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Curb cuts

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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==
<div style="float: right">{{#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<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>
 
{{Plainlist|1=Where:
*''W<sub>T</sub>'' is the width of the inlet for complete capture (m),
*''Q'' is the design flow perpendicular to the inlet (m<sup>3</sup>/s)
*''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
*''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::
<math>R_c=1-\left ( 1-\frac{W}{W_T} \right )^{1.8}</math>
{{Plainlist|1=Where:*''R<sub>c</sub>'' is the proportion of flow entering the curb cut, and *''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==
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 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</mamath>
==Curb cuts Gallery==48% of the 0.08 m<sup>3<gallery mode="packed" widths=300px heights=300px/sup>LSRCA curb/s (i.jpg| Curb cut used as a controlled overflow route from permeable paving to a bioretention facility with monitoring well, Lake Simcoe Region Conservation Authority, Newmarket, ONCurb cut CNTe.jpg| Curb cut into a bioretention facility in Hinsdale, IL0. 038 m<sup>3<br/sup>Decorative aggregate in the center of the facility reduces erosion and dissipates power inflow around the inlet area. A monitoring/maintenance well can be seen in s) would enter the foreground. <br>[[Acknowledgements| Photo credit: CNT]]Curb cut AV.jpg | Curb cut into a bioretention facility in Brown Deer, WI. <br>Aggregate is used to reduce erosion around cell through the inlet areaas designed. <br>[[Acknowledgements| Photo credit: Aaron Volkening]]</gallery>
==Curb cuts gallery=={{:Curb cuts: Gallery}}----[[category: modelingCalculations]]