Drowning Machines: Low Head Dam Hydraulics and Hazard Remediation Options Anita Rogacs, Cole Marr, Anizka Garcia Rose-Hulman Institute of Technology, Terre Haute, Indiana Introduction A father and two sons set out for a day of excitement as they head off to Licking River, Kentucky. Chad, the youngest, has never been kayaking and this is his big chance to ‘learn the ropes’. With life jackets fastened, all three embark on their quest for fun as they start into the water. Slipping through the waves, there are bright smiles on their faces and excitement in their eyes, when the father, Larry Ratliff, catches sight of a menacing horizon up ahead. He recognizes the danger and looks for his sons. Chad is too far away to be warned and as his father watches in horror, his youngest son drops out of sight. In a panic Larry paddles over the low-head dam after his son, thinking that somehow he will save Chad. Larry is immediately pulled into the hydraulic as well. Both father and son struggle, but ultimately lose their battle. Both are pronounced dead at the scene. (“Kentucky”) Many more tragic stories just like the one related above happen every year, and have been occurring since the creation of low-head dams. A low head dam is a water control structure usually below 10 feet high, (Elverum, 2003) and has several uses. These uses include: ensuring a constant water supply in low flow conditions (White River, 2005), grade control, aesthetics, and protection for utility crossings. They also have recreational uses; they provide pools of water in the river for fishing and boating, and are jumps that canoeists and kayakers paddle over for a thrill. (Low Dams) Figure 1: Rafters at low-head dam History Powering mills was one of the main reasons for the development of the low-head dam. Water wheels were used to power mills in the 19th century, and these wheels required a constant supply of water. Low head dams fulfilled this need because they enable the storage of water for use in low flow conditions. (Colley) Figure 2: Mabry Mill, Virginia Figure 3: Reed Springs Mill, Missouri Low-head dams also came into use as early settlers became concerned with the storage of irrigation water. Originally local water supplies held enough water for their limited needs. Unfortunately, this dependence on natural water resources forced them to cope with the varying seasonal discharge. During the late 1880’s and early 1890’s a few dams were built, but they were “make-shift affairs,” in some cases beaver dams were upgraded. Orcharding accelerated technological growth due to the increased need for more elaborate irrigation works and an increased need for storage of water. In the early 1900’s dams of varying sizes and qualities were built, including earth dams. Earth dams were common because of the availability of construction materials, and their relatively low cost. (“Irrigation Technology”) Types of Dams Dams consist of timber, rock, earth, masonry, concrete, or a combination of the afore mentioned materials. (dam, 2005) There are six basic types of dams. These are: 1) Concrete Gravity Dams, 2) Concrete Arch Dams, 3) Concrete Buttress Dams, 4) Earth Dams, 5) Earth and Rock Fill Dams, and 6) Concrete Faced Rock Fill Dams. Concrete Gravity Dams rely on their own weight to withstand the applied forces. Concrete Arch Dams and Buttress Dams require less concrete and are consequently cheaper to build, they are designed to transfer some of their applied forces to the foundation that supports them. Earth Dams are consist completely of homogenous, impermeable earth material. Earth and Rock Fill Dams have an impermeable earth or clay core, covered with a permeable rock fill outer layer. Concrete Faced Rock Fill dams mainly consist of permeable rock fill, which is then covered on the upstream face with an impermeable concrete slab. (Woodward, “Types” 2004) Figure 4: Concrete Gravity Dam Figure 5: Concrete Arch Dam Figure 6: Concrete Buttress Dam Figure 7: Earth Dam Figure 8: Earth and Rock Fill Dam Figure 9: Concrete Faced Rock Fill Dam Cost The cost of construction varies widely due to the many variables involved in an estimate. The type of dam influences the amount of manpower needed and the type of construction materials required. (“Concrete”) In the case of an Earth and Rock Fill Dam or a Concrete Faced Rock Fill Dam, many times the most economical way to obtain the large volume of rock needed is to use the rock that needs to be excavated during the building of the spillway. This may not be possible if the quality of the rock acquired from the spillway is not acceptable for construction. Another important variable to take into account is the distance that the construction materials must be hauled to get them to the work site. (Woodward, “Construction” 2004) If, for example, we looked at a 15 ft. wide by 5’ tall dam, with a road into the site, with no materials at the site (all material and equipment has to be brought in), and about 20 miles from the materials, the price for the dam construction might be around $50,000. If one was to try to use this same dam as a power source, the construction including a power house and all the extra equipment, could cost around $300,000-$500,000. Or, if one were to consider a bigger dam, one 200 ft. wide and 15 ft. high, also with access to a road, and material or equipment on site, and about 70 miles from the materials, the construction cost could amount to 1-2 million dollars. (Desrochers, 2005) Safety Low-head dams are found throughout the United States and pose a considerable safety risk to the general public. The safety risk arises from the fact that the structures often look harmless or even inviting to the recreational water user. The danger of these overflow structures is that the downstream side of a low-head dam contains a submerged hydraulic jump or “hydraulic” as it is referred to in the boating community (Tschantz, 2003). The hydraulic jump creates a recirculating current which can trap water-goers in a seemingly endless cycle of being pulled under, struggling back to the surface, being pushed back toward the falling water, and once again being pushed under (Elverum & Smalley, 2003). These low-head dams put an unsuspecting public in danger time and time again. Figure 10: Roller Effect The exact number of low-head dam structures throughout the United States is somewhat vague. Some states do keep track of these structures, but even in these cases the numbers can be inaccurate. Pennsylvania maintains a list of 280 low-head structures and Virginia estimates between 50 and 100 in their state (Tschantz, 2003). Some confusion also arises from the fact that there are no universal definitions or dimensions available to define a “low-head” dam. According to Leutheusser and Birk (1991), in order to “drownproof” one of these structures the weir height would have to be increased to approximately seven times the original height. The fact that there have been no easy or inexpensive retrofits developed for these structures means that year after year low-head dams are claiming lives throughout the world. While Larry Ratliff, mentioned previously, recognized the danger of low-head dams and would not have willingly gone over the structure if not for his son, this is exactly what many people do. Many times canoeists and kayakers along with other pleasure-seeking riders, willingly ride over these dams. A typical example of this is an event in Minnesota described by Elverum and Smalley (2003) in a brochure for the Minnesota Department of Natural Resources titled “The Drowning Machine.” In July 1979, a 25-year-old man on an air mattress went over the Berning’s Mill Dam, apparently on a dare. He was caught in the recirculating current and began a cycle of being pulled down and trapped against the dam. Two canoes attempted to help, both of which were pulled into and trapped in the recirculating current of the dam. A state trooper and several bystanders attempted a rescue, but were unsuccessful. In the end three people died in an event that is all too typical at low-head dams. The structure appeared harmless in the beginning, as most do, and in the end kept its reputation as one of the most dangerous aspects of our nation’s waterways. Project Description The Indiana Department of Natural Resources (IDNR) Engineering and Dam Safety Group and the IDNR Division of Law Enforcement appointed our research group to conduct an intensive investigation on low head dam hydraulics and affordable hazard remediation alternatives. Since the hazards of low head dams have been recognized, over the last few decades, various attempts have been made to eliminate the dangerous hydraulics at these structures. However, some proving to be more effective than others. Due to IDNR’s wide range of needs, testing will be performed on a characteristic lowhead dam. The goal in modeling these dams is to arrive at a suitable remediation alternative for the majority of low-head dams in the state by designing a retrofit that reduces the dangerous hydraulics or by improving an already existing design. The current options may serve as a useful starting point for improved hazard remediation options. Along with the reduction of dangerous hydraulic features, we are also concerned with the environmental impact and implementation cost of any remediation option which may be available. Despite the fact that our retrofit design will be applicable to similar low-head dams, only those that have the same design as the model tested can be expected to follow the experimental results. The standards for classification of low-head dams, fatality statistics, final retrofit solution, and guidelines for implementation will be provided to IDNR in the final report. Project Approach To carry out our project successfully, we will first conduct an intensive literature search on low head dam structures, hazards and fatality statistics. After obtaining necessary background information, a characteristic low head dam will be chosen for experimentation. The phenomenon will be tested by numerical modeling using Flow3D (Flow Science Inc.), a fluids modeling software that utilizes finite element analysis. Both quantitative and qualitative testing will be conducted on the velocities and flow direction of the recirculating and eddy currents using different flow rates. A physical model will then be built to verify the accuracy of the numerical model. Furthermore, successful simulation of a retrofit that results in a significant reduction of the dangerous hydraulics will be tested on the physical models as well. For the physical modeling we will observe the characteristics of both the recirculating and eddy current. Using objects of varying size and material we will also assess the reaction of a human body that comes in contact with the recirculating current. The data from the analytical and physical models will be compared, and if they do not agree we will revise the computer model to be in line with the physical model. The agreeing models will be re-tested and the final data compiled. References Elverum, Kim A. and Tim Smalley. (2003). The Drowning Machine. Retrieved on June 10, 2005, from the Boat and Water Safety Section Minnesota Department of Natural Resources <http://files.dnr.state.mn.us/education_safety/safety/boatwater/ drowningmachine.pdf >. Leutheusser, Hans J., and Warren M. Birk. Drownproofing of Low Overflow Structures. Journal of Hydraulic Engineering. February, 1991. Vol.117, No.2. Tschantz, Bruce A. Public Hazards at Low-head Dams: Can We Make Them Safer? National Dam Safety Conference Proceedings, 2003 Dam Safety Conference, Minneapolis, September 2003. “Kentucky.” American Whitewater. Accessed 20 June 2005 <www.americanwhitewater.org/safety/archive/year/1997/>. Elverum, Kim, and Tim Smalley. “The Drowning Machine.” Boat and Water Safety Section. Minnesota Department of Natural Resources, 2003. White River Citizen’s Advisory Council Meeting. Indianapolis DPW Engineering Office. Meeting Summary, 12 Jan. 2005 <www.in.gov/idem/mycommunity/wrac/meetsums/jan_12_05.html>. “Low Dams.” Miami Conservancy District. 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