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| + | ==Overview== |
| <poem> | | <poem> |
− | Curb cuts are a form of LID/BMP [[Inlets|inlet]]. | + | 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? | + | 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. |
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| As this inlet width is directly proportional to longitudinal slope; the required curb cut width increases rapidly on steeper roads. | | 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.''' | + | '''Standard width (450 mm), as included in Ontario Provincial Standard Drawings (OPSDs) should be compared to and modified for the flow requirements of the practice.''' |
| </poem> | | </poem> |
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| {| class="wikitable" | | {| class="wikitable" |
− | |+The OPSD collection of standard drawings for curb cuts include | + | |+The Ontario Provincial Standard Drawing (OPSD) collection for curb cuts |
| |- | | |- |
| !Flow direction | | !Flow direction |
− | !From asphalt catchment | + | !From asphalt curb and gutter |
− | !From concrete catchment | + | !From concrete curb and gutter |
| + | !From either asphalt or concrete outlet |
| |- | | |- |
− | |30 - 45 deg | + | |30 to 45 degree |
| |605.020 <ref name =OPSD>http://www.roadauthority.com/Standards/?id=b00e3771-6095-4257-b029-1d9879418039</ref> | | |605.020 <ref name =OPSD>http://www.roadauthority.com/Standards/?id=b00e3771-6095-4257-b029-1d9879418039</ref> |
| |605.010 <ref name =OPSD/> | | |605.010 <ref name =OPSD/> |
| + | |605.040 Asphalt Spillways <ref name =OPSD/> |
| |- | | |- |
− | |90 deg | + | |90 degree |
| |604.020 <ref name =OPSD/> | | |604.020 <ref name =OPSD/> |
| |604.010 <ref name =OPSD/> | | |604.010 <ref name =OPSD/> |
| + | |605.040 Asphalt Spillways <ref name =OPSD/> |
| |} | | |} |
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| ==Sizing== | | ==Sizing== |
− | <div style="float: right">
| + | 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>: |
− | {{#widget:WolframAlpha|id=664012476f5d9635d57cd58920e763e6}}</div>
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− | To completely capture linear flow travelling along a gutter perpendicular to a curb inlet, the inlet must be of width<ref>Chin, D.A. (2012), Water-Resources Engineering (3rd Edition), ISBN-13: 978-0132833219</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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| {{Plainlist|1=Where: | | {{Plainlist|1=Where: |
− | *''W<sub>T</sub>'' is the width of the inlet for complete capture (m), | + | *''W<sub>T</sub>'' is the total width of inlet for complete capture (m), |
| *''Q'' is the design flow perpendicular to the inlet (m<sup>3</sup>/s) | | *''Q'' is the design flow perpendicular to the inlet (m<sup>3</sup>/s) |
| *''S<sub>0</sub>'' is the longitudinal slope ratio | | *''S<sub>0</sub>'' is the longitudinal slope ratio |
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| *''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)}} |
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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:: | + | The value obtained for total inlet width (''W<sub>T</sub>'') can then be divided by the chosen number of inlets to determine the required width of each individual curb cut inlet. Curb cut inlets draining roadways should be a minimum of 0.45 m in width and are typically no wider than 1.5 m. The chosen number of inlets may be adjusted up or down to ensure individual inlet widths are within this range. |
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| + | Where the available space for curb cuts is constrained and a greater flow into the BMP is desired, the effective cross slope (''S<sub>x</sub>'') may be increased by adding a depressed concrete apron. |
| + | |
| + | Where the intention is to capture only a portion of flow from the design storm event, the proportion of flow entering the curb inlet under such conditions 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)}} |
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− | 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.
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| ==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 1 in 25 year design storm produces a peak flow of 0.08 m<sup>3</sup>/s.
| + | Three (3) curb cut inlets of 1 m width each, representing a total curb cut width of 3 m, are proposed 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 cross slope ratio 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 from the road drainage area. |
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− | The width of inlet to capture 100% of this flow is:: | + | The total width of curb cut inlets required 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> |
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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 peak flow conditions during the design storm event 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> |
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− | 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. | + | So only 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 inlets as designed. |
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| ==Curb cuts gallery== | | ==Curb cuts gallery== |
| {{:Curb cuts: Gallery}} | | {{:Curb cuts: Gallery}} |
| ---- | | ---- |
− | [[category: modeling]] | + | [[category: Calculations]] |
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| + | ==References== |