Changes

===Topography===

===Topography===

Filter strips are best used to treat runoff from ground-level impervious surfaces that generate sheet flow (e.g., roads and parking areas). The recommended filter strip slope is between 1 - 3 %. Though steeper slopes increase the likelihood of erosion, incorporation of multiple level spreaders in series or terraces can counteract this (see below).

Filter strips are best used to treat runoff from ground-level impervious surfaces that generate sheet flow (e.g., roads and parking areas). The recommended filter strip slope is between 1 - 3 %. Though steeper slopes increase the likelihood of erosion, incorporation of multiple level spreaders in series or terraces can counteract this (see below).

===Flow Path Length Across Impermeable Surface===

===Flow path length across impermeable surface===

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A limiting design factor is that the maximum flow path length across the impermeable surface must be < 25 m, as flow tends to concentrate ≥ 25 m over an impermeable surface.<ref>Claytor, R. and T. Schueler. 1996. Design of Stormwater Filtering Systems. Center for Watershed Protection. Ellicott City, MD.</ref>.  

A limiting design factor is that the maximum flow path length across the impermeable surface must be < 25 m, as flow tends to concentrate ≥ 25 m over an impermeable surface.<ref>Claytor, R. and T. Schueler. 1996. Design of Stormwater Filtering Systems. Center for Watershed Protection. Ellicott City, MD.</ref>.