Public Safety at Low-Head Dams

Low-head dams across the United States, from New Jersey to Oregon, continue to needlessly take lives as victims are lured into the seemingly placid water below the dams. Yet, the submerged hydraulic jumps and resulting reverse rollers can be readily analyzed, and various types of dam retrofits can provide cures. Low-head dams are often called “drowning machines.” The submerged hydraulic jump is an energy-dissipating underwater jet that can often maintain enough kinetic energy to cause it to travel downstream and then rise to the surface as a “boil,” with a portion of the water of the jet flowing back toward the dam. This represents the reverse roller. Hydraulic engineering analyses can define the approximate location of the boil and the likely velocity of the reverse flow. It is this reverse flow that carries a victim back to the base of the dam, where he or she is trapped in a vicious cycle. Six case studies of drowning are described, the related adverse hydraulics are presented, and suitable dam retrofits are outlined. Included in the case studies are a grade control structure (GCS) on the Salt River in the Phoenix area, a fish ladder in Oregon, a water supply structure on the Raritan River in New Jersey, a low-head dam owned by a water supply agency in West Virginia, a Clear Creek drop structures in Adams County, Colorado, and a U.S. Army Corps of Engineers (USACE) dam in Denver. Tragic loss of life at each of the structures could have been prevented had the design engineer and owner exercised a reasonable standard of care and had been familiar with the related published literature. 14 pp., 7 figures, 6 references.