Tank stormwater controls may be used to model a range of stormwater controls including, but not limited to, tanks and municipal harvesting tanks.
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 stormwater control is determined from two of the following three parameters, with the third automatically 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.
Initial Depth - Defines the initial wetted depth within the facility.
Void Ratio - Defines the percentage of the tank 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.
Enter the plan area and infiltration area of the stormwater control at each depth. A depth of 0m corresponds to the invert level. All areas above the top of the structure may be left as 0.
The infiltration area specified at 0m is considered to be the base of the structure. The side surface at a given depth is the infiltration area specified for that depth less the base area.
The circular button will calculate the infiltration surface automatically based on a circular shape and the areas specified.
Depth Increment (m)
Enter the depth increment for the tank area spreadsheet. Small values lead to a more accurate result but limit the height of the structure.
The Sizing Calculator option allows the user to re-size the Tank by specifying a volume and a parameter to modify to achieve that volume. It also allows the user to specify a Side Slope for the Tank. 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.
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. Note: this cannot be emptied as there is no evapotranspiration for tanks.
Routing Method - provides three ways of determining the time it takes to water to travel through the system:
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 – scalar value between 0.1 and 0.5. This will be calculated automatically from the dimensions of the system using Musikingum-Cunge. Alternatively the value can be entered by the user if known to bypass any calculations.
Pollution Name - Name of pollutants. This is populated based on the Pollutants set up as part of the Site Data.
Background Concentration - Value below which the pollution concentration cannot fall during analysis. When concentration reaches this level, no further removal occurs.
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.
Stormwater Control Types
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...?