Difference between revisions of "Curb cuts"

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Curb cuts are just one form of BMP [[Inlets|inlet]]. They are well suited to retrofit scenarios and to collect runoff from catchments with relatively gentle longitudinal slope, and/or a greater cross slope. 
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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 increases rapidly on steeper roads.
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==Sizing==
 
==Sizing==
 
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{{#widget:WolframAlpha|id=664012476f5d9635d57cd58920e763e6}}</div>
 
{{#widget:WolframAlpha|id=664012476f5d9635d57cd58920e763e6}}</div>
 
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Inlet width is directly proportional to longitudinal slope; the required curb cut increases rapidly along steeper roads.
 
 
 
 
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::
 
<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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*''W'' is the available curb cut width (m)}}
 
*''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 small depressed section.  
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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.  
 
<math>   
 
<math>   
 
 
  
  

Revision as of 19:29, 31 October 2017

Curb cuts are just one form of BMP inlet. 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 increases rapidly on steeper roads.

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 (typically between 0.015 and 0.04)

Where 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)

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.

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

48% of the 0.08 m3/s (i.e. 0.038 m3/s) would enter the bioretenteion cell through the inlet as designed.

Curb cuts gallery[edit]