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<br />5.6
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<br />Chapter 5: Infiltration Trenche.
<br />
<br />l
<br />
<br />DESIGN 3:
<br />
<br />Swale De.i~ns (Figure 5.4). Low density residential runoff (5-15%
<br />impervious) can be treated through 8 series of surface t:renches
<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%. Otherwise, concentrated flows will develop that
<br />might erode the swales and contamina1:e. the trench. In addit.ion)
<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 "short-circuiting" and increase the volume
<br />of runoff exfiltrated by ehe trench. The slope of the trench
<br />should be as close -Co zero as feasible, and should have sideslopes
<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 />Side View
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<br />Auncff
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<br />Road
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<br />Remon
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<br />Permeable Filler Fabric: Lines 5ide:s
<br />and Abo alOne Fool Treflch Depth
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<br />6 Inch Sand layiltr
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<br />E::dlltra1lon
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