Topobathymetric elevation model of the causeway breach, Great Salt Lake, Utah

A permeable rock-fill causeway was constructed across Great Salt Lake between 1957–1959, dividing the lake into North and South Arms. Several open channels have been constructed to connect the two arms of the lake, with the most recent, informally named the New Breach, being completed in 2016. A berm across the New Breach restricts flow between the North and South Arms and was originally built to 4,183 feet above the National Geodetic Vertical Datum of 1929 (NGVD29, in accordance with historical elevation records at Great Salt Lake). However, due to increasing salinity and low water-surface elevation and volume in the South Arm, water managers raised the berm in July 2022 to 4,187 feet above NGVD29 and again in February 2023 to 4,192 feet above NGVD29 to capture freshwater in the South Arm and maximize dilution of salinity. Elevation data were collected through the breach and adjacent areas after the berm was raised in 2023 to monitor changes in berm geometry and surrounding channel bathymetry. A seamless topobathymetric digital elevation model was assimilated using drone-derived topography and acoustic doppler current profiler (ADCP) bathymetry. Surface and shallow topography were surveyed by drone photogrammetry on October 19, 2023 and August 14, 2024. A handheld real-time kinematic (RTK) global navigation satellite system (GNSS) receiver, consisting of a base-station receiver referenced over a known point and elevation and a mobile-station receiver, collected single-point elevation data in the survey area including across the partially submerged berm. The RTK data provides an independent measure of elevation to assess the photogrammetric digital elevation model (DEM) for horizontal or vertical error and to build a simple regression for calibrating the submerged topography. This regression for submerged topography is limited to shallow, clear water in parts of the breach with laminar flow where an RTK measurement could be safely made. Because the berm was partially eroded and submerged during surveying activities, only the drone-derived DEM could show the character of erosion in the berm and provide accurate estimates of topography. The management berm eroded from the as-built elevation of 4,192 feet to approximately 4,187 feet, at its lowest point across the breach, between its construction on February 10, 2023, and October 19, 2023. The vertical error subaerial topography is less than one centimeter (cm); for submerged regions across the berm only, the median error estimate is 3.01 cm.

This data release will be updated as additional photogrammetric and bathymetric surveys are collected and processed. All additions and changes are recorded in Great_Salt_Lake_Breach_ChangeLog.txt.