Ponds and Sedimentation Basins are simply basins or waterbodies (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.
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The initial 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.
A conceptual diagram of the pond, detention basin and sedimentation basin properties in MUSIC is presented below:
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Conceptual diagram of pond, detention basin and sedimentation basin properties.
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The location name will be displayed under the pond, detention basin or sedimentation basin node icon on the main worksheet.
Inlet Properties
The Inlet Properties define the physical characteristics of the inlet section of the pond, detention basin or sedimentation basin.
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Exfiltration from the permanent pool of a pond, detention basin or sedimentation basin into the underlying soil can be modelled by defining the exfiltration rate (mm/hr). Representative exfiltration rates for different soil types are provided in the table below. The water that seeps from the permanent pool of the pond, detention basin or sedimentation basin is lost from the catchment, and cannot re-enter the system downstream. Contaminants in the water that is lost to exfiltration are removed from permanent pool, along with the exfiltrated water and are also lost from the catchment. Representative exfiltration rates for different soil types are shown in the following table.
| Soil Type | Median particle size (mm) | Saturated Hydraulic Conductivity | |
|---|---|---|---|
| (mm/hr) | (m/s) | ||
| Gravel | 2 | 36000 | 1x10-2 |
| Coarse sand | 1 | 3600 | 1x10-3 |
| Sand | 0.7 | 360 | 1x10-4 |
| Sandy loam | 0.45 | 180 | 5x10-5 |
| Sandy clay | 0.01 | 36 | 1x10-5 |
Evaporative Loss
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.
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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 Equivalent Pipe Diameter is defined in mm. 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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Overflow Weir Width
Defines the width of the overflow weir for the pond, detention basin or sedimentatin basin. The overflow weir will only start to carry a discharge of water once the depth in the pond reaches the Extended Detention Depth defined above. The Overflow Weir Width is defined as a length in metres.
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The advanced properties section (opened using the ‘More’ button) of the pond, detention basin or sedimentation 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.
Orifice Discharge Coefficient
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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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