Culvert outlet control headwater calculator

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Worked example — results

• ✓ HW ≤ allowable

Method, formulas and assumptions

• Area = 1.8*1.2 = 2.16 m²
• Hydraulic radius = 2.16/(2*(1.8+1.2)) = 0.36 m
• Velocity = 4/2.16 = 1.8519 m/s
• Losses (1 + ke + 2g n² L/R^(4/3)) V²/2g = (1+0.5+2*9.81*0.013^2*25/0.36^(4/3))*1.8519^2/(2*9.81) = 0.31876 m
• ho = max(TW, (dc + D)/2) = MAX(0.9,((4/1.8)^2/9.81)^(1/3)/2+1.2/2) = 0.99775 m
• HW = H + ho − L S = 0.31876+0.99775-25*0.005 = 1.1915 m

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