Monitoring stormwater quality through a series of natural andconstructed treatment devices. A case study from Brisbane, subtropicalAustralia

摘要

Stormwater best management practices include the installation of a variety of waterquality improvement devices to treat urban stormwater runoff. Several of these devicesoccur within a 1km stretch of an upper urbanised creek catchment. The main channelisedstream flows into a sediment basin, then into a constructed wetland, followed by asecond deeper wetland. The latter also receives stormwater through a piped drainagesystem after it passes through a below ground GPT. A minor tributary receivesstormwater through a piped drainage system, which also passes through a GPT beforeentering a natural densely vegetated riparian wetland. The water from both tributariesconverges and flows downstream through a natural channel and series of lagoons. Theaims of the research project were to determine spatial and temporal changes in pollutantconcentration during wet and dry weather and; to assess the effectiveness of the"treatment train" in removing nutrients and suspended solids.Water quality parameters monitored included total and volatile suspended solids andnutrient speciation. TSS in stormwater runoff entering the sediment basin within 12 h ofstorm event was highly variable and TVS was about 25%. There was little reduction inTSS along the treatment train. However, within 24 hours of a storm event TSS instormwater had decreased to background concentrations, but was still higher in thewetlands. Higher TSS in the wetlands also occurred in dry weather suggestingresuspension ( caused by ducks )of both sediment and organic particulates (TVS wasabout 50%). TSS was consistently reduced in the downstream natural stream channel.During storm events NH_4 increased in Wetland 2, but NO_3 and PO_4 were reduced.Highest concentrations of NH_4, NO_x, PO_4 in both wet and dry weather were from pipedoutlets (in particular those from the below ground GPT's). In dry weather, NO_3concentrations were reduced in the wetlands and natural stream channel.Our study concluded that during storm events the treatment train has little effect on theremoval of TSS due to the high flow and short detention times, but some reduction innutrients did occur. Nutrients in piped drainage were always higher than in the openstream channel suggesting periphyton in the channelised streambed were probablyeffective in removing dissolved nutrients. The 600 m length of remnant natural channel,lagoons and associated vegetation was effective for water quality improvement in poststorm and dry weather. This serves as a reminder that the retention of natural streamchannels and buffers of riparian vegetation are an integral component of BestManagement Practice for urban stormwater treatment in many catchments.