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
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