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| + | <poem> |
| + | Curb cuts are a form of LID/BMP [[Inlets|inlet]]. |
| + | They are well suited to retrofit scenarios and to collect runoff from catchments with relatively gentle longitudinal slope, and/or a greater cross slope. This might be the local topography of a parking lot or a piece of parkland? |
| + | As this inlet width is directly proportional to longitudinal slope; the required curb cut width increases rapidly on steeper roads. |
| + | '''Standard width (450 mm), as included in OPSD drawings should be compared to and modified for the flow requirements of the practice.''' |
| + | </poem> |
| + | |
| + | {| class="wikitable" |
| + | |+The OPSD collection of standard drawings for curb cuts include |
| + | |- |
| + | !Flow direction |
| + | !From asphalt catchment |
| + | !From concrete catchment |
| + | |- |
| + | |30 - 45 deg |
| + | |605.020 <ref name =OPSD>http://www.roadauthority.com/Standards/?id=b00e3771-6095-4257-b029-1d9879418039</ref> |
| + | |605.010 <ref name =OPSD/> |
| + | |- |
| + | |90 deg |
| + | |604.020 <ref name =OPSD/> |
| + | |604.010 <ref name =OPSD/> |
| + | |} |
| + | |
| ==Sizing== | | ==Sizing== |
| <div style="float: right"> | | <div style="float: right"> |
| {{#widget:WolframAlpha|id=664012476f5d9635d57cd58920e763e6}}</div> | | {{#widget:WolframAlpha|id=664012476f5d9635d57cd58920e763e6}}</div> |
− | | + | |
− | To completely capture linear flow travelling along a gutter perpendicular to a curb inlet, the inlet must be of width:: | + | 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> |
| | | |
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| *''S<sub>0</sub>'' is the longitudinal slope ratio | | *''S<sub>0</sub>'' is the longitudinal slope ratio |
| *''n'' is Manning's 'n' (between 0.012 and 0.016 for concrete, depending on surface treatment), and | | *''n'' is Manning's 'n' (between 0.012 and 0.016 for concrete, depending on surface treatment), and |
− | *''S<sub>x</sub>'' is the cross slope ratio}} | + | *''S<sub>x</sub>'' is the cross slope ratio (typically between 0.015 and 0.04)}} |
| | | |
− | Where the inlet width is constrained or 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> |
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| *''R<sub>c</sub>'' is the proportion of flow entering the curb cut, and | | *''R<sub>c</sub>'' is the proportion of flow entering the curb cut, and |
| *''W'' is the available curb cut width (m)}} | | *''W'' is the available curb cut width (m)}} |
| + | |
| + | Where the curb cut width is constrained and a greater flow into the BMP is desired, the effective cross slope may be increased by adding a depressed apron. |
| | | |
| ==Example== | | ==Example== |
− | 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 design storm produces 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:: |
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| <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> |
| | | |
− | 48% of the 0.08 m<sup>3</sup>/s flow would enter the bioretenteion cell through the inlet as designed. | + | 48% of the 0.08 m<sup>3</sup>/s (i.e. 0.038 m<sup>3</sup>/s) would enter the bioretention cell through the inlet as designed. |
| | | |
| ==Curb cuts gallery== | | ==Curb cuts gallery== |
| {{:Curb cuts: Gallery}} | | {{:Curb cuts: Gallery}} |
− | | + | ---- |
− | [[category: modeling]] | + | [[category: Calculations]] |