Hole (River)

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Holes, often referred to as "souse-holes", or "stoppers", are formed when water pours over the top of a submerged object, causing the water downstream to flow back over the top of the water which rushes over the submerged object. Holes can be particularly dangerous: a boater may become stuck in the recirculating water. In high volume water, holes will dramatically aerate the water, possibly to the point where it may even lose the capacity to carry any water crafts.

Some of the most dangerous types of holes are formed by lowhead dams (weirs), underwater ledges, and similar types of obstruction. In lowhead dams, the hole has a very symmetrical character - there's no weak point - and where the sides of the hydraulic are often blocked by a man-made wall, making it impossible to slip off the side of the hydraulic. Lowhead dams are insidiously dangerous because their danger cannot be easily recognized by people who have not studied whitewater.