Naturalist's Notes

Linking our Forests and Water Together...

By Paul Lumia • November 15 2011

Linking our Forests and Water Together: Permeability – Why We Need to Preserve Our Forests.

“Permeability: A measure of the relative ease with which water will move through soil or rock.” (Ohio State University Extension Fact Sheet: Food, Agricultural and Biological Engineering)

Waters’ ability to pass through, or infiltrate, something is based on that object’s permeability. The more compact and less porous a surface, the less permeable it typically is; take for instance concrete versus a forest floor. On a concrete surface such as a depression on a sidewalk a puddle of water remains until it has evaporated or been swept away. On the other hand, take that same amount of water from that puddle on the concrete and place it on the forest floor. It would be absorbed, infiltrated, translocated, and rarely pool except in times of saturation.

A picture from my childhood memories comes to mind when I think of this subject. Having grown up in suburbia, whenever it rained excessively the gutters on the street where I lived would often overflow as the water gathered and headed to the storm drain. In the hot summers when this happened my neighbor’s children (friends at the time) from across the street could be found tubing! All the runoff from the roofs, and roads, side walks and driveways was on its way down the gutter, all of that water running off impervious surfaces making a suburban river.

When the clouds gather and the rain comes down, the water has to go somewhere, something with which all of us here in the Susquehanna River Basin are all too familiar! Whether by evaporation, surface run off, or infiltration, water is always on the move as part of the perpetual water cycle.

Our forest floors act as highly permeable sponges, allowing some of water to infiltrate and enter the ground water system. The typically loose surface of a forest floor with its leaf litter, woody debris, root systems and soils can absorb quite a bit of water before becoming saturated and the rain becomes runoff. Soil surfaces become less permeable from activities that cause compaction. As a surface becomes less permeable an increasing amount of water remains on the surface creating a greater potential for flooding.

With multiple studies on the books and by understanding the relationship of water movement and how our forests can help alleviate excess surface runoff, it becomes clear that preserving them is increasingly beneficial.

By seeking to preserve our precious lands forever, North Branch Land Trust works with land owners to preserve their forests and fields. Along with the memories tied to these lands, the natural habitats provided, and view sheds being preserved, another benefit of conservation is that our permeable surfaces are being retained! Flooding happens, but with less and less permeable surfaces, areas are at a greater risk due to increased runoff. We are helping to keep our forests intact and provide this function of infiltration.

by Rylan Coker
Land Protection Specialist

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