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==Sizing==
==Sizing==
To completely capture linear flow travelling along a gutter perpendicular to a curb inlet, the inlet must be of width<ref>U.S. Department of Transportation, Federal Highways Administration. 2013. “URBAN DRAINAGE DESIGN MANUAL.” https://www.fhwa.dot.gov/engineering/hydraulics/pubs/10009/10009.pdf.[[File:USFHWA 2009.pdf|view here]]</ref>::
To completely capture linear flow travelling along a gutter perpendicular to a curb inlet, the inlet must be of width<ref>U.S. Department of Transportation, Federal Highways Administration. 2013. “URBAN DRAINAGE DESIGN MANUAL.” https://www.fhwa.dot.gov/engineering/hydraulics/pubs/10009/10009.pdf.[[File:USFHWA 2009.pdf|view here]]</ref>:
<math>W_T=0.817Q^{0.42}S_{0}^{0.3}\left (\frac{1}{nS_{x}}\right)^{0.6}</math>
<math>W_T=0.817Q^{0.42}S_{0}^{0.3}\left (\frac{1}{nS_{x}}\right)^{0.6}</math>
*''S<sub>x</sub>'' is the cross slope ratio (typically between 0.015 and 0.04)}}
*''S<sub>x</sub>'' is the cross slope ratio (typically between 0.015 and 0.04)}}
Where the intention is to capture only a proportion of the flow, the ratio of flow entering the curb inlet may be calculated::
Where the intention is to capture only a proportion of the flow, the ratio of flow entering the curb inlet may be calculated:
<math>R_c=1-\left ( 1-\frac{W}{W_T} \right )^{1.8}</math>
<math>R_c=1-\left ( 1-\frac{W}{W_T} \right )^{1.8}</math>
A curb cut of 3 m is proposed as an inlet for an offline [[Bioretention|bioretention cell]] receiving runoff from an adjacent roadway. The gutter and the curb are made from smooth concrete with Manning's 'n' = 0.013. The x-slope is 3% and the longitudinal slope of the road is 2%. The 1 in 25 year design storm produces a peak flow of 0.08 m<sup>3</sup>/s.
A curb cut of 3 m is proposed as an inlet for an offline [[Bioretention|bioretention cell]] receiving runoff from an adjacent roadway. The gutter and the curb are made from smooth concrete with Manning's 'n' = 0.013. The x-slope is 3% and the longitudinal slope of the road is 2%. The 1 in 25 year design storm produces a peak flow of 0.08 m<sup>3</sup>/s.
The width of inlet to capture 100% of this flow is::
The width of inlet to capture 100% of this flow is:
<math>W_T=0.817\times(0.08)^{0.42}\times(0.02)^{0.3}\left (\frac{1}{0.013\times0.03}\right)^{0.6}=9.71\ m</math>
<math>W_T=0.817\times(0.08)^{0.42}\times(0.02)^{0.3}\left (\frac{1}{0.013\times0.03}\right)^{0.6}=9.71\ m</math>
The proportion of water entering the bioretention cell under these flow conditions would be::
The proportion of water entering the bioretention cell under these flow conditions would be:
<math>R_c=1-\left ( 1-\frac{3}{9.71} \right )^{1.8}= 0.48</math>
<math>R_c=1-\left ( 1-\frac{3}{9.71} \right )^{1.8}= 0.48</math>