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Water Science & Technology Vol 52 No 9 pp 125–132 © IWA Publishing 2005

Runoff quality and pollution loadings from a tropical urban catchment

Z. Yusop*, L.W. Tan**, Z. Ujang***, M. Mohamed**** and K.A. Nasir*****

*Institute of Environmental and Water Resources Management (IPASA) Universiti Teknologi Malaysia, Skudai, 81310, Johor, Malaysia, (E-mail: zulyusop@utm.my)
**Faculty of Engineering, Kolej Universiti Teknologi Tun Hussein Onn, 86400 Parit Raja, Batu Pahat, Johor, Malaysia
***Institute of Environmental and Water Resources Management (IPASA) Universiti Teknologi Malaysia, Skudai, 81310, Johor, Malaysia, (E-mail: zulyusop@utm.my)
****Institute of Environmental and Water Resources Management (IPASA) Universiti Teknologi Malaysia, Skudai, 81310, Johor, Malaysia, (E-mail: zulyusop@utm.my)
*****Institute of Environmental and Water Resources Management (IPASA) Universiti Teknologi Malaysia, Skudai, 81310, Johor, Malaysia, (E-mail: zulyusop@utm.my)


ABSTRACT
Runoff quality draining from 17.14 km2 urban catchment in Johor Bahru, Malaysia, was analysed. The land-use consists of residential (30.3%), agricultural (27.3%), open space (27.9%), industrial (8.1%) and commercial (6.4%) areas. Three storm events were sampled in detail. These storms produced stormflow between 0.84 mm and 27.82 mm, and peakflow from 2.19 m3/s to 42.36 m3/s. Water quality showed marked variation during storms especially for TSS, BOD and COD with maximum concentrations of 778 mg/l, 135 mg/l and 358 mg/l, respectively. Concentrations of TOC, DOC, NH3-N, Fe and level of colour were also high. In general, the river quality is badly polluted and falls in Class V based on the Malaysian Interim National Water Quality Standards. Event Mean Concentrations (EMC) for various parameters varied considerably between storms. The largest storm produced higher EMC for TSS, NO3-N and SS whereas the smaller storms tend to register higher EMC for BOD, COD, NH3-N, TOC, Ca, K, Mg, Fe and Zn. Such variations could be explained in terms of pollutant availability and the effects of flushing and dilution. Based on a three-month average recurrence interval (ARI) of rainfall, the estimated event loadings (ton/ha) of TSS, BOD, COD, TOC, NH3-N and NO3-N were 0.055, 0.016, 0.012, 0.039, 0.010, 0.0007 and 0.0002, respectively. Heavy metals present in trace quantities. Storms with 3 months ARI could capture about 70% of the total annual loads of major pollutants. Keywords Average recurrence interval; event mean concentration; pollutant loading; runoff quality

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