Overflow Problems
Uneven or Excessive Weir Overflow
The outlet weirs must draw clarified water evenly. Unlevel, fouled or overloaded weirs create local high velocities that pull solids over.
Understanding the Problem
Weirs control how clarified water leaves the settling zone. If they are not level, most of the flow exits over the low section, concentrating upflow velocity there and dragging solids out.
Weir loading rate (flow per metre of weir) is a design check; exceeding it causes draw-down and carryover regardless of the plate area available.
Levelling, cleaning and, where needed, adding weir length or launders resolves most overflow problems.
Common Symptoms
- ›Water overflowing more on one side
- ›Localised solids carryover at weirs
- ›Weir loading above design
- ›Fouling or debris on weir plates
Causes & Corrective Actions
Cause
Unlevel weirs
Corrective Action
Re-level weir plates for uniform overflow.
Cause
Fouled / obstructed weirs
Corrective Action
Clean weirs and launders regularly.
Cause
Weir loading rate too high
Corrective Action
Add weir length / launders to spread the draw.
Cause
Hydraulic overload
Corrective Action
Cap flow at design; equalize peaks.
Prevention
Related Pages
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