Vegetated swales are open channel systems which utilise vegetation to aid removal of suspended solids. As for buffer strips, the vegetation can assist in reducing peak flows for a range of events (dependent on the swale width and length) and may also be beneficial in volumetric reduction through infiltration, dependent upon the underlying soil conditions. These systems are subjected to fairly high hydraulic loading and the removal efficiency is dependent on the density and height of the vegetation in the channel.
A conceptual diagram of the swale properties in MUSIC is presented below:
Conceptual diagram of swale properties.
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Flow in a vegetated swale is modelled in the USTM as uniform flow in a trapezoidal channel (although a triangular channel can be simulated by setting the base width to 0m).
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Inlet Properties
Low Flow Bypass
All of the stormwater that approaches the swale below the user-defined Low Flow Bypass amount (in units of m3/s) will bypass the swale. Any flow above the Low Flow Bypass (up to the defined capacity of the swale) will enter and be treated by the swale.
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Storage Properties
The storage properties describe the physical characteristics of the vegetated swale and are used to determine the water depth versus discharge relationship, which is used in the hydrologic routing of stormwater runoff through the swale.
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The Manning’s n roughness of the vegetated channel is determined from the vegetation height, based on work described by Kouwen (1988), Kouwen and Li (1980) and Kouwen and Unny (1973). A more detailed discussion of the algorithm is given in Calculating Manning's n in Swales.
Batter Slope
Slope of the side of the channel. Note that this must not be confused with the slope of the actual channel.
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This is also known as high flow bypass. music calculates the capacity of the swale for the given dimensions and vegetation. Inflow in excess of the calculated capacity is treated as a high flow bypass.
It is possible to record flux data It is possible to view or save various flows and water quality as below for the swale:
- inflow rate and water quality
- outflow rate and water quality
- low flow bypass and water quality
- overflow rate and water quality
- total outflow rate (sum of outflow, bypass flows and overflow) and water quality
- computed water levels and storage.
Refer to Fluxes for more information about fluxes.
The Notes button allows you to record any important details or assumptions for the swale (for example, you may provide an explanation of how the vegetation height was estimated). It is good practice to provide notes of any important assumptions, for future reference by others using the model.You need to select them to record before you run.
Advanced Swale Properties
The advanced properties section (opened using the ‘More’ button) of the swale properties dialogue box displays the parameters that describe the treatment processes in the swale as shown below.
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For details on configuring CSTR cells, refer to Number of CSTR Cells. An infinite number of CSTRs would replicate the effects of plug flow through the swale. music defaults to 10 CSTR cells for swales as most swales are relatively long and thin, however, as the shape of the system can vary markedly dependent on design, the number of CSTR cells that is required to represent the hydraulic efficiency of the design is dependent on that shape.
For swales:
- k and C* - The rate at which each contaminant is treated, and the background concentration for each contaminant will be different within a vegetated swale and different values should be adopted for each contaminant.
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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. |
