Waitakere City Vehicle Testing Station Raingarden -Stormwater Quality Monitoring and Performance

摘要

The Waitakere City Vehicle Testing Station raingarden was monitored to assess stormwater quality runoff from a 3000 m~2 carpark and to assess treatment efficiency of the raingarden. Continuous flow records were obtained over a 247 day monitoring period and stormwater quality samples were collected from eight rainfall events. Contaminants monitored included total suspended solids (TSS), dissolved zinc and copper (DZn and DCu), particulate zinc and copper (PZn and PCu) and total petroleum hydrocarbons (TPH). TPHs were not detected in the first four events, but following modifications to the sampling procedure, samples from the seventh event showed that TPHs were present. Monitoring data were supplemented with stormwater quality modelling using STORMQUAL to estimate stormwater quality yields and treatment efficiencies. Sensitivity of predicted loads to the percolation rate of the media was assessed. Carpark stormwater quality yields were computed: 32.1 kg of TSS (154 kg ha~(-1) a~(-1)), 90.2 g of TZn (0.432 kg ha~(-1) a~(-1)) and 10.2 g of TCu (0.0487 kg ha~(-1) a~(-1)). Despite these relatively small loads, high retention efficiencies were achieved: 83% for TSS, 80% for TZn and 51% for TCu. Contaminant loads vary with the percolation rate of the media and sediment build-up in the upper layer of the media. The sensitivity results show that contaminant retention efficiency for TSS and other contaminants varies with percolation rate.