Difference between revisions of "Curb cuts"
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{{Plainlist|1=Where: | {{Plainlist|1=Where: | ||
| − | *''W<sub>T</sub>'' is the width of the inlet | + | *''W<sub>T</sub>'' is the width of the inlet for complete capture (m), |
| − | *''Q'' is the flow perpendicular to the inlet | + | *''Q'' is the design flow perpendicular to the inlet (m<sup>3</sup>/s) |
| − | *''S<sub>0</sub>'' is the longitudinal slope | + | *''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), | + | *''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}} | + | *''S<sub>x</sub>'' is the cross slope ratio}} |
| − | 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 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:: |
<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|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 design storm produces flow of 0.08 m<sup>3</sup>/s. | ||
Revision as of 18:09, 31 October 2017
Sizing[edit]
To completely capture linear flow travelling along a gutter perpendicular to a curb inlet, the inlet must be of width:: Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle W_T=0.817Q^{0.42}S_{0}^{0.3}\left (\frac{1}{nS_{x}}\right)^{0.6}}
Where:
- WT is the width of the inlet for complete capture (m),
- Q is the design flow perpendicular to the inlet (m3/s)
- S0 is the longitudinal slope ratio
- n is Manning's 'n' (between 0.012 and 0.016 for concrete, depending on surface treatment), and
- Sx is the cross slope ratio
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:: Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle R_c=1-\left ( 1-\frac{W}{W_T} \right )^{1.8}}
Where:
- Rc is the proportion of flow entering the curb cut, and
- W is the available curb cut width (m)
Example[edit]
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 m3/s.
The width of inlet to capture 100% of this flow is:: Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 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}
The proportion of water entering the bioretention cell under these flow conditions would be:: Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle R_c=1-\left ( 1-\frac{3}{9.71} \right )^{1.8}= 0.48}
48% of the 0.08 m3/s flow would enter the bioretenteion cell through the inlet as designed.
Curb cuts gallery[edit]
OPSD 605.040 Asphalt Spillway inlet to biofilter swale and road catch basin overflow outlet. County Court Blvd., Brampton, ON.
This curb cut has been sawn into existing concrete as part of a retrofit. Note the temporary (erosion log) and permanent stone erosion control measures in place. Mississauga Road, ON.
Curb cut used as a controlled overflow route from permeable pavements to a bioretention facility with monitoring well, Lake Simcoe Region Conservation Authority, Newmarket, ON.
Curb cut into a bioretention facility in Brown Deer, WI. Stone is used to reduce erosion around the inlet area. Photo credit: Aaron Volkening
Curb cut into a bioretention facility in Ajax, ON.
Stone lined inlet at IMAX site in Mississauga
The grading around this inlet prevents flow in the correct direction. i.e. from the pavement onto the grass. Not too critical in this example, as the surface is permeable pavements.
Curb cut into a rain garden on a green street in Newmarket, ON.
Curb cut leading into a small bioretention cell in Brampton, ON.
Curb cut leading to a bioswale in Brampton, ON.
