Stormwater Storage Chambers
HydroCAD provides built-in support for a wide range of prefabricated stormwater storage chambers, including:
Plastic arch chambers: CULTEC, StormTech, LandSaver, Triton Stormwater, CONTECH
Modular plastic chambers: Brentwood Industries, Atlantis, Invisible Structures, Hydro International, Cudo, ecoChamber, DeepRoot Silva Cell
Concrete chambers: CONTECH, NEPCA, Terre-Hill
HDPE Pipe Storage: ADS N-12®
Corrugated Metal Pipe Storage (standard sizes of round & arch CMP)
Reinforced Concrete Pipe (standard sizes of round, arch, elliptical, box & crown-span)
Custom solutions: GeoStorage
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.
If you need to model a chamber that is not included in your current HydroCAD program, click here for details on free chamber updates.
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.
Detailed Modeling Instructions
Automated Procedure (for HydroCAD 9.0 and later)
The underground storage wizard 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.
After running the chamber wizard, you can define additional storage, exfiltration, or outlet devices as described in the manual procedure, below.
Manual Procedure (for HydroCAD 8.5 and earlier)
1) First define the outer storage area (volume#1) that will enclose all the embedded chambers. You may use any of the standard storage options, without any manual adjustments for the embedded chambers. Set the voids based on the backfill material, such as 40% for crushed stone.
Note: In order to correctly calculate the exfiltration area, you should specify the overall dimensions of the entire storage area. Using the stone dimensions around one chamber (with a storage multiplier) will not give the correct sidewall area required for certain exfiltration calculations!
2) After defining the outer storage volume, define each of the embedded chambers. On each storage screen, use the "Embed Inside" box to select the outer storage volume in which you wish to embed the chamber. (In this example, you would select volume #1.) Since the embedded chamber usually contains no backfill, leave the voids at 100%.
When
embedding several identical chambers, you can use the Storage Multiplier to
specify the number of chambers. Otherwise, repeat step 2 as required for each
embedded chamber.
3) If the chambers are being placed on a bed of material that differs from the rest of the backfill, this can be entered as an additional storage definition embedded within the outer storage area. Set the voids for the base material as required.
4) 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.
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 additional details please see the chamber tutorial, which is also included in HydroCAD help.
For More Information
Please see the following pages for further information:
Chamber Modeling
Article (PDF) as
published in
Stormwater Solutions
HydroCAD home page
Pond storage calculations
Exfiltration calculations
General support page
HydroCAD features and capabilities
Free evaluation program
Pricing and ordering