Question: What happens as the water level goes up towards
the dangerous level on the face of a dam?
Finding: Water begins to flow in the top tube when the water
level gets to the top of the bend in it. The water flows through
the tube until the reservoir water level has lowered to the
level of the bottom of the tube.
Reason: The tube acts as a siphon. The rising water level
has primed the siphon and it begins to siphon water from the
reservoir over the dam when the water level reaches the top
curve in the siphon. The siphon continues to move water over
the dam until the reservoir water level lowers to the level
of the open left end of the siphon tube. This is a self-priming
siphon. Most siphons require that the tube first be filled
with water by a person's actions. This one does not. It starts
even when there are no people around. It acts as an emergency
device to help reduce the water level in a reservoir when
it becomes tool high. Water spilling over the top of the dam
can cause it to fail and break allowing all the stored water
to flood down the stream below the dam.
