Curb cuts

From LID SWM Planning and Design Guide
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Sizing[edit]

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 in m,
  • Q is the flow perpendicular to the inlet in m3/s
  • S0 is the longitudinal slope
  • n is Manning's 'n' (between 0.012 and 0.016 for concrete, depending on surface treatment),
  • Sx is the cross slope

Where the intention is to capture only a proportion of the flow, the ratio of flow entering the curb inlet may be calculated::

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]