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| | <poem> |
| | Curb cuts are a form of LID/BMP [[Inlets|inlet]]. They include a variety of modified curbs and spillways. |
| | 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 |
| | !From either asphalt or 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/> |
| | |605.040 Asphalt Spillways <ref name =OPSD/> |
| | |- |
| | |90 deg |
| | |604.020 <ref name =OPSD/> |
| | |604.010 <ref name =OPSD/> |
| | |605.040 Asphalt Spillways <ref name =OPSD/> |
| | |} |
| | |
| | |
| ==Sizing== | | ==Sizing== |
| 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> |
| | |
| | {{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)}} |
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| 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> |
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| | |
| | {{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== | | ==Example== |
| A curb cut of 3 m is proposed as an inlet for an offline 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. |
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| 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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| 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, \or\ 48\ %</math> | | <math>R_c=1-\left ( 1-\frac{3}{9.71} \right )^{1.8}= 0.48</math> |
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| ==Curb cuts Gallery==
| | 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. |
| <gallery mode="packed" widths=300px heights=300px> | |
| LSRCA curb.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, ON
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| Curb cut CNT.jpg| Curb cut into a bioretention facility in Hinsdale, IL. <br>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 the foreground. <br>[[Acknowledgements| Photo credit: CNT]]
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| Curb cut AV.jpg | Curb cut into a bioretention facility in Brown Deer, WI. <br>Aggregate is used to reduce erosion around the inlet area. <br>[[Acknowledgements| Photo credit: Aaron Volkening]]
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| </gallery>
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| [[category: modeling]] | | ==Curb cuts gallery== |
| | {{:Curb cuts: Gallery}} |
| | ---- |
| | [[category: Calculations]] |