Design Specification No 2: Sheet Flow to a Vegetated Filter Space or Conserved Open Space

Filter strips are vegetated areas that treat sheet flow delivered from adjacent impervious and managed turf areas by slowing runoff velocities and allowing sediment and attached pollutants to settle and/or be filtered by the vegetation. The two design variants of filter strips are

  1. conserved open space
  2. designed Vegetated Filter Strips.

The design, installation, and management of these design variants are quite different, as outlined in this specification.

Grass Channel
Grass channels can provide a modest amount of runoff filtering resulting in less runoff than storm drain inlets.

In both instances, stormwater must enter the filter strip or conserved open space as sheet flow. If the inflow is from a pipe or channel, an engineered level spreader must be designed in accordance with the criteria contained herein to convert the concentrated flow to sheet flow.