Difference between revisions of "Level spreaders"

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Level spreaders should conform to the following design criteria in order to ensure non-erosive sheet flow into vegetated areas such as [[vegetated filter strips]][[swales]] or forested conservation areas<ref>Hathaway, J. M., & Hunt, W. F. (2006). Level Spreaders : Overview , Design , and Maintenance.</ref>.
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[[File:Levelspread.jpg|thumb|This clever design incorporates a level spreading device after a [[curb cut]] has narrowed the flow path. This kind of treatment train approach would provide an opportunity to provide [[pretreatment]] at the point of concentration. Photo credit: [https://www.pca.state.mn.us/featured/when-it-rains-it-flows MPCA] ]] 
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[[File:Level spreader diagram.jpg|thumb|Diagram from Wikimedia commons. Credit: U.S. Army Corps of Engineers, Construction Engineering Research Laboratory]]
  
The length of the level spreader should be determined by the type of filter area and the design flow:
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Level spreaders should conform to the following design criteria in order to ensure non-erosive sheet flow into vegetated areas such as [[vegetated filter strips]], [[Bioretention|bioretention]], [[swales]] or forested conservation areas<ref>Hathaway, J. M., & Hunt, W. F. (2006). Level Spreaders : Overview , Design , and Maintenance.</ref>.
* 1.4 m of level spreader length per every 0.01 cubic meter per second (cms) of inflow for discharges to a filter strip or turf conservation area;
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* 4.3 m of level spreader length per every 0.01 cms of inflow when the spreader discharges to a forested conservation area.
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The length of the level spreader should be determined by the design storm inflow rate and type of landscape downstream:
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* 1.4 m of level spreader length per every 0.01 m³/s of inflow when draining to a [[vegetated filter strips|vegetated filter strip]], [[Bioretention| bioretention]], [[Swale| swale]] or grassed area;
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* 4.3 m of level spreader length per every 0.01 m³/s of inflow when draining to a forested conservation area.
 
* The minimum level spreader length is 4 m and the maximum is 40 m.
 
* The minimum level spreader length is 4 m and the maximum is 40 m.
* The level spreader lip should be concrete, wood or pre-fabricated metal, with a well anchored footer, or other accepted rigid, non-erodible material.
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* The level spreader lip should be concrete, wood or pre-fabricated metal.
* The ends of the level spreader section should be tied back into the slope to avoid scouring around the ends of the level spreader; otherwise, short-circuiting of the facility could create erosion.
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* The ends of the level spreader section should be tied back into the slope to avoid [[overflow]] scouring or erosion around the ends.
* The width of the level spreader channel on the up-stream side of the level lip should be three times the diameter of the inflow pipe, and the depth should be 20 cm or one-half the culvert diameter, whichever is greater.
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* The width of the level spreader should be the greater of 300 mm or three times the diameter of the inflow pipe.
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* The depth should be the greater of 200 mm or half the inflow pipe diameter.
 
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[[Category:Pretreatment]]

Latest revision as of 18:02, 23 March 2022

This clever design incorporates a level spreading device after a curb cut has narrowed the flow path. This kind of treatment train approach would provide an opportunity to provide pretreatment at the point of concentration. Photo credit: MPCA
Diagram from Wikimedia commons. Credit: U.S. Army Corps of Engineers, Construction Engineering Research Laboratory

Level spreaders should conform to the following design criteria in order to ensure non-erosive sheet flow into vegetated areas such as vegetated filter strips, bioretention, swales or forested conservation areas[1].

The length of the level spreader should be determined by the design storm inflow rate and type of landscape downstream:

  • 1.4 m of level spreader length per every 0.01 m³/s of inflow when draining to a vegetated filter strip, bioretention, swale or grassed area;
  • 4.3 m of level spreader length per every 0.01 m³/s of inflow when draining to a forested conservation area.
  • The minimum level spreader length is 4 m and the maximum is 40 m.
  • The level spreader lip should be concrete, wood or pre-fabricated metal.
  • The ends of the level spreader section should be tied back into the slope to avoid overflow scouring or erosion around the ends.
  • The width of the level spreader should be the greater of 300 mm or three times the diameter of the inflow pipe.
  • The depth should be the greater of 200 mm or half the inflow pipe diameter.

  1. Hathaway, J. M., & Hunt, W. F. (2006). Level Spreaders : Overview , Design , and Maintenance.