Many members of the general public find themselves closer than ever to seemingly safe and suitable reservoirs and other waterways for recreational activities. As the population density of the United States continues to rise, previously remote waterways and hydraulic structures are now easy to access and are neighbors to residential communities. Reservoirs, waterways and other areas near dams are popular locations for recreational activities. Further, new hydraulic structures which change the character of the waterway may appear to create new opportunities for recreation.
With the growth in popularity of recreational activities and an increasing use of reservoirs associated with hydraulic structures, there has been a corresponding increase in the number of incidents and fatalities related to the use of these facilities. It is an unfortunate truth that unskilled, novice recreational users may not recognize the serious threat posed by some innocuous appearing hydraulic structures. While high dams and spillways present an imposing facade, low head and small diversion dams and weirs do not appear menacing. The placid, shallow water in areas surrounding such structures can lull the novice into a false sense of security. Short drops over low heads during high water can seem harmless, much like a waterside at an amusement park.
While the water downstream of a low head often appears harmless, the plunging water flow over the dam may result in turbulent, hazardous conditions which can be deadly. Under certain flow conditions, a “reverse flow” or “reverse roller” is created. These flow conditions carry objects back towards the face of the dam where they are subject to the water falling over the crest. Objects (or persons) are then submerged by the falling water only to resurface and recirculated towards the face of the dam by the “reverse roller.” The uniform nature of the current along the length of the structure makes escape or rescue difficult and sometimes impossible. (Chambers, 6/03)
The hidden, deadly hydraulic hazard of the “reverse roller” has claimed the lives of many paddle sport participants. Tragically, attempted rescues of trapped victims have also resulted in deaths among rescuers. While it is impossible to estimate the number of fatalities which have arisen from recreational activities near low head dams and other water control structures, statistics obtained from specific rivers support the significance of the public safety hazard. Twenty nine (29) people died on the Fox River in Illinois over a ten year period. As such, these structures have been described by some as “drowning machines.”