Soakaway pits are excavations in the ground filled with clean granular stone or other void forming material that receives “clean” runoff designed to infiltrate into the native soil. Soakaway pits are designed with an overflow and an optional subdrain feature. Key features for Soakaway pit designs are highlighted in the diagram below.


Parameter Name Description Default Value
Storage Layer
POROSITY Fraction of void space (pores) in the gravel storage layer 0.4
Initial Water Level Depth of water in the storage layer at the start of a model run 0

Interpreting Soakawaypit output:

In the following figure, you can see a sample of soakawaypit output:

“IN” and “OUT” means the inflow and outflow for the soakwaypit.
“Length”, “Height”, “Porosity”, “Initial Water Level”, “Width”, and “Min. Drawdown” are the properties defined by the user.
“Max. Drawdown” presents the maximum time of drawdown. Note: Texture and infiltration of the native soil affect the drawdown time.
The table presents information about the inflow and outflow of the soakawaypite.
“Volume Reduction Rate[(RVin-RVout)/RVin](%)” shows the effect of the soakawaypit on the runoff. Then, you can see the time to reach the maximum storage, how much water exists, and how much is the drawdown time.