Anchor Urban Runoff Generation Urban Runoff Generation
Urban Runoff Generation
| Urban Runoff Generation | |
| Urban Runoff Generation |
The majority of stormwater runoff in urban catchments is generated from the impervious surfaces. Baseflow, influenced by sub-surface soil moisture and groundwater levels, is less dominant in urban catchments as is evident from the "flashy" nature of urban stormwater hydrographs.
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Figure 1. Conceptual Rainfall-Runoff Model adopted for MUSIC (after Chiew & McMahon, 1997)
Urban Pollutant Load relationships
A comprehensive review of worldwide stormwater quality in urban catchments was undertaken by Duncan (1999). This review supplemented by local data specific to regional applications has formed the basis for default values of event mean concentrations for Total Suspended Solids (TSS), Total Phosphorus (TP) and Total Nitrogen (TN) adopted in MUSIC. These water quality constituents, together with gross pollutants are the only pollutants fully modelled in MUSIC (ie. with appropriate generation and treatment parameterisation). This current version of MUSIC includes the ability to
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"swap" a pollutant for another, and allows simulation of a wider range of pollutant types, however, this should be done where sufficient data is available to characterise both generation and treatment performance.
Analysis by Duncan (1999) found
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even mean concentrations of TSS, TP and TN to be approximately log-normally distributed for a range of different urban land-use. A sample normal probability plot (for TSS) is shown in Figure 2 below. The means of the Dry Weather Concentration (DWC) and Event Mean Concentration (EMC) data have been adopted as default parameters in the model. The standard deviations of the DWC and EMC data reflect the influence of both spatial and temporal factors and are considered to be larger than that applicable at any individual site. Therefore default standard deviations of dry weather and (storm) event mean concentrations of TSS, TP and TN adopted in the model are scaled by 67% and 33% for event flow and dry weather (baseflow) parameters respectively, based on limited analysis of stormwater quality data for an urban catchment in Melbourne.
You can change the parameters of the log-normal distribution of each pollutant type, (refer to Figure 3 to Figure 5 and Duncan (1999) for more information). MUSIC uses a stochastic generation approach, deriving concentrations for TSS, TP and TN at each time-step from the distribution described by the mean and standard deviation for each.
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