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| + | |
| + | ==Overview== |
| + | <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 Ontario Provincial Standard Drawings (OPSDs) should be compared to and modified for the flow requirements of the practice.''' |
| + | </poem> |
| + | |
| + | {| class="wikitable" |
| + | |+The Ontario Provincial Standard Drawing (OPSD) collection for curb cuts |
| + | |- |
| + | !Flow direction |
| + | !From asphalt curb and gutter |
| + | !From concrete curb and gutter |
| + | !From either asphalt or concrete outlet |
| + | |- |
| + | |30 to 45 degree |
| + | |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 degree |
| + | |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> |
| | | |
− | Where the intention is to capture only a proportion of the flow, the ratio of flow entering the curb inlet may be calculated:: | + | {{Plainlist|1=Where: |
| + | *''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) |
| + | *''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)}} |
| + | |
| + | 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. |
| + | |
| + | 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> |
− |
| + | |
| + | {{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)}} |
| + | |
| ==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.
| + | 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. |
| | | |
− | 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> |
| | | |
− | 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, \or\ 48\ %</math> | + | <math>R_c=1-\left ( 1-\frac{3}{9.71} \right )^{1.8}= 0.48</math> |
| + | |
| + | 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. |
| | | |
− | ==Curb cuts Gallery== | + | ==Curb cuts gallery== |
− | <gallery mode="packed" widths=300px heights=300px>
| + | {{:Curb cuts: Gallery}} |
− | 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
| + | ---- |
− | 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]]
| + | [[category: Calculations]] |
− | 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]]
| |
− | </gallery>
| |
| | | |
− | [[category: modeling]]
| + | ==References== |