Chelan County PUD has operated Rock Island Dam on the Columbia River since 1933. The District retained NHC in 2008 and again in 2018 to perform hydrographic surveys and evaluate the tailrace below the dam as part of its long-term monitoring program. The 2018 project included four primary elements: 1) establishment of horizontal coordinate system and vertical datum with conventional terrestrial RTK GPS methods; 2) bathymetric survey with boat mounted multi-beam eco-sounder (MBES); 3) three-dimensional CAD modelling to represent portions of the dam structure; and 4) assessment of changes in the riverbed and identification of locations of interest for future monitoring of potential scour based on comparison of 2018 and 2008 bathymetry. NHC worked closely with District staff before and during the survey and provided recommendations for future monitoring activities. This project resulted in important documentation and guidance for the District’s ongoing monitoring program of this piece of regionally important infrastructure.