Curb gutter Flow Width formula |
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\( q \;=\; \left( \dfrac{ Q \cdot n }{ 0.56 \cdot m_c^{5/3} \cdot m_l^{1/2} } \right)^{3/8} \) (Curb Gutter Flow Width) \( Q \;=\; \dfrac{ 0.56 }{ n } \cdot m_c^{5/3} \cdot m_l^{1/2} \cdot q^{8/3} \) \( n \;=\; \dfrac{ 0.56 }{ Q } \cdot m_c^{5/3} \cdot m_l^{1/2} \cdot q^{8/3} \) \( m_c \;=\; \left( \dfrac{ Q \cdot n }{ 0.56 \cdot m_l^{1/2} \cdot q^{8/3} } \right)^{3/5}\) \( m_l \;=\; \left( \dfrac{ Q \cdot n }{ 0.56 \cdot m_c^{5/3} \cdot q^{8/3} } \right)^2\) |
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| Symbol | English | Metric |
| \( q \) = Flow Width | \(ft\) | - |
| \( Q \) = Gutter Flow Rate | \(ft^3 \;/\; sec\) | - |
| \( n \) = Manning's Roughness Coefficient | \(dimensionless\) | - |
| \( m_c \) = Roadway Cross Slope | \(dimensionless\) | - |
| \( m_l \) = Longitudinal Slope of Pavement | \(dimensionless\) | - |
Curb gutter flow width, also called gutter spread, is the lateral extent of water flowing in the gutter along the edge of a roadway. It's the measure of how far the water spreads from the curb into the street or shoulder. This width is used in the design of stormwater drainage systems because it directly impacts traffic safety and the capacity of the gutter to intercept and convey runoff. Factors such as the amount of runoff, the longitudinal slope of the gutter, the cross slope of the pavement, and the roughness of the gutter surface all influence the resulting flow width. Engineers calculate and consider the curb gutter flow width to ensure that during design storm events, the water does not spread excessively into travel lanes, thereby maintaining safe driving conditions and preventing flooding.
