HydroCAD Stormwater Modeling - Since 1986

Manual Chamber Modeling

This page discusses the manual procedure for modeling stormwater chambers in HydroCAD.  However, users of HydroCAD 9.0 or later will generally prefer to use the new chamber wizard, which performs most of these steps automatically.

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%.

Click for complete self-training materialsWhen 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) Additional storage definitions, exfiltration, and other outlet devices can be added as discussed here.

For further details see the chamber tutorial.

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