HydroCAD® Stormwater Modeling - Since 1986
Stormwater Storage Chambers
These products provide an alternative to traditional above-ground storage and maximize land utilization while increasing infiltration and groundwater recharge.
Starting with HydroCAD-9.0, the interactive chamber wizard greatly simplifies the layout, pricing, and modeling of underground storage systems. HydroCAD-10 expands these capabilities with automatic handling of end caps, special start-end chambers, and pipe headers.
Storage Chamber Definitions
Support for prefabricated chambers is provided by a library of common chambers, which is automatically installed in the "Chambers" folder. Storage data can be viewed in tabular or graphical format, as show in the graph above from the View|Chamber screen.
Note that chamber definitions are required only for specialized (curved) storage volumes that cannot be modeled by one of the standard storage options. For example, any kind of rectangular storage can be modeled using the "prismatoid" option, and pipes can be modeled with the "horizontal cylinder" or "pipe storage" option. However, chamber definitions are also useful for "regular" shapes, since they facilitate comparison of different storage options (as shown in the screen shot above), and can be used with the underground storage wizard.
Please contact us if you need support for a storage product that is not listed above. If necessary, custom chamber definitions can be created with the built-in chamber file editor as described here.
Embedded Storage Calculations
Specialized ponds, such as a hollow chamber in a bed of crushed stone, can be modeled by embedding one storage definition within another. This allows HydroCAD to automatically calculate the effective storage of the overall structure at any required elevation.
The "Embed Inside" box on each storage screen controls the Embedding process. This box is normally set to "Nothing", in order to define multiple non-overlapping storage areas. Other selections may be used to configure embedded chambers, as described in the following example.
Allowing for Wall Thickness
If an embedded volume has a significant wall thickness, the displaced volume will be somewhat greater than the internal storage. To allow for this difference, HydroCAD 8.5 (and later) allows a wall thickness to be specified for most common storage definitions, or included within a chamber definition file. This allows automatic calculation of displaced volume for thick-walled storage volumes, such as concrete pipes and leaching chambers.
Automated Modeling Instructions
The underground storage wizard (added in HydroCAD-9.0) eliminates the multiple steps that were previously required for chamber modeling. Just pick the chamber and set the layout parameters, and HydroCAD builds the complete storage model. The wizard can automatically apply the manufacturer's recommended chamber spacing, bedding, and cover, or you can set these values manually. For HydroCAD 8.5 and earlier, please see the manual procedure.
For additional details please see the chamber tutorial, which is also included in HydroCAD help.
Completing the Model
After using the chamber wizard, you can define any additional storage volumes, such as above-grade ponding or the storage of connected manifolds or catch basins. You can also define any overflow devices used to handle excess volume when the chambers fill up. If the model indicates an overflow condition, you must define these elements in order get meaningful results. Details here.
If you want to model exfiltration, create an exfiltration outlet on the pond. This will let you enter the velocity at which the water will leave the outermost storage volume (the excavation) as it enters the surrounding soil. Since the exfiltration is automatically calculated based on the outer area, you do not need to change the discharge multiplier to reflect the number of chambers, so leave the default multiplier of 1.
Your chamber system may also have additional outlet devices, such as an overflow weir or low-flow orifice, which can help to maximize the utilization of chamber volume. "Offline storage" arrangements are also common, as discussed here.
After setting up all the storage definitions and outlet devices, review the pond summary report to see the final storage calculations. Examine the report carefully to be sure everything is set up as intended.
For More Information
Please see the following pages for further information:
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