What is the purpose of an overflow weir in a basin?

• A. To maintain a consistent surface level and prevent spillover into basins during high flows.
• B. To generate electricity.
• C. To aerate water.
• D. To measure turbidity.

Answer: (A)

The main idea is controlling how high the water climbs in a basin so flow stays predictable. An overflow weir sets a defined crest at which water can spill over. When inflow is moderate, water stays below the crest; as inflow increases and reaches that crest, water spills over in a controlled way, keeping the basin surface at a steady level. This prevents random, uncontrolled spillover into downstream basins, reduces surge effects and potential damage, and helps ensure a consistent flow to downstream processes. It’s not used for electricity generation, which would require turbines; it doesn’t aerate water, which needs air diffusers or other equipment; and it isn’t a device for measuring turbidity, which relies on sensors or sampling.