Swale stormwater controls may be used to model a range of stormwater controls including, but not limited to, wet swales, vegetated, dry swales, French drains, filter trenches, infiltration trenches, trench soakaways, wadis, all with and without under drain pipes.
Total Volume
The Total Volume value shown in the bottom-right corner of the data form shows the volume available in the system up to the Freeboard level.
The depth within the Swale area is determined from two of the following three parameters, with the third automatically calculated based on the option selected:
The cross sectional area of the Swale area is then determined from the Top Width, Side Slope and Base Width. As per the depth calculation when two values are specified the third will automatically be calculated based on the option selected:
Freeboard - Controls how close to the specified Exceedence Level the water must reach before the Status (on the Summary) shows Flood Risk.
Length - The maximum path length through the stormwater control, used only for the purpose of calculating Time of Travel. The Length will be automatically set from the dimensions of the stormwater control unless over typed, in which case it is set to "user specified".
Longitudinal Slope - Slope along the length of the stormwater control.
Filtration Rate - Defines the filtration rate from the Swale into the Trench if used.
Trench:
Trench Depth - The depth of the trench
Trench Void Ratio - The percentage of the trench that is available for storage. This is dictated by the type of fill material that is used. I.e. Typically 30% for rubble.
Under Drain: Specifies whether a pipe or conduit under drain is present in the lowest layer of the filter area. If under drain is on the following can be specified:
Height Above Base - Height of the invert of the pipe above the base of the bioretention system.
Diameter - Defines the diameter of the pipe/s.
No of Barrels - Represents the number of pipes.
Velocity Calculation Type - Specifies the formula used to calculate velocity and time of travel. Select from: Manning's, and Colebrook-White. The variable below the combo box depends on the Velocity Calculation Type selected.
n - Manning’s n roughness value. Used by the Manning Formula equation to calculate the velocity and therefore time of travel when using the Manning's Velocity Calculation Type.
Roughness - Colebrook-White roughness value. Used by the Colebrook-White Formula equation to calculate the velocity and therefore time of travel when using the Colebrook-White Velocity Calculation Type.
Release Height - Height above the invert of the under drain pipe at which the water is released (marked in red on the diagram below). This is commonly used to create a saturated zone.
The Sizing Calculator option allows the user to re-size the Swale by specifying a volume and a parameter to modify to achieve that volume. The Sizing Calculator is discussed in more detail in the Stormwater Control Sizing Calculator section.
Explore the Inlets page for more details on the different types of Inlets that can be specified.
Explore the Outlets page for more details on the different types of Outlets that can be specified.
Swale:
Base infiltration rate - Defines the rate of infiltration through the base of the filter area. This should be determined from a performance site test.
Side infiltration rate - Defines the rate of infiltration through the sides of the filter area. This should be determined from a performance site test.
Void Ratio - The percentage of the swale that is available for storage. This is dictated by the type of fill material that is used. I.e. 100% if empty or typically 30% for rubble.
Interception Volume - For the combined ponding and filter area. The volume of water that enters the stormwater control that is permanently held within it. Once full it can be emptied by evapotranspiration only.
Evapotranspiration - The amount of water lost to the environment due to evaporation, transpiration and evapotranspiration. Used by the software during analysis. First the evapotranspiration removes water held in the swale, then it removes water from the interception storage volume.
Horizontal Retention - Specifies the time for water to pass from the inlet to the outlet in the horizontal direction. This is used in the Analysis of SWC/Junctions method to calculate velocity, flow and volume for each timestep.The value can be calculated based on the dimensions of the system in several ways:
Retention Coefficient - Analysis of SWC/Junctions attenuation coefficient for the swale – scalar value between 0.1 and 0.5. This will be calculated automatically from the dimensions of the system using Muskingum-Cunge. Alternatively the value can be entered by the user if known to bypass any calculations.
Trench:
Base infiltration rate - Defines the rate of infiltration through the base of the filter area. This should be determined from a performance site test.
Side infiltration rate - Defines the rate of infiltration through the sides of the filter area. This should be determined from a performance site test.
Interception Volume - The volume of water that enters the stormwater control that is permanently held within it. Once full it can be emptied by evapotranspiration only.
Evapotranspiration - The amount of water lost to the environment due to evaporation, transpiration and evapotranspiration. Used by the software during analysis. First the evapotranspiration removes water held in the swale, then it removes water from the interception storage volume. Note: This is only available if the Swale is turned off.
Horizontal Retention - Specifies the time for water to pass from the inlet to the outlet in the horizontal direction. This is used in the Muskingum method to calculate velocity, flow and volume for each timestep.The value can be calculated based on the dimensions of the system in several ways:
Vertical Retention - Specifies the time for water to pass from the inlet to the outlet in the vertical direction. This is used in the Analysis of SWC/Junctions method to calculate velocity, flow and volume for each timestep. The value can be calculated based on the dimensions of the system in several ways:
Retention Coefficient - Analysis of SWC/Junctions attenuation coefficient for the trench – scalar value between 0.1 and 0.5. This will be calculated automatically from the dimensions of the system using Muskingum-Cunge. Alternatively the value can be entered by the user if known to bypass any calculations.
Name - Name of pollutants. This is populated based on the Pollutants set up as part of the Site Data.
Aspect - A section that details if the pollutant is Swale or Trench.
Concentration - Value below which the pollution concentration cannot fall during analysis. When concentration reaches this level, no further removal occurs.
Method - Percentage Removal or First Order Decay method can be chosen. Click on the links for more information about each method.
Percentage Removal - Available if Percentage Removal entered. The value entered will be deducted from the Inflow into the system.
τ - The decay time constant or (mean) lifetime of the pollutant. It can be entered manually or calculated from the decay constant or decay half-life. See Pollutant Removal Method - First Order Decay for more details.
Section Pages
These systems can be customized to represent a variety of drainage or treatment facilities. Please review the description of each system to see which one would be the most convenient to use.
Workflow - What's next...?
Inflows connect to either Junctions or Stormwater controls via Inlets . Specify an Swale on these objects then choose to connect to another Junction or Stormwater Control.