n Civil Engineering = Siviele Ingenieurswese - An early performance analysis of a bio-swale and litter-silt-traps as components of sustainable drainage systems : environmental engineering




During the construction of the Kraaifontein (Integrated) Waste Management Facility (KWMF) in Cape Town, alternative stormwater management options, which included litter-silt-traps and a bio-swale, were implemented. Stormwater runoff from the site is collected in several litter-silt-traps and discharged into the bio-swale, which is located at the lowest corner of the site. Polished stormwater subsequently discharges into an existing retention pond downstream of the site. The bio-swale is categorised as a 'local control' Sustainable Drainage Systems (SuDS) option, and is the amalgamation of selected properties of two local control SuDS options, namely bio-retention areas and swales. As a result of the unique waste operations onsite the quality of stormwater that is discharged into the bio-swale is highly contaminated, in some instances replicating landfill leachate at over 17 000 mg COD/ℓ. Stormwater samples were taken at four six-monthly intervals at the beginning and end of the Cape's wet and dry seasons. The results clearly demonstrate the efficacy of these SuDS options in reducing, , heavy metals, suspended solids, total phosphorous and COD, with over 80% removal efficiencies. These results have exceeded the treatment requirements stipulated in the City's latest stormwater management policy.


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