NV5 provided geotechnical consultation for emergency spillway repairs at Lake Van Norden near Donner Summit.
NV5 staff initially visited the site and observed a large crack, approximately 15 to 18 feet long and up to 6 feet wide at the northeast end of the spillway. Water had undermined the concrete, causing erosion of the supporting soil and creating a 6-foot-deep void below the concrete apron. A portion of the concrete spillway apron had broken and had fallen into the void. We met with the local land owner, the repair contractor, and a representative of the State of California’s Division of Safety of Dams (DSOD) to evaluate and decide on a temporary repair strategy given the onset of winter at this high elevation site. A temporary plan was provided to DSOD; it was approved and the plan implemented prior to the first snow storm.
NV5 then returned to the site and used digital instrumentation to perform a hydrographic survey of the lake in an effort to determine which areas would be impacted by a potential drawdown of the lake level during dam and spillway repairs. To reduce impacts to local homeowners around the lake, we developed a long-term repair approach to the spillway that avoided drawdown of the lake, yet met with DSOD approval. The repairs were made, and DSOD continued to work with the land owner regarding additional permit issues for the dam.