| Summary: | Sampling of urban runoff was carried out in two small catchments, which
represent residential and commercial areas in Skudai, lohor. Ten storm events for
residential and seven events for commercial catchments were analysed. Runoff
quality showed large variations in concentrations during storms, especially for SS,
BODs and COD. Concentrations of N03-N, N02-N, NH3-N, and P were also high.
Lead (Pb) was also detected in both catchments but the levels were low «0.001
mg/l). In general, the water quality was badly polluted and fell in class V of the
Interim National Water Quality Standards. The hydro graphs and pollutographs for
both catchments showed rapid increases and decreases equally rapidly. Most
pollutants were diluted as storm events progress. In most cases, the peak
concentrations preceded the peak runoff. This suggests that the pollutants were of
short distant sources/origins and the bulk of the pollutant mass arrived at the
catchment's outlet much faster than the runoff itself. For the hysteresis loop, both
catchments showed most of the parameters were characterized by clockwise
hysteresis. Only a few plots were exhibited counterclockwise and figure eight
hysteresis loop. The relative strength of the first flush for the commercial catchment
was P> COD>SS> N03-N> N02-N> BODs> NH3-N whereas for the residential
catchment was SS> COD> BODs> NH3-N> P> N03-N> N02-N. The loadings were
higher in the commercial than in the residential catchment and this was attributed to
a greater runoff volume per unit area and higher Event Mean Concentration (EMC)
in the former. Detail calibration and validation of Storm Water Management Model
(SWMM) for modeling water quantity and quality were discussed. The simulation
results, evaluated in terms of runoff depth, peak flow and the hydro graph shapes,
were satisfactorily. For the water quality modeling, the simulation results were
evaluated in terms of total load and peak load. SWMM can model SS load
reasonably weB for the residential catchment, but was not satisfactory for the
commercial catchment.
|
|---|