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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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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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There is an option to re-use water from the pond, detention basin or sediment basin, by specifying a demand. Refer to Water Re-use from Treatment Nodes for further information about this.


You can use the node water balance report to obtain basic information on the overall water balance at these nodes, including basic information on reuse at the node.  You can view this in results manager.

A reporting window will then be presented showing the water balances for various inflows and outflows at the  sedimentation basin as shown below.


It is possible to  view or save various flows and water quality as below  for the pond or sedimentation or detention basin:

  • inflow rate and water quality
  • outflow rate and water quality
  • low and high flow bypass rate and water quality
  • overflow rate and water quality
  • total outflow rate (sum of outflow, bypasses and overflow) and water quality
  • computed water levels and storage
  • water re-use demand and actual volume supplied.

You need to select them to record before you run. 

Advanced Pond, Detention Basin or Sedimentation Basin Properties

The advanced properties section (opened using the ‘More’ buttonAdvanced Tab) of the sedimentation basin, pond , or 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.

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Image AddedOrifice 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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