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Ponds and Sedimentation Basins are simply basins or 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.

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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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Tip Box

 Use the Notional Detention Time display to check whether the designed pond properties (volume and Equivalent Pipe Diameter) give approximately the required detention time. For more information, refer to Wong et al. (1998).

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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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