DISCHARGE & CRITICAL DEPTH

Critical depth from Q²·T = g·A³ (Fr = 1). Manning only used if “Q from h”. SI (m·s)

Input parameters

Units

Affects inputs/outputs

Q source

Needed for h_c

Channel type

Manning’s n (—; if Q from h)

Channel slope S (–)

Used if Q from h

Bottom width (b, m)

Flow depth (for Q-from-h) (h, m)

Discharge (Q) (m³/s)

Side slope (z:1)

For trapezoidal/triangular

Discharge

Discharge used (Q)

—

m³/s

Critical depth

Critical depth (h_c)

—

Critical area (A_c)

—

m²

Critical wetted perimeter (P_c)

—

Critical hydraulic radius (R_c)

—

Critical top width (T_c)

—

Critical velocity (V_c=Q/A_c)

—

m/s

Critical slope (S_c)

—

–

Froude at critical (Fr_c)

—

–

Critical depth satisfies Q²·T = g·A³. For triangular set b=0 and use side slope z.