Exfiltration/Embedded Storage

[jtowne]

I am designing a system with chambers set in a pit on natural earth. I am backfilling 6 inches beyond the chambers with crushed stone. I am modelling the system as a detention pond with a parabolic arch embedded inside a prismatoid. The outlet for the pond/leaching pit is through discarded exfiltration only. The first line on the pond storage tab is a prismatiod. The second line is the parabolic arch and it is shown as inside #1. I am using 40% voids for the prismatoid storage.

My question is what do I use for the length and width on the prismatoid storage screen? If I use the area enclosed by the perimeter of the backfilled crushed stone, I am not getting credit for the open volume (100% voids) in the chambers.

 

[psmart]

You can enter a third storage definition for the volume above the stone. When you define this volume, be sure to remove the check mark from "Allow Exfiltration", otherwise the area of the upper and lower volumes will be added together for the exfiltation calculations.

 

[jtowne]

Thank you PSMART,

The stone is not under the chambers but around the perimeter. The chambers are put in the pit on native soil and then backfilled with stone. I could place a layer of stone under the chambers but for now I just want to understand how to model the backfilled stone which extends 6 inches around the perimeter of the field.

 

[TerryScan]

If one embeds a storage with 100% voids inside of the prismatoid with 40% voids, HydroCad will credit the embedded storage.

Pond 1P: (new Pond)
[43] Hint: Has no inflow (Outflow=Zero)
Routing by Sim-Route method
Peak Elev= 0.00' @ 0.00 hrs Surf.Area= 0.000 ac Storage= 0.000 af
Plug-Flow detention time= (not calculated)
Center-of-Mass det. time= (not calculated)
Volume Invert Avail.Storage Storage Description
#1 50.00' 0.107 af 50.00'W x 100.00'L x 5.00'H Prismatoid
0.574 af Overall - 0.306 af Embedded = 0.268
#2 50.00' 0.306 af 60.0"W x 48.0"H x 5.00'L Parabolic Arch x 2
0.413 af Total Available Storage

 

[psmart]

jtowne,

All you need to do is give the dimmensions of the total volume that will contain the stone and chambers. Set the voids at 40%. This is volume #1 in TerryScan's example.

Then define the chambers as volume #2 and set "embed inside volume #1" Be sure to leave the chamber voids at 100%.

Now check the storage calculations in the pond summary. This will show the exact storage calculation, including the contribution from the stone and chambers.