[[File:Best X-section.png|thumb|Both sections a)triangular and, b)trapezoidal, are constrained within ratios of 8/1 H:V]]
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[[File:Best X-section.png|thumb|Both sections a)triangular and, b)trapezoidal, are constrained within ratios of 8:1 H:V]]
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Enhanced swales aim to both reduce the flow rate and retain a portion of the conveyed water. For these purposes the best X-section is that which maximizes the wetted perimeter. The trapzoidal channel has the marginally greater hydraulic radius, but also the greater area.
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|+ Examples worked without units, using the ratios given