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 in m,  
+
*''W<sub>T</sub>'' is the width of the inlet for complete capture (m),  
*''Q'' is the flow perpendicular to the inlet in 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
+
*''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]

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To completely capture linear flow travelling along a gutter perpendicular to a curb inlet, the inlet must be of width::

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::

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::

The proportion of water entering the bioretention cell under these flow conditions would be::

48% of the 0.08 m3/s flow would enter the bioretenteion cell through the inlet as designed.

Curb cuts gallery[edit]