How do aquifers contribute to baseflow during dry periods?

• A. Aquifers store water but do not discharge to streams.
• B. Aquifers increase surface runoff.
• C. Groundwater in aquifers slowly discharges to streams, maintaining baseflow when rainfall is low.
• D. Aquifers only store water and cause flooding.

Answer: (C)

The main idea is that groundwater stored in aquifers feeds streams during dry periods, keeping baseflow steady. When rainfall wanes, water has already infiltrated and recharged the aquifer, and it moves slowly through the soil and rock. This slow groundwater discharge into the stream—often where the aquifer intersects the riverbed or along the banks—adds a constant, low-intensity flow that maintains stream levels between rain events. This is baseflow: the part of streamflow supplied by groundwater rather than direct rainfall runoff.

So, aquifers contribute by acting as a reservoir that releases water gradually to streams when surface input is low, rather than increasing surface runoff or solely storing water to cause flooding.