LOWHEAD DAMS
Low-head dams (manmade concrete structures) typically span the entire width
of a river and should be avoided in most cases and be approached very carefully.
With strong current flowing over a lowhead, they are potential drowning
machines. Once caught in the downstream-side hydraulic, it is nearly impossible
to get out.
- The downstream side of a dam is the most dangerous as this is where the
hydraulic is created.
- Boats trapped against the downstream side quickly fill with water and
capsize, throwing occupants into the dangerous waters.
- When caught in the hydraulics of a low-head dam, you are carried to the
face of the dam, where the water pouring over it will wash down under to a
point downstream called the boil.
- The boil is a position where the water below surfaces and moves either
downstream or back toward the dam. A person caught in a boil dam may
surface, only to be caught in the backwash again and carried to the face of
the dam, continuing the cycle. Even with a PFD on, the hydraulic may
continue to pull a person under. The tremendous force may pull off a PFD
from a struggling person.
- Dams do not need to have a deep drop to create a dangerous backwash.
During periods of high water, the backwash current problems get worse, and
the length of the backwash current is extended downstream.
Although low-head dams do not always look dangerous, they can create a
life-threatening situation. You should always know the local area, follow
warning signs, markers or buoys, and keep well clear of low-head dams.
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