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.
A conceptual diagram of the pond, detention basin and sedimentation basin properties in MUSIC is presented below:
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All of the stormwater that approaches the pond below the user-defined Low Flow Bypass amount (in units of m3/s) will bypass the pond. Any flow above the Low Flow Bypass (subject to the presence of a High Flow Bypass) will enter and be treated by the pond.
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When the stormwater inflow rate exceeds the user-defined High Flow Bypass amount (in units of m3/s), only a flow rate equal to the High Flow Bypass (less that specified in any Low Flow Bypass) will enter and be treated by the pond. All of the stormwater flow in excess of the High Flow Bypass amount will bypass the pond and will not be treated.
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The Low and High Flow Bypasses are assumed to occur simultaneously. So for a Low Flow Bypass of 2m3/s, a High Flow Bypass of 8m3/s, and inflow of 10m3/s:
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Storage Properties
The Storage Properties define the physical characteristics of the main pond, detention basin or sedimentation basin.
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Defines the surface area of the pond, detention basin or sedimentation basin in m2. The hydrologic routing analysis calculates the volume of water in storage during a storm event by multiplying the depth of water above the permanent pool in the pond or sedimentation basin by this surface area.
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Defines the depth of water above the permanent pool that must be reached in the pond, detention basin or sedimentation basin before flow starts to discharge over the outflow weir. The Extended Detention Depth is defined as a depth in metres.
Permanent Pool Volume
The pond, detention basin or sedimentation basin has a permanent volume of water which does not affect the hydrologic routing of a storm event through the system. However, this permanent pool does affect the hydraulic detention time during a storm event, and so affects the treatment of contaminants that flow into the pond, detention basin or sedimentation basin. The Permanent Pool Volume is defined in m3 and is available for stormwater reuse abstraction.
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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.
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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.
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The button 
allows you to estimate the surface area of the sedimentation basin. Clicking it opens the Estimate
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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 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 sedimentation 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.
Custom Storage-Discharge-Height Relationship
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.
This button opens the Estimate Storage Properties dialogue box:
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Estimate Parameters
There is an option to set up the parameters in Sedimentation Basin as shown in figure below:
Clicking will open the Estimate Parameters dialog box as below:
The parameters are the same as those for wetlands (refer to this page), with one exception:
Permanent Pool Volume
This value is calculated based on two parameters that were specified in the Properties for Sedimentation dialogue box - Permanent Pool Depth and Initial Surface Area.
Re-use
There is an option to re-use water from the Sedimentation Basin, by specifying a demand. The parameters are the same as those for wetlands (refer to this page), with one exception:
Permanent Pool Volume
This value is calculated based on two parameters that were specified in the Properties for Sedimentation dialogue box - Permanent Pool Depth and Initial Surface Area.
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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.
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You can use the node water balance report to obtain basic information on the overall water balance at the pond, detention basin or sediment basinthese nodes, including basic information on reuse at the node. To do this, select node water balance from the list of available reporting boxes by right clicking on 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 pond, detention basin or sediment the sedimentation basin as shown below.
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button can also be used to save data on the water re-use demand and supply at every time-step should that be required (see below).
It is possible to record flux data 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.
Refer to Fluxes for more information about fluxes.
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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.
Orifice Discharge Coefficient
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The overflow weir carries a discharge when the water level in the pond or sedimentatin 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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Tip Box
Where a permanent pool is present, only a single background concentration C* applies. The parameters for C** and Threshold Hydraulic Loading will only be enabled when the permanent pool volume is set to zero.
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NOTE: Advanced Properties are uneditable by default. You can make it editable for each project by clicking on Edit and Project Options. This will present you with a Project Options Screen as displayed below:
Now, click on MUSICX Treatment Node Settings and tick on Editable as shown above. |
