Canyon Lake Dam Reconstruction

Canyon Lake is the centerpiece of Canyon Lake Park in Rapid City, South Dakota.  The dam’s primary spillway has experienced chronic seepage, which caused concern over its stability and service life. 

The dam’s 200-foot-long spillway is constructed on fractured limestone on one end and alluvial soils on the other end. Ground penetrating radar, combined with concrete/bedrock core holes, revealed that underground cavities were allowing water to pass under the dam.  Cement grout was pressure injected to fill voids in the bedrock foundation and at the structure/bedrock interface, while a wall of steel sheet pile was driven deep into the soil foundation to complete the barrier.   Bedrock excavation, careful placement of sheet pile, and pressurized grout were used to seal the transition between the limestone and the sheet pile.  Waterstops at the joints between concrete sections completed the seepage barrier.  

Stanley Consultants evaluated the alternatives, and provided preliminary and final design for this $3.7 million dam reconstruction, which has a lifespan of over 50 years and is designed to safely pass a 500-year flood.