Modelling Sediment Behaviour in Constructed Stormwater Wetlands

Urbanization leads to significant changes in stormwater quantity and quality, with the most

evident effect being the increase in the magnitude of stormwater discharge and pollutant

concentration, and the consequential negative impact on receiving waters. For example, the

increase in the quantity and rate of stormwater runoff (generated from the increased

impervious areas and the reduction in catchment's storage) results in extensive channel

erosion and an increased frequency of flooding (Wong et al., 2000). Associated with the

higher concentration of human activities in urban areas, stormwater may become highly

contaminated. Pollutants typically include suspended solids, heavy metals, nutrients,

organics, oxygen-demanding materials, pathogenic bacteria and viruses. Stormwater

quality is as varied as the sources and characteristics of the pollutants it carries. The

pollutants mainly come from transportation, industrial activities, decaying vegetation, soil

erosion, animals, fertilizer and pesticide application, dryfall (atmospheric pollution) and

general litter (Nix, 1994). However, the pollutants in stormwater may also originate from

leaking sanitary sewers, landfills, poorly operating septic systems, etc. As a result, the

receiving watercourses suffer from excessive inputs of nutrients and heavy metals, which

may lead to nuisance phytoplankton growth in the upper zone of the water bodies and

anoxia in the deeper zone. This results in a decrease in the ecosystem health and a

consequent impact on fishery and recreation values (Novotny, 2003). The recent inquiry

into Australia's urban water management commissioned by the parliament of Australia

(Commonwealth of Australia, 2002) concluded that stormwater control should become a

high priority at both state and local levels, and that it represents one of the major threats to

water quality.