Flow rate over weirs — rectangular sharp-crested, V-notch (triangular), and broad-crested. Solve for Q (from head H) or find the required head H for a target flow rate. Includes approach velocity correction.
Open Channel Flow · HydraulicsWeir type:
Solve for:
Weir discharge equations:
Approach velocity correction:
Typical discharge coefficient Cd values:
| Weir type | Cd | Notes |
|---|---|---|
| Rectangular sharp-crested | 0.61–0.65 | 0.62 standard, varies with H/P |
| V-notch 90° | 0.59–0.62 | 0.61 standard (Kindsvater-Shen) |
| V-notch 60° | 0.60–0.62 | Slightly higher than 90° |
| Broad-crested (smooth entry) | 0.85–0.90 | Approaches 0.848 theoretical |
| Broad-crested (sharp entry) | 0.75–0.82 | Entry losses reduce coefficient |
Head measurement:
H is always measured from the weir crest (top edge), not the channel bed. The gauge should be placed upstream at a distance of 3–4 times the maximum expected head to avoid drawdown effects near the weir face.