Curb cuts

From LID SWM Planning and Design Guide
Jump to navigation Jump to search

Sizing[edit]

Error in widget WolframAlpha: Unable to load template 'wiki:WolframAlpha'

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

Curb cuts gallery[edit]