Design note 3 - Source nodes

See Melbourne Water’s MUSIC Guidelines, Chapter 5.

Soil parameters should be adopted as follows:

  • Soil Store Capacity = 120 millimetres
  • Field Capacity = 50 millimetres

The use of alternate soil parameters should be based on calibration to observed flows, supported with an accompanying report of the calibration and is subject to agreement in writing by the City.


Pollutant concentration data

This section supersedes the corresponding section in the Melbourne Water MUSIC Guidelines (2018).

Catchments may be represented using a lumped catchment or split catchment approach, as follows;

  • The lumped catchment approach is suitable for most development applications and modelling of typical catchments.
  • The split catchment approach may be used for modelling systems with treatment focussed on particular surface types.

Lumped catchment

Three general types of land use are available in source nodes:

  • Urban
  • Agricultural
  • Forest

Stormwater pollutant concentrations were estimated for use in MUSIC based on a study of worldwide data (Duncan, 1999) and these provide the basis (with minor updates) for the default parameters provided in the model for these land uses.

It is required that these default parameters are used for the Urban (Mixed surface type/land use), Agricultural and Forest node pollutant concentrations unless written permission is provided by the City or the split catchment approach below is adopted.

Surface type/land use combinations other than ‘Mixed’ available by default in MUSIC for the Urban source node are not recommended for use at this time.


Split catchment

It is recognised that pollutant concentrations may be significantly different for road and roof surface types and that some stormwater management responses may focus strongly on one or both of these. Separate source nodes representing different surface types may be adopted to provide more accurate modelling in the following circumstances:

  • Roof water harvesting (rainwater tanks).
  • Direct streetscape treatments.
  • Where the catchment has a distribution of surface types that is very different to a typical urban area (e.g. where the proposed catchment is entirely or mostly a road).

Where the split catchment surface types approach is adopted, the stormwater pollutant concentrations listed in should be used. These should be applied consistently to represent all urban catchment areas and not mixed in the same model with nodes using the Urban (Mixed surface type/land use).
Table 1: Pollutant concentration data for source nodes where surface types are split.


Pollutant
Surface type Storm flow Base flow
Mean
(log mg/L)
SD
(log mg/L)
Mean
(log mg/L)
SD
(log mg/L)
Total suspended solids (TSS) Roof 1.301 0.333 n/a* n/a
Road 2.431 0.333 n/a n/a
All other urban 1.882 0.333 0.96 0.401
Total phosphorus (TP) Roof -0.886 0.242 n/a n/a
Road -0.301 0.242 n/a n/a
All other urban -0.680 0.242 -0.731 0.360
Total Nitrogen (TN) Roof 0.301 0.205 n/a n/a
Road 0.342 0.205 n/a n/a
All other urban 0.224 0.205 0.346 0.309

Source: Fletcher, 2007, Background Study for the Revision of Melbourne Water’s MUSIC Input Parameter Guidelines, unpublished
*n/a indicates that base flow does not occur from these surfaces
Note that the parameters available under zoning/surface type by default in MUSIC may NOT correspond with the above parameters and the user is responsible for ensuring the correct parameters are used.


Serial correlation

The serial correlation (R squared) must be set to zero for TSS, TP and TN for analysis of stormwater quality.


Stochastic Versus mean generated data

Stochastically generated pollutant concentrations must be used.


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Page last updated: Wednesday, 18 December 2019

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