Folsom Dam Raise, Dikes 1-6

Challenges

Folsom Dam was constructed circa 1950 and consists of a main concrete dam (approximately 280 feet high) and a network of 11 other earthen dikes and dams.  The network of dams and dikes provides flood risk reduction to a population of nearly 500,000 people downstream along the American River.  The U.S. Army Corps of Engineers (USACE) Sacramento District desired to raise the dikes by 3.5 feet, in addition to implementing structural changes to the main dam, to increase the reservoir flood surcharge storage capacity.  The dikes were up to 110 feet high and 2,000 feet long.

Solution

RJH was retained by the USACE, Sacramento District to design enlargements to six of the earthen dikes.  RJH reviewed hundreds of documents to identify data gaps in the geotechnical information and developed a geotechnical field investigation program consisting of 62 borings, 23 test pits, in-situ water pressure testing, piezometer construction, and geophysical surveys.  Using this information, RJH worked with USACE and the Bureau of Reclamation (Reclamation) to develop preferred concepts for the dike raises.  For four of the raises, the preferred method was to install a reinforced concrete floodwall along the dike crest.  The preferred concept for the other two dikes consisted of raising the earthen embankments.

The project submittal included a 180-page drawing package, specifications, design report, and cost estimate.  Primary project components included embankments, floodwalls, culverts, roadways, utilities, and retaining walls.  RJH supported and participated in three, one-week-long quantitative risk assessments with USACE and Reclamation and participated in a value engineering workshop during design.  RJH also provided engineering services during bidding and construction for this $50 million project.