A Tiny Dam

by Carl Strang

Back in April, a series of heavy rains resulted in some unusual flooding in DuPage County.

Water poured across the trail at Mayslake Forest Preserve.

Water poured across the trail at Mayslake Forest Preserve.

The swift waters had a scouring effect, and small streams county wide that previously had silt bottoms now were gravel bedded.

The stream at Mayslake was one example.

The stream at Mayslake was one example.

Now, more than 7 months later, the gravel continues to dominate wherever the water has continued to flow with any strength. It doesn’t take much to alter this, however. On a recent exploration of the lower part of Mayslake’s stream I found an elongate pool backed by a tiny dam.

The dam was formed by tree roots which captured a few sticks, with gaps filled by drifting leaves and other debris.

The dam was formed by tree roots which captured a few sticks, with gaps filled by drifting leaves and other debris.

Immediately below the dam, and above the pool, the stream remains gravel floored. In the pool, however, the gravel has become obscured by silt and organic detritus. This diversifies the ecology of the stream, as different invertebrates favor different substrates.

The pool above the dam

The pool above the dam

Little lessons in ecology, geology and change are always out there for us to discover and appreciate.

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