The Importance Of Snow And Forests To PA Streams And Groundwater

By Bryan Swistock, Penn State Extension Water Resources Coordinator

The forest creates a perfect environment to capture and slowly melt snow into the ground, replenishing our groundwater and stream water resources.

Although last winter was one of the least snowy on record for much of Pennsylvania, recent snowstorms in parts of the state have brightened the mood of snow enthusiasts who enjoy skiing, snowmobiling, snowshoeing, hunting, and ice fishing.

But forests blanketed in snow should also be appreciated by those who enjoy streams in the summer and rely on groundwater wells and springs for drinking water supplies. 

That’s because forests and snowpacks together allow for recharge of underground aquifers that consist of 80 trillion gallons of freshwater stored in the pore spaces and cracks in rock beneath the surface. 

These aquifers serve to maintain the flow of streams throughout the year and provide water that supports industries, businesses, agriculture, and drinking water for millions of Pennsylvania residents. 

In an average year, 10 percent to 25 percent of the water that flows in streams and enters groundwater wells originates from melting snow.

The forest creates a perfect environment to capture and slowly melt snow into the ground. The soil under forest canopies acts like a sponge to soak up and pass water from the surface into groundwater aquifers. 

Where forests are removed, the soil may become compacted or even paved, reducing the amount of water that can infiltrate into the ground to support aquifers. 

Infiltration of water into the ground occurs most efficiently during times when the forest is dormant. That’s where a thick snowpack becomes beneficial.

The snowpack that accumulates during the winter insulates the soil underneath it, keeping the soil largely unfrozen and able to absorb water from melting snow. 

Since trees and other plants are dormant during early spring, most of the snowmelt water entering the soil can infiltrate and recharge groundwater aquifers. 

The snowpack also represents a large volume of stored water that can be released slowly during the spring melt. 

A ten-inch snowpack covering just one acre may hold 30,000 gallons of water or more. 

Once the snow is gone and trees leaf-out in late spring, most infiltrating water from summer rain storms is taken up by the roots of the growing trees. 

This cycle results in high groundwater levels during March and April that typically fall throughout the summer and early fall.

Groundwater aquifers that are recharged in the spring by melting snow provide water supply wells and streams with a steady source of cool ground water during the long, hot summer. 

Fish and other stream life have adapted to the increased stream flows in spring and the relatively cool groundwater that is supplied to the stream throughout the summer. 

Without this spring recharge, stream levels may drop, and stream temperatures may increase to dangerous levels during the summer. 

So the next time you cast a fly over a rising trout or take a drink of water from your well or spring, remember that the combination of undisturbed forests and winter snowpacks provides much of the groundwater that we rely on every day.

(Reprinted from Penn State Extension Watershed Winds newsletter.  Click Here to sign up for your own copy.)

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[Posted: December 16, 2020]  PA Environment Digest