Description of Challenge
Natural wetlands act as a bio-filter, removing sediments and pollutants such as heavy metals from the water, and constructed wetlands can be designed to emulate these features.A constructed wetland or 'wetpark' is an artificial wetland created as a new or restored habitat for native and migratory wildlife; for treating anthropogenic discharge such as wastewater, stormwater runoff, or sewage treatment; for land reclamation after mining, refineries; or other ecological disturbances such as required mitigation for natural areas lost to a development.
Solution
Guelta, in Algeria, is the Saharan wetland. Constructed wetlands, sometimes called storm water wetlands, are shallow depressions that receive stormwater input for water quality treatment. Wetlands are typically less than 1 foot deep (although they have greater depths at the forebay and in micro-pools), and have variable micro-topography in order to promote dense and diverse wetland coverage.
Runoff from each new storm displaces runoff from previous storms, and the long residence time allows multiple pollutant removal processes to operate. The wetland environment provides an ideal environment for gravitational settling, biological uptake, and microbial activity. Constructed wetlands are the final element in the roof-to-stream runoff reduction sequence. They should only be considered for use after all other upland runoff reduction opportunities have been exhausted, and there is still a remaining water quality or Channel Protection Volume to manage.
Constructed wetlands can generate community and environmental concerns that may need to be addressed during design, such as aesthetics and habitat. Constructed wetlands can also create wildlife habitats and become an attractive community feature.
Designers should think carefully about how the the wetland plant community will evolve over time, since the future plant community seldom resembles the one initially planted.
Given the large ecological footprint of a constructed wetland, there is a strong chance that the construction process may result in extensive tree clearing. The designer should preserve mature trees during the facility layout, and he/she may consider creating a wooded wetland.
Constructed wetlands also have a moderate risk of causing stream warming. If a constructed wetland will discharge into temperature-sensitive waters, the designer should consider using the wooded wetland design to shade the water, and any extended detention storage should be released in less than 12 hours. Safety, risk, and the precautionary principle should always be considered.
Wetparks are safer than other types of ponds, although forebays and micropools should be designed with aquatic benches to reduce safety risks.
