Ponds can lose water by seepage (infiltration/exfiltration into the groundwater) or by evaporation. Any water lost by seepage or evaporation does not show up in downstream links and the flow is considered as lost from the system.

No flow loss is the default set ("None" as default loss method).

Depending on the numerical solver used, following loss methods are supported:

Implicit (DW) and GVF-Convex solvers:

• Constant Seepage Loss: A Constant Flow rate given in flow units.
• Average Seepage Loss: An Average Infiltration rate in depth per unit time which is multiplied by the area of the pond surface at that time step to determine the infiltration rate.
• No evaporation is supported.

In applying either method, the models also has a stability filter when the pond water depth is below 0.5 ft so that the seepage loss rate will linearly reduce to zero as the depth decreases to zero.

Explicit (SWMM) solver:

• Green-Ampt: The Green- Ampt infiltration method is used to compute the pond seepage loss, in which suction head, conductivity and initial deficit data are required.
• Evaporation loss is supported, a few evaporation types can be defined in the climatology data (under Components - SWMM Extensions) and a user specified evaporation factor for the pond.