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<br />5.6
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<br />Chapter 5: Infiltration Trenches
<br />
<br />l
<br />
<br />DESIGN 3:
<br />
<br />Swale Desi1;:ns (Figure 5.4). Low density residential runoff (5-15%
<br />impervious) can be ~reated ~hrough a series of surface t~enches
<br />located in swale drainage systems. The major design requirement is
<br />that the longitudinal slope of the swale collection system should
<br />neVer exceed 5%. OtherwiseJ concentrated flows will develop that
<br />might erode the swales and contaminate the trench. In addition.
<br />concentrated flows may pass around or over the surface of the
<br />trench and never infiltrate. An earthen check dam or railroad tie
<br />placed perpendicularly to the flow path, on the downstream side of
<br />the trench ~ can prevent Ifshort-circuitingll and increase the volume
<br />of runoff exfiltrated by the trench. The slope of the trench
<br />should be as close to zero as feasible, and should have sides lopes
<br />of 5:1 (h:v) or less.
<br />
<br />Figure 5.4: Swale/Trench Design
<br />
<br />Top View
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<br />/ t.Of
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<br />Side View
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<br />Runoff
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<br />Road
<br />
<br />......
<br />Permeable Filter Fabric: Linn Side:s
<br />and Also at One Foot ltench Deplh
<br />
<br />6 Inch Sand Layer
<br />
<br />e.-filtration
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