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The initial wetland properties dialogue box contains the parameters that describe the basic physical characteristics of the wetland system:
Inlet Properties
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A custom pipe flow, weir flow and storage relationship can be specified to represent custom outlet and storage configurations for wetland nodes. 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 here.
Estimate Inlet Volume
There is an option to set up the initial pond volume of the wetland as shown in figure below:
Clicking will open the Estimate Inlet Volume opens the dialog box as below:
Input Parameters
This defines the input parameters of the inlet.
Particle size
The average diameter of the targeted sediments. Units are in microns (1e-6m).
Settling velocity
Velocity of the particle when settling, during the sedimentation process. In other words, the velocity of the particle into water under gravity and Archimedes constraints.
Contributing Catchment Area
Area of the catchment contributing to pollutant generation.
Design Flow
The ideal flow that can be handled by the wetland.
Sediment Loading Rate
Volume of sediments expected to be received (in ha/yr).
Capture Efficiency
The proportion of total volume entering the basin that is targeted to settle.
Clean Out Frequency
The frequency of wetland maintenance (in years). In other words, how often is the basin emptied and cleaned out.
Turbulence
This is the number of CSTR cells.
Detention Depth
The depth from the top of the permanent pool to the top of the overflow weir. The inlet pond of a wetland has a detention depth of 0.
Estimates
The required area (A) of a sedimentation basin should be defined using the equation shown below:
where
R fraction of target sediment removed
Vs settling velocity of target sediment (see the table below)
Q/A applied flow rate divided by basin surface area
n turbulence or short-circuiting parameter
de extended detention depth (m) above permanent pool level
dp depth (m) of the permanent pool
d* depth below the permanent pool level that is sufficient to retain the target sediment (m) - adopt 1.0m or dp, which is lower
The table below lists the typical settling velocities (Vs) of sediments under 'ideal conditions' (velocity in standing water)
(Source: Maryland Dept. of Environment 1987 in Engineers Australia 2003)
Classification of particle size | Particle diameter (µm) | Settling velocities (mm/s) |
Very coarse sand | 2000 | 200 |
Coarse sand | 1000 | 100 |
Medium sand | 500 | 53 |
Fine sand | 250 | 26 |
Very fine sand | 125 | 11 |
Coarse silt | 62 | 2.3 |
Medium silt | 31 | 0.66 |
Fine silt | 16 | 0.18 |
Very fine silt | 8 | 0.04 |
Clay | 4 | 0.011 |
Surface Area Requirement
Surface area required by the previously fixed depth.
Sediment Storage Volume Requirement
Volume requirement according to sediment loading (which is the efficiency load*flow*contributing area).
Permanent Pool Volume Requirement
Twice the sediment storage volume.
Re-use
There is an option to re-use water from the wetland, by specifying a demand. Refer to Water Re-use from Treatment Nodes for more information about the Re-use tab.
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