Inlets

From LID SWM Planning and Design Guide
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Inlets are typically located at:

  • Sag points in the gutter grade
  • immediately upgrade of median breaks, crosswalks
Trench drains Curb cuts Inlet sumps Depressed drains
  • A long, covered channel that collects directs water into the BMP.
  • An excellent solution for streets where walking across the entire surface is to be encouraged. They can be designed as detectable edges or part of a detectable edge, and may be used to help define curbless or 'complete streets'.
  • Trenches may either be shallow (where runoff volume is less of an issue) or deep and covered by a metal grate. Deeper trench drains may gather sediment and require frequent maintenance.
  • Drains may be configured either perpendicular or parallel to the flow direction of the roadway, collecting runoff and directing to a single inlet in the BMP.
  • Inlet aprons or depressions increase inflow effectiveness. Aprons typically drop 50 mm into the bioretention cell, with another 50 mm drop behind the curb to maintain inflow as debris collects.
  • Gutters with steep cross slopes can be hazardous, especially to people bicycling. Curbside and protected bike lanes along concrete aprons should be at least 1.8 m to give cyclists adequate clear width from the curb and any pavement seams. Aprons could also be marked visually to indicate their perimeter.
  • Where the curb alignment along the street is straight, the curb opening may optionally have a bar across the top of the inlet.
  • For aprons into bioretention, the curb may angle into the cell to improve conveyance of gutter flow into the facility
  • A depressed concrete apron can be cast in place or retrofitted in by grinding down the existing concrete pavement.
  • An inlet sump is recommended to settle and separate sediment from runoff where a large amount of debris is expected.
  • Water drains into a catch basin, where debris settles in its sump. After pretreatement, water drains via a pipe or opening into the BMP.
  • The sump can be directly connected to a perforated underdrain pipe to distribute the flow to the bioretention or connected tree pits.
  • Sump inlets should not be sited where pedestrians will have to negotiate with them.
  • Runoff in the gutter drops into a grate-covered drain before flowing into the BMP. Drain covers must be compatible with bicycling and walking; grid covers are preferred.
  • Depressed drains are a potential solution for bioretention cells on sloped streets where directing runoff into the cell is a challenge.
  • This style of inlet can be combined with a curb cut, to maintain capacity in case debris clogs the grate.

External links[edit]

https://nacto.org/publication/urban-street-stormwater-guide/stormwater-elements/bioretention-design-considerations/inlet-design/