Why do some lakes have a concave surface before water falls over a weir?

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SUMMARY

The concave surface of lakes before water flows over a weir is primarily due to the principles of adhesion and surface tension. As deeper water molecules fall over the weir first, the surface layers attempt to maintain their original configuration, creating a concave shape. This phenomenon is similar to experiments measuring fluid surface tension, where surface layers exhibit a tendency to adhere to objects, such as a ring, submerged in water. The introduction of substances like detergent can temporarily disrupt this concave shape by altering surface tension.

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Why does the surface of some lakes become concave just before the water falls over a weir?
 
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Rothiemurchus said:
Why does the surface of some lakes become concave just before the water falls over a weir?

Two words : adhesion and surface tension... :wink:

The deeper watermolecules will fall over first, then the top layers of the water. the reason for this is that the surface will always try to maintain or restore the original configuration once some perturbation has occurred...
Think of what would happen if you would slowly move a ring out of water. the surface-layers will try to stick to the rings...they want the ring to stay in the water and thus maintain the original configuration. These things are used in experiments to measure the surface tension of fluids in general...

marlon
 
If I dropped some detergent on the surface the concave shape would disappear briefly?
 

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