Modelling Sediment Behaviour in Constructed Stormwater Wetlands

<p>Urbanization leads to significant changes in stormwater quantity and quality, with the most</p><p>evident effect being the increase in the magnitude of stormwater discharge and pollutant</p><p>concentration, and the consequential negative impact on receiving waters. For example, the</p><p>increase in the quantity and rate of stormwater runoff (generated from the increased</p><p>impervious areas and the reduction in catchment's storage) results in extensive channel</p><p>erosion and an increased frequency of flooding (Wong et al., 2000). Associated with the</p><p>higher concentration of human activities in urban areas, stormwater may become highly</p><p>contaminated. Pollutants typically include suspended solids, heavy metals, nutrients,</p><p>organics, oxygen-demanding materials, pathogenic bacteria and viruses. Stormwater</p><p>quality is as varied as the sources and characteristics of the pollutants it carries. The</p><p>pollutants mainly come from transportation, industrial activities, decaying vegetation, soil</p><p>erosion, animals, fertilizer and pesticide application, dryfall (atmospheric pollution) and</p><p>general litter (Nix, 1994). However, the pollutants in stormwater may also originate from</p><p>leaking sanitary sewers, landfills, poorly operating septic systems, etc. As a result, the</p><p>receiving watercourses suffer from excessive inputs of nutrients and heavy metals, which</p><p>may lead to nuisance phytoplankton growth in the upper zone of the water bodies and</p><p>anoxia in the deeper zone. This results in a decrease in the ecosystem health and a</p><p>consequent impact on fishery and recreation values (Novotny, 2003). The recent inquiry</p><p>into Australia's urban water management commissioned by the parliament of Australia</p><p>(Commonwealth of Australia, 2002) concluded that stormwater control should become a</p><p>high priority at both state and local levels, and that it represents one of the major threats to</p><p>water quality.</p><p> </p>