River-channel topography on the Elwha River, Washington, 2006 to 2017

Abstract

This portion of the data release presents topographic data collected at 5 study sites along Elwha River, Washington between 2006 and 2017. Elevations along channel-perpendicular transects were surveyed using a total station and prism rod. Initial geodetic control was established using static global positioning system (GPS) occupations. A total station was subsequently used to expand and maintain the survey control network at each site. All survey data were referenced to the NAD83 datum, using the UTM, zone 10, coordinate reference system. All elevations were referenced to the NAVD88 vertical datum. Based on repeat measurements of points with known positions, we estimated the horizontal and vertical accuracy of the topographic measurements to be within 2 to 3 cm. Topographic data were collected using a total station using survey layout routines to locate data along the same transects during each survey. Wetted portions of the channel were measured primarily by wading with the survey rod. In several locations where wading was not feasible due to water depth, measurements were not taken or they were made by swimming with the survey rod or by deploying the survey rod from an inflatable kayak (necessary in the thalweg of reach 3 between 2006 and 2011). Although the focus of the surveys was to make repeated measurements of elevations along a transect, some additional topographic measurements were within the reaches off of the transects. Additionally, a small side channel within reach 2 was surveyed from 2006 to 2008 along transects perpendicular to that channel and along the channel's thalweg. Two series of figures are provided to aid with visualizing the channel cross-section data. The first series, labeled “Elwha_CrossSectionPlots_FallSurveys_*.png”, shows the channel cross-section profiles from the annual fall surveys, plotted for each transect and each reach. The second series, labeled “Elwha_CrossSectionPlots_Grid_FallSurveys_*.png”, shows the channel cross-section profiles from the annual fall surveys for each reach, with each survey date and transect on a separate set of axes to provide a better means of viewing cross-section changes between survey dates (note that Reach 1B was not plotted this way because it was surveyed less frequently).