Baseflow

Baseflow (also called drought flow, groundwater recession flow, low flow, low-water flow, low-water discharge and sustained or fair-weather runoff) is the portion of streamflow that comes from "the sum of deep subsurface flow and delayed shallow subsurface flow". It should not be confused with groundwater flow.Fair weather flow is called as Base flow.

Certain parameters of baseflow, such as the mean residence time and the baseflow recession curve, can be useful in describing the mixing of waters (such as from precipitation and groundwater) and the level of groundwater contribution to streamflow in catchments.

Baseflow separation is often used to determine what portion of a streamflow hydrograph occurs from baseflow, and what portion occurs from overland flow. Common methods include using isotope tracing and the software program HYSEP, among others.

...
Wikipedia