Interflow Reservoirs

The interflow reservoirs are used to route near-surface groundwater to local streams. In the Linear Reservoir Method, each reservoir is assumed to be like a bathtub, with an inflow from infiltration and the upstream reservoir, as well as an outflow flowing into the next downstream reservoir and down into the baseflow reservoir beneath. Each linear reservoir flows only into the next downstream interflow reservoir, or into a stream if it is the lowest reservoir.

Note Polygon shape files are currently not allowed for defining interflow reservoirs. The flow reference between interflow reservoirs depends precisely on the integer code numbers assigned to the reservoirs. Within a subcatchment, the interflow reservoir with the higher number always flows into the reservoir with the next lowest number.

Each Interflow reservoir requires a value for:

Specific Yield - to account for the fact that the reservoir contains a porous media, and is not an actual bathtub.

Initial depth - the initial depth of water in the reservoir, measured from the ground surface.

Bottom depth - the depth below the ground surface of the bottom of the reservoir. If the water level drops to the bottom of the reservoir, percolation stops.

Interflow time constant - a calibration parameter that represents the time it takes for water to flow through the reservoir to the next reservoir.

Percolation time constant - a calibration parameter that represents the time it takes for water to seep down into the baseflow reservoir

Interflow threshold depth - the depth below the ground surface when interflow stops. If interflow stops, percolation will continue until the reservoir is empty (i.e the water level reaches the bottom depth). The threshold depth must be less than or equal to the depth to the bottom of the reservoir.