Drainage engineers are increasingly installing sustainable drainage systems as required by local and statutory authorities. These have a large ecological component in their design and, particularly, aftercare. Betts Estates not only assist with ecological design input, but also provide permanent care and a solution to the problem of long term management responsibility.

SuDS are made up of one or more structures built to manage surface water runoff. They are used in conjunction with good management of the site, to prevent flooding and pollution. Control methods include prevention, filter strips/swales, permeable surfaces/filter drains, infiltration devices, and basins/ponds.

These controls are located to provide the best attenuation of surface water run-off. They also provide varying degrees of water treatment by employing the natural processes of sedimentation, filtration, adsorption and biological degradation.

Natural wetlands are “transitional areas between deep open water and dry land. They include areas of land that may be cyclically, intermittently or permanently saturated with fresh, brackish or saline water.” They support a diverse biota dependent upon the extant inundation regime.

Constructed wetlands are built because the functions that occur in natural wetlands can be harnessed to achieve the desired objectives of sustainable drainage. Although constructed wetlands are relatively straightforward to build, they are complex ecosystems. Wetland designers, builders and operators therefore need to have a broad understanding of hydrology, botany, ecology, limnology, and soil and aquatic engineering.

The success of a SuDS project largely depends on the understanding of wetland processes and the interactions between the basic elements of soil, water and biota over time.

Reed beds:

Horizontal flow beds are the most usual type and have a gradient of 1% to 2%) and a depth of 0.6 to 0.8m. The effluent flows through the bed and away to ground, sometimes through a secondary bed.

There are also vertical flow systems which operate on a batch flow basis and may be used for industrial waste effluents.

The rhizosphere (root zone) is oxygen-rich and forms a heterotrophic ecosystem in which a mosaic of aerobic and anaerobic micro-environments is achieved throughout the bed of the system. Aerobic micro-organisms occupy the rhizosphere and the bed surface/leaf litter, and the anaerobes are concentrated in the oxygen-free zones away from roots and the soil surface.

We have constructed and operated artificial wetland systems. Good design, a clear understanding of the biological and ecological science, and especially adequate maintenance and monitoring are important factors.

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