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Each component of runoff is calculated using the information above and a daily time-step. Each component is then disaggregated to the required time-step, using the detailed rainfall pattern and a technique appropriate to that component. For more information on disaggregation see Appendix A: Rainfall-Runoff Modelling.
Water Quality Parameter Dialogue Boxes
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For source nodes, each land use/zoning type has appropriate base flow and storm flow pollutant concentrations for that zoning (eg. rural residential) or surface type (eg, sealed roads, unsealed roads). The selection of Land Use/Zoning Type on Source Tab changes the default values displayed on Total Suspended Solids, Total Phosphorous and Total Nitrogen Tabs. Prior to MUSIC version 6.2, MUSIC had three source nodes, Urban, Agricultural and Forest. The 'mixed' Zoning/Surface type contains the same pollutant concentration parameters as the prior default 'Urban' values. For all other Zoning/Surface types, the pollutant concentration parameters are Sydney Catchment Authority (2012).
Table 1. Default pollutant concentrations for each source node
Source Node Type | Zoning/Surface Type | Pollutant Concentration (log mg/L) | |||||||||||
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| Total Suspended Solids | Total Phosphorus | Total Nitrogen | |||||||||||
| Base Flow | Storm Flow | Base Flow | Storm Flow | Base | Storm | ||||||||
| Mean | Std Dev | Mean | Std Dev | Mean | Std Dev | Mean | Std Dev | Mean | Std Dev | Mean | Std Dev | ||
| Agricultural | - | 1.40 | 0.13 | 2.30 | 0.31 | -0.88 | 0.13 | -0.27 | 0.30 | 0.074 | 0.130 | 0.59 | 0.26 |
| Forest | - | 0.90 | 0.13 | 1.90 | 0.20 | -1.50 | 0.13 | -1.10 | 0.22 | -0.14 | 0.13 | -0.075 | 0.240 |
Urban | Mixed | 1.10 | 0.17 | 2.20 | 0.32 | -8.20 | 0.19 | -0.45 | 0.25 | 0.32 | 0.12 | 0.42 | 0.19 |
| Roof | 1.10 | 0.17 | 1.30 | 0.32 | -8.20 | 0.19 | -0.89 | 0.25 | 0.32 | 0.12 | 0.30 | 0.19 | |
| Sealed Road | 1.20 | 0.17 | 2.43 | 0.32 | -8.50 | 0.19 | -0.30 | 0.25 | 0.11 | 0.12 | 0.34 | 0.19 | |
| Unsealed road | 1.20 | 0.17 | 3.00 | 0.32 | -8.50 | 0.19 | -0.30 | 0.25 | 0.11 | 0.12 | 0.34 | 0.19 | |
| Eroding gullies | 1.20 | 0.17 | 3.00 | 0.32 | -8.50 | 0.19 | -0.30 | 0.25 | 0.11 | 0.12 | 0.34 | 0.19 | |
| Revegetated land | 1.15 | 0.17 | 1.95 | 0.32 | -1.22 | 0.19 | -0.66 | 0.25 | -0.05 | 0.12 | 0.30 | 0.19 | |
| Quarries | 1.20 | 0.17 | 3.00 | 0.32 | -0.85 | 0.19 | -0.30 | 0.25 | 0.11 | 0.12 | 0.34 | 0.19 | |
| Residential | 1.20 | 0.17 | 2.15 | 0.32 | -0.85 | 0.19 | -0.60 | 0.25 | 0.11 | 0.12 | 0.30 | 0.19 | |
| Commercial | 1.20 | 0.17 | 2.15 | 0.32 | -0.85 | 0.19 | -0.60 | 0.25 | 0.11 | 0.12 | 0.30 | 0.19 | |
| Industrial | 1.20 | 0.17 | 2.15 | 0.32 | -0.85 | 0.19 | -0.60 | 0.25 | 0.11 | 0.12 | 0.30 | 0.19 | |
Rural residential | 1.15 | 0.17 | 1.95 | 0.32 | -1.22 | 0.19 | -0.66 | 0.25 | -0.05 | 0.12 | 0.30 | 0.19 | |
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There are two options available for defining pollutant concentration in both the surface and baseflow components of the runoff:
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| Time-step | Autocorrelation coefficient | |
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| Baseflow | Stormflow | |
| 6-min | 0.94 | 0.95 |
| 12-min | 0.82 | 0.93 |
| 30-min | 0.51 | 0.84 |
| 1-hour | 0.41 | 0.77 |
| 3-hour | 0.37 | 0.62 |
| 6-hour | 0.35 | 0.50 |
| Day | 0.31 | 0.27 |
It is important to note that the autocorrelation coefficient will not significantly affect the treatment train effectiveness produced by music, but simply ensures that the variation over time in concentrations during storm events and baseflow conditions is more ‘realistic’. Depending on the time-step and coefficient used, there can be variations in mean annual loads for the same model run on different computers, however the maximum difference is usually within 10% of the previous run.
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