Ponds and Sedimentation Basins are simply basins or waterbodies water bodies (eg. ponds, retarding basins) reliant on the physical settling of suspended solids as the principal treatment mechanism and can reduce peak flows through detaining a volume of the runoff and allowing for slower release during and after the event. Other mechanisms associated with phytoplankton assimilation of soluble nutrients and ultra-violet disinfection are currently not included in the modelling algorithm.
MUSIC provides separate Treatment Nodes for Ponds, Detention Basins and Sedimentation Basins, which are modelled in exactly the same way as each other, but have different default k, C* and CSTR values (refer to Appendix G : - Selecting Appropriate k and C* Values for advice on selecting appropriate k, C* and CSTR values for particular treatment measures). Neither the Pond or nor the Sedimentation Basin treatment nodes include a provision to enter an inlet pond volume. The Pond node is similar to the macrophyte cell in a wetland, but with different default k, C* and CSTR values to represent their different water quality treatment behaviour.
Pond, Detention and Sedimentation Basin Properties
The initial properties properties dialogue box contains the parameters that describe the basic physical characteristics of the pond, detention basin or sedimentation basin. A description of each of the parameters is given below.
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Evaporation from the permanent pool of a pond, detention basin or sedimentation basin can be modelled by defining the evaporative loss rate, defined as a percentage of the daily Potential Evapotranspiration data contained in the Meteorological Template used to create the model. The water that evaporates from the permanent pool of the pond or sedimentation basin is lost from the catchment. Contaminants in the water that is lost to evaporation remain within the permanent pool.
The button 
allows you to estimate the surface area of the sedimentation basin. Clicking it opens the Estimate Parameter Properties dialogue box, which is explained further below.
Outlet Properties
The physical characteristics of the outlet pipe and weir are defined in this section of the dialogue box.
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Defines the equivalent diameter of the outlet pipe (this may not be the diameter of the pipe itself, but the equivalent diameter of its orifices). The outlet pipe is notionally set with an invert at the standing water level of the permanent pool. The pond, detention basin or sedimentation basin dialogue box will display the notional detention time, based on the pond or basin volume, and the Equivalent Pipe Diameter.
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A custom pipe flow, weir flow and storage relationship can be specified to represent custom outlet and storage configurations for ponds, detention basins and sedimentation basins. The outflow relationships can either replace or add to the standard MUSIC outflows. More information on how to use the custom outflow and storage facility is available in this section.
Estimate Parameters
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The advanced properties section (opened using Advanced Tab) of the sedimentation basin, pond or detention basin displays the parameters that describe the hydraulic characteristics for the outflow structures, and the parameters that describe the treatment process in the pond, detention basin or sediment basin as shown below.
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Orifice Discharge Coefficient
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The overflow weir carries a discharge when the water level in the pond or sedimentation basin exceeds the Extended Detention Depth. The overflow weir is modelled as a sharp broad crested weir whose discharge equation is given by:
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Note that for a sedimentation basin, the default values for k, C* and C** for each of the constituents are as shown in the diagram above.
Threshold Hydraulic Loading for C**
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