Flow in a swale

Flow (Q) in an open channel, such as a swale, may be calculated using Manning's equation: $Q=VA={\frac {R^{\frac {2}{3}}S^{\frac {1}{2}}}{n}}$ Where: $R={\frac {A}{P}}$

Where:

• Q = the flow in the swale (m³/s)
• A = the cross sectional area of the swale (m²)
• P = the wetted perimeter of the swale (m)
• S = the longitudinal slope (m/m)
• n = Manning's coefficient (dimensionless)

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.