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### Required Flow Velocity in Sewers Formula and Calculator

Civil Engineering and Design

Fluid Flow Hydraulic and Pneumatic Engineering and Design Menu

Required Flow Velocity in Sewers Formula and Calculator

To ensure full carriage of the solids, soils, refuse, and sand conveyed by storm and sanitary sewers, minimum flow velocities must be maintained. For storm sewers, the minimum flow velocity should be 3 ft/s; for sanitary sewers, 2 ft/s is recommended. Full-flow velocity of the liquid in a sewer is given by:

Formula 1,

*V = ( 0.59 / n ) · d ^{2/3} · S^{1/2} *

Where:

V = Flow velocity ft/s,

Q = Flow quantity, ft^{3} / s

n = coefficient dependent on roughness of conduit surface,

S = energy loss, ft/ft of conduit length; approximately the slope of the conduit invert for uniform flow,

d = inside diameter of pipe, ft.

The value of n can range from 0.013 in smooth concrete sewers to 0.02 in plain pipe. Further, n usually increases as a sewer pipe ages. Specific n values are given in engineering handbooks such as those cited in the references section of this webpage.

The water flow quantity, cu ft/s for a full-flowing sewer pipe is given by:

Formula 2,

Q = * ( 0.463 / n ) · ( d ^{8/3} · S^{1/2} ) *

Related:

- Flow Velocity in Straight Sewers Formula and Calculator
- Storm Drain Pipe Size Requirement Formula and Calculator
- Rainfall Runoff Rate Formulas and Calculator
- Pipe Roughness Coefficients Table Charts | Hazen-Williams Coefficient | Manning Factor
- Darci's Equation Fluids Flow Equation
- Head Loss Darcy - Weisback Equation
- Head Loss Darcy Calculator - Weisback Equation
- Fluid Flow Regimes Review
- Orifice Plate Flow Calculations and Design
- Pressure Drop Along Pipe Length - Fluid Flow Hydraulic and Pneumatic
- Function for open channel flow rate with input variable for inflow

References:

- Hicks - Handbook of Civil Engineering Calculations,
- McGraw-Hill.
- Kevin D. Wills, M.S.E., P.E., Consulting Engineer.