线性插值法生成了DEM曲面。