Bentley StormCAD CONNECT can calculate the accumulation, re-distribution, and melting of precipitation that falls as snow on a catchment. In addition, Bentley StormCAD CONNECT can model groundwater flow between and aquifer underneath a catchment and a node of the drainage system.

The snowmelt and groundwater calculations both require the catchment's Runoff Method to be set to 'EPA-SWMM Runoff', and the Engine Type to be set to 'Explicit (SWMM 5)' in the calculation options. For methods to determine snowmelt rates, the user is referred to the Haestad Press publication "Stormwater Conveyance Modeling and Design".

Shown below is a definitional sketch of the two-zone groundwater model that is used in SWMM. The upper zone is unsaturated with a variable moisture content of θ. The lower zone is fully saturated and therefore its moisture content is fixed at the soil porosity ϕ.

The fluxes shown in the figure, expressed as volume per unit area per unit time, consist of the following:

After computing the water fluxes that exist during a given time step, a mass balance is written for the change in water volume stored in each zone so that a new water table depth and unsaturated zone moisture content can be computed for the next time step.

See also:

• "SWMM Hydrology"
• "SWMM Snow Packs (SWMM Snow Pack Editor)"
• "Climatology Dialog Box"