Effluent weirs of settling tanks should be level in order to prevent an uneven flow and

• A. Overflow
• B. Short circuiting
• C. Turbulence
• D. Backwashing

Answer: (B)

Uniform effluent distribution across the settling tank depends on a level weir so water exits evenly along the width. If the weir is not level, water will find the lowest path and rush toward the outlet through a preferential, low-resistance channel. That creates a short, direct flow from inlet to outlet, bypassing much of the settled sludge and drastically reducing detention time and solids removal. This is why short circuiting is the issue that level weirs prevent, making it the correct concept. Overflow would stem from capacity or level control problems, turbulence is a byproduct of flow irregularities but not the primary concern here, and backwashing is not part of settling tank effluent distribution.