Filter Strips - Overview

Made from dense vegetation – typically grass – filter strips are uniformly sloped sections used to pre-treat low velocity surface water run-off from linear lengths of hard surfacing.

The lengths of vegetation capture sediments and soluble pollutants from roads, car parks and pavements allowing the remaining water to infiltrate downward into the soil. Discharging from the site in a uniform manner, the water is treated and its quality improved. Filter strips can also be effective as a combined SuDS solution with a filter drain and/or silt trap.

Whilst typically used to provide pre-treatment of surface water flows from impermeable surface areas, prior to discharge into SuDS ‘collector’ elements, filter strips reduce the reduction of flow velocities as water passes through the surface vegetation, encouraging silt deposition across the filter strip; which is then trapped by the vegetation. Where surface water is allowed to infiltrate within the surface and sub-surface soils, further treatment can be achieved through biochemical processes – the biochemical process driven by the type of planting used and the active micro-organisms present within the engineered soils.