The portion of a river's discharge that is supplied by groundwater seeping into the bed is called baseflow.

• A. Discharge
• B. Baseflow
• C. Phreatic zone
• D. Hortonian flow

Answer: (B)

In river hydrology, baseflow is the portion of discharge that comes from groundwater seeping into the bed and banks of the stream. This groundwater contribution keeps the river flowing during dry periods and forms the sustained, low-flow component of the stream.

Discharge refers to the total flow in the river, which includes both baseflow and any quick-flow that arrives as runoff after rain. The phreatic zone is the underground region where the soil and rock are saturated with water, not the act of discharge itself. Hortonian flow describes rainfall-driven surface runoff that occurs when rainfall exceeds the soil’s infiltration capacity, not the groundwater-fed portion of flow.

So the best answer is baseflow because it specifically denotes the groundwater-supplied component that maintains river discharge between rain events.