Case Study on Rosebud Dam Rehabilitation - Rosebud Sioux Reservation, South Dakota

Rosebud Dam is assumed to be a homogeneous earthfill structure with a crest length of 380 feet and a hydraulic height of 21 feet. The dam is located at the confluence of the east branch and west branch of Rosebud Creek in Todd County, at the southeastern edge of the town of Rosebud, South Dakota. The dam was constructed by the the Civilian Conservation Corps (CCC) and completed in 1935. It is owned by the Rosebud Sioux Tribe and was constructed to provide recreation and irrigation benefits to the tribal members. The SEED report prepare by BOR in 1988 indicated a poor hazard rating for Rosebud Dam. The hazard is posed to about one hundred human lives living on the flood plain within two miles downstream from the dam. The Tribe completed the DVA of the Rosebud Dam with assistance from the BOR. The flood routing indicated that 2.5 percent of the PMF, would result in overtopping of the dam. The final design comprised construction of roller compacted concrete (RCC) overtopping protection on the crest, downstream face of the existing dam, the left abutment and upstream dam face to provide scouring protection. In the initial construction phase, as soon as the vegetation was removed from the downstream face and toe of the dam, the seepage through the dam became intense, so much so that the Tribe decided to empty the reservoir in order to release the pressure of the seepages and a possible collapse of the dam. This action was taken on an emergency basis and rapidly completed. The seepage was reduced but not totally stopped. A well point system was installed to take care of the seepage and yet it was continuing. It is our view that the elevation difference between the seepage daylight points and the water table of the Ogallala Aquifer indicates a groundwater flow direction towards the seepage daylight points. Hence, much of the seepage water even after the installation of the well point system and emptying of the reservoir may have been coming from groundwater. Water Quality data derived by analysis of water samples from the seepage points and the lake indicated high distinction and probable ground water and surface water source respectively. The rehabilitation of the dam included a replacement of the sluice gate, relocation of the water line from the dam and rehabilitation of the outlet works. 7 pp.