# Flow in a swale

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Flow (Q) in an open channel, such as a swaleA 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., 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 swaleA 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. (m3/s)
• A = the cross sectional area of the swaleA 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. (m2)
• P = the wetted perimeter of the swaleA 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. (m)
• S = the longitudinal slope (m/m)
• n = Manning's coefficient (dimensionless)