Problem

What is the purpose of the "Percent Void Space" column in the properties of a pond's elevation-area or elevation-volume curve?

Solution

The "percent void space" is used to adjust your pond's storage volume for things like rock fill. For example if you know the pond's volume before rock fill is added, you can enter that, and then adjust for the rock fill using the percent void space.

In the pond properties, open the Elevation-area or elevation-volume curve (assuming your pond is using one of these methods) by clicking the ellipsis button:

Here you will see the area (or volume) values along with the percent void space which you can adjust or global edit as needed.

Troubleshooting

The following User Notification is seen after computing: "The SWMM engine does not support Void Space values other than 100 percent, alternate values are ignored."

This is an informational message, but you may want to take action if you were trying to adjust your pond volume with a void space less than 100%. The message is telling you that the Explicit (SWMM) solver (selected in the calculation options) does not support this option and instead assumes the entire entered pond volume is available for storage, which can impact the results if you actually have some fill to account for. In this case you would need to manually adjust the elevation-volume or elevation-area curve to compensate for this.

See Also

Pond and pond outlet assumptions in StormCAD, SewerGEMS, CivilStorm and SewerCAD