AN ANALYSIS OF SEDIMENTS IMPOUNDED AT GOLD RAY DAM, JACKSON COUNTY, OREGON: INITIAL STEPS IN REMOVAL OF A MAINSTEM DAM

We have completed an assessment of sediment impounded behind Gold Ray Dam as part of a feasibility study on potential dam removal. Gold Ray Dam is a mainstem dam on the Rogue River in Jackson County, Oregon. Originally built as a log crib dam in 1903 for the purposes of electrical generation, the present concrete structure was erected in 1941 and abandoned in 1972. Ownership of the dam was transferred at that time to Jackson County, the current owner of the property. The dam is a significant barrier to salmonid migration and a liability to the County, which seeks the dam’s removal. We have determined the volume, aerial extent, and textural nature of the sediments impounded behind Gold Ray Dam. Approximately 400,000 cubic yards of sediment are currently deposited in a slack-water area immediately upstream of the dam, with an additional 1,800,000 cubic yards deposited in a wetland/slough complex. Twelve vibracores were collected from the Gold Ray Reservoir to assess grain size and distribution of sediments in the main channel and inundated backwater environments (sloughs). Sediment composition in the main channel of the Rogue River is primarily sand and gravel; sediment located in the sloughs is composed primarily of silt and clay. The overall volume of sediment calculated for Gold Ray Dam is surprisingly small given annual sediment loads of approximately 100,000 cubic yards/year for downstream reaches of the Rogue River near Savage Rapids Dam. The results of this study will be used to construct transport models that will assess sediment mobility if Gold Ray Dam is removed.