Wetlands play an important role in managing water in urban catchment areas. The figure below shows a generic design for a constructed wetland.
Vegetation within the wetland can be broken up into zones perpendicular to the flow. These zones refer to the depth of water and appropriate species to be selected to optimise the success of the system.
All species used in vegetation, including both aquatic and terrestrial, should be indigenous and local provenance.
In areas of predictable low rainfall patterns and where there is also a high evaporative loss due to wind sheer, the wetland should use a vegetation sequence such that there is sustainable water depths in deep and submerged marsh areas during drawn down, as illustrated below.
An example
Constructed wetlands can be small scale. A wetland has been constructed at Urrbrae Agricultural School in Adelaide, South Australia to treat effluent water from a nursery. Water used to irrigate plants in pots and trays collects considerable nutrient. A small wetland can deal with this waste; although the design is somewhat different to the above, the principles are the same. In winter, the growth in the wetland can be harvested and returned to the muching heap.
The inlet tank
Inlet outflow sperader and Stage 1 plants (knobbly club rush and sedges).
Stage 2 plants - Marsilea spp - Nardoo. Used by indigenous people to make bread.This photograph was taken in summer when growth in the wetland is at its peak. Contrast this with the last figure below which was taken in winter.
The figure below shows the wetland in late winter, immediately after the harvest of plants. It is now ready for a new season.
Please use the word processor in your Google Docs account to write a short article describing how you might adapt some of the principles outlines here to small urban sites.
