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.
This spreadsheet specifies the circular infiltration cross-sectional area and volume for the structure at each depth. A depth of 0m corresponds to the invert level and area specified at 0m is considered to be the base of the structure. All areas above the top of the structure may be left as blank.
Above the spreadsheet is an Editable Column drop-down list box which allows the user to specify either 'Area' or 'Volume' values in the spreadsheet.
Whilst the Area at each depth specifies the circular cross-sectional area at that depth, the volume is the cumulative volume for all depths up to the depth the next row. If the Editable Column drop-down list box is 'Area' then the user can specify an area and the volume in the same row is calculated calculated. Conversely if 'Volume' is selected in the Editable Column drop-down list box then the user can specify a volume in a row and the area is calculated in the subsequent row (keeping the area in the same row the same). Note that in this case it is possible to specify a volume that is it too small for the area of the current row and height between the current and next rows, in which case the area will be set to -1 and a higher volume will need to be 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.
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.
Perimeter - Specified whether the perimeter shape for the side infiltration calculation is to be circular or square. The default is circular.
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 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.
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.
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...?