LID Representation
LID controls are represented by a combination of vertical layers whose properties are defined on a per-unit-area basis. This allows LIDs of the same design but differing areal coverage to easily be placed within different subcatchments in a study area.
During a simulation, GeoSWMM performs a moisture balance that keeps track of how much water moves between and is stored within each LID layer. As an example, the layers used to model a bio-retention cell and the flow pathways between them are shown below:
Fig.52: A bio-retention cell (Source: User Manual for EPA-SWMM 5.1)
The following table indicates which combination of layers applies to each type of LID (x means required, o means optional):
| LID Type | Surface | Pavement | Soil | Storage | Drain | Drainage Mat |
|---|---|---|---|---|---|---|
| Bio-retention Cell | x | x | x | o | ||
| Rain Garden | x | x | ||||
| Green Roof | x | x | x | |||
| Infiltration Trench | x | x | o | |||
| Permeable Pavement | x | x | o | x | o | |
| Rain Barrel | x | x | x | |||
| Rooftop Disconnection | x | x | ||||
| Vegetative Swale | x |
When a user adds a specific type of LID control object to a GeoSWMM project the LID Control Editor is used to set the design properties of each relevant layer (such as thickness, void volume, hydraulic conductivity, drain characteristics, etc.). These LID objects can then be placed within selected subcatchments at any desired sizing (or areal coverage) by editing the subcatchment’s LID Controls property.