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- Created by Abraham Toribio, last modified on Jul 01, 2018

**Bioretention stormwater controls** may be referred to, among other names, as biofiltration basins, bio basins, biofilters or a raingardens.

Bio swales or biofiltration swales can also be modeled as Bioretention stormwater controls.

Note - Only the desired facility criteria must be populated; for example - for only flow routing simulation the Dimension tabs must be populated, while the rest of the facility description tabs can be left blank.

**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.

**Ponding Area:**

The depth within the ponding area is determined from two of the following three parameters, with the third automatically calculated based on the option selected:

- Represents the level (above datum) of the stormwater control above which flooding is reported. This may be the level that interacts with the ground surface or the top of an embankment, whichever is higher. An overflow or spillway crest level may be specified at a lower level as part of the outlet control details. If a Surface Data model (TIN) is present the Exceedence Level will automatically be picked up from the centre of the icon or from the lowest point on the bioretention perimeter if an outline has been drawn. This combined with the Freeboard setting allows a Status of Flood Risk to be assigned to the system on the Summary. For stormwater controls on a slope the Exceedence level applies to the downstream (lowest) end. Above the Exceedence Level, water will be stored above the ground and then allowed to drain back into the network. The default ponding area used for the flooded volume is 1000m² .**Exceedence Level**Represents the depth of the ponding area.**Depth**-- Represents the level (above datum) of the base of the ponding area (or top of the filter area). For structures on a slope the invert level applies to the downstream (lowest) end.**Base Level**

The cross sectional area of the ponding area is then determined from the Top Area, Side Slope and Base Area. As per the depth calculation when two values are specified the third will automatically be calculated based on the option selected:

- Displays the calculated surface area at the Top of the ponding area.**Top Area**Side Slope of the ponding area.**Side Slope**-Defines the surface area at the base of the ponding area. This also gives the plan area of the filter of the bioretention system.**Base Area**-

Note: Behind the scenes the length is used along with the top and base areas to determine the cross section. if no length is specified the software has to assume the structure is circular.

* 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.

**Filter Area:**

* Base Level* - Represents the level (above datum) of the base of the bioretention stormwater control. Automatically populated by subtracting the Ponding Depth and the Filter Depth from the Exceedence Level.

* Under Drain:* Specifies whether a pipe or conduit underdrain 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 stormwater control.

* 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.

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The Sizing Calculator option allows the user to re-size the Bioretention 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.

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* Filtration Layer Name* - Allows the user to enter a name for each filtration layer.

* Filtration Depth* - Depth of the filter layer.

* Void Ratio *- Void Ratio of the filter layer; e.g. a value of 30.000 represents 30% void space.

* Filtration Rate* - Defines the rate of flow through the filter medium based on the material used. May be referred to as saturated hydraulic conductivity.

*Note*: The rate at which water moves from the ponding area into the filter area is determined by the top filter layers Filtration rate.

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.

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**Ponding Area:**

* Side Infiltration Rate* - Defines the rate of infiltration through the sides of the ponding area. This should be determined from a performance site test.

* Base Perimeter* - Defines the perimeter of the ponding area at the base of the ponding area. If the surface area is drawn on the Plan the field will be automatically populated based on the side slope and the Top Perimeter. It can also be overwritten to become user-defined.

* Top Perimeter *- Defines the perimeter of the ponding area at the top of the ponding area (exceedence level). If the surface area is drawn on the Plan the field will be automatically populated but can be overwritten to become user-defined.

* Interception Volume* - For the combined ponding and filter area, this represents 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* - For combined ponding and filter area. 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/Junctionsmethod to calculate velocity, flow and volume for each timestep.The value can be calculated based on the dimensions of the stormwater control in several ways:

**Manning's equation**- The software can determine the retention time based on the dimensions will be used to determine the travel time using the Manning Formula equation. To do this a Manning's n value must first be specified on the calculator. The calculated velocity will then be applied to the Length of the system to determine the retention time.**Colebrook-White equation**- The software can determine the retention time based on the dimensions will be used to determine the travel time using the Colebrook-White Formula equation. To do this a Colebrook-White roughness value must first be specified on the calculator. The calculated velocity will then be applied to the Length of the system to determine the retention time.**User Specified**- If the retention time is a know value it can simply be entered into the field to bypass any calculations.

* Retention Coefficient* - Analysis of SWC/Junctions attenuation coefficient for the ponding area – 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.

**Filter Area:**

* 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.

* 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 stormwater control in several ways:

**Under Drain**- If the Under Drain is being used, its dimensions will be used to determine the travel time using either the Manning's equation or the Colebrook-White equation.**Hydraulic Conductivity**- Without the under drain the software can determine the retention time based on the filter rate within the system. This will be determine automatically from the filter table or alternatively a value can be entered on the calculator. This will then be applied to the Length of the system to determine the retention time.**User Specified**- If the retention time is a know value it can simply be entered into the field to bypass any calculations.

* 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:

**Hydraulic Conductivity**- The software can determine the retention time based on the filter rate within the system. This will be determine automatically from the filter table or alternatively a value can be entered on the calculator. This will then be applied to the depth of the filter to determine the retention time.**User Specified**- If the retention time is a know value it can simply be entered into the field to bypass any calculations.

* Retention Coefficient* - Analysis of SWC/Junctions attenuation coefficient for the filter area – 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.

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** 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 Filter or Ponding Pollution.

* 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__

- Bioretention
- Chamber
- Infiltration Trench
- Pond
- Porous Paving
- Soakaway
- Swale
- Tank
- User Defined
- Stormwater Control Sizing Calculator

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** Bioretention** on these objects then choose to connect to another Junction or Stormwater Control.