Stormwater Storage Chambers
HydroCAD
provides built-in support for a wide range of prefabricated stormwater
storage chambers, including the complete products lines from CULTEC
and
StormTech. HydroCAD 8.5 also
supports thick-walled chamber definitions, such as concrete
leaching chambers. And a general chamber update is available that adds
support for CONTECH storage products including common CMP
and pipe-arch storage. (Details
below)
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 this graph from the HydroCAD 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 round pipes can be modeled as a "horizontal cylinder". However, chamber definitions do allow easy side-by-side comparisons of different storage options, as shown in the screen shot above.
New Chamber Definitions
A general chamber update is available for HydroCAD 8.5, which adds the following new chamber definitions: (Follow the links for details on specific products.)
CONTECH CON/STORM and CON/SPAN (all sizes)
Corrugated Metal Pipe (CMP) storage (over 30 round and pipe-arch sizes)
Brentwood Industries StormTank (heights from 18" to 36")
Triton Stormwater Solutions (all chamber models)
Other cumulative chamber updates (as listed below)
Click here
to install the chamber update and select the "Run"
option. When you see "HydroCAD Setup" click "Select
Components" to choose the definitions you want to install.
When the installation is complete, start HydroCAD and open the
View|Chamber screen to see the new definitions.
Although the chamber update is available only for HydroCAD 8.5, users of HydroCAD 7+ can download a few individual chamber definitions as listed below. Right-click the desired model and select "Save Target As" to store the file in your HydroCAD\Chambers folder.
CULTEC Recharger-330XL Recharger-150 Recharger-V8 HVLV V8 HVLV F-110
StormTech SC-310, SC-740
LandSaver LS-1633 LS-3052 (same sizes as StormTech models)
HydroLogic Solutions StormChamber
Concrete Galley 8x8x1.5 (requires HydroCAD 8.5 for thick-wall calculations)
After downloading the desired files, the new definitions will automatically appear on the chamber selection lists within HydroCAD. Also try the View|Chamber screen to view and compare the expanded chamber library.
If required, additional chamber definitions can also be created with the built-in chamber file editor as described here. Note that rectangular and circular chambers can be modeled with one of the standard storage shapes, and do not require a custom chamber definition. However, a custom file can be created for convenience and easy comparison with other chambers.
Why are the chamber dimensions different from the manufacturer's data?
The chamber definition files use the effective dimensions of each chamber. These values include the effects of the corrugated sides, and allow exact calculation of the storage volume at any depth. The effective dimensions are generally somewhat less than the overall (outside) dimensions quoted by the manufacturer.
When calculating the volume for multiple chambers in a row, HydroCAD uses the lay-up length, rather than the outside chamber length. This avoids double-counting the volume at the overlap between each successive chamber.
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.
Step-by-step procedure
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.
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 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.
To allow for wall thickness with HydroCAD-8 and earlier, you can specify the outer dimensions of the embedded volume along with the effective voids. For example, if a 36" HDPE pipe has an outside diameter of 41.7", you would enter the outside diameter and set the voids to 75%. (362 / 41.72 = 0.75) This allows the pipe to displace the correct amount of backfill, while providing the expected internal storage.