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

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The concave surface of some lakes before water flows over a weir is primarily due to adhesion and surface tension. As deeper water molecules move over the edge first, the surface layers attempt to maintain their original configuration, creating a concave shape. This phenomenon is similar to how surface layers of water cling to objects, like a ring, when removed from the water. Adding detergent disrupts surface tension, causing the concave shape to temporarily disappear. Understanding these principles can help explain fluid behavior in various contexts.
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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 occured...
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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