DESCRIPTION: Scour occurred beneath the east fish ladder at the Leaburg Dam located on the McKenzie River, east of Leaburg, Oregon. The scour undercut the foundation soil from beneath the west (riverside) portion of the fish ladder. An underwater inspection of the fish ladder was completed by others indicated the scour extended up to ±15 feet horizontally beneath the fish ladder with a vertical void up to ±4.3 feet deep along the west edge of the fish ladder.
SERVICE: Foundation Engineering completed a geotechnical investigation to provide geotechnical consultation associated with the design of scour mitigation. Our work included a site reconnaissance, a review of the available information and exploratory drilling adjacent to the fish ladder. The site is underlain by gravelly soils and shallow bedrock. A number of mitigation options were considered. The selected mitigation involved driving sheet piles around the perimeter of the fish ladder and filling the voids beneath the fish ladder with concrete. We provided design and construction recommendations for the repair and also provided construction observations and on-site consultation during pile driving for a test pile program used to evaluate the attainable penetration depths for the sheet piles.