Tree in Creek

The only way to keep a stream from changing is to keep it in a picture. A stream is a dynamic entity that constantly changes its appearance. Ten years ago, this section of creek flowed over an 18 inch layer of gravel and mud before falling into the pool shown at the bottom of the photo. A tree falling across the channel began a series of events that are still changing the way this creek behaves.

The tree was dead when it fell and the trunk was straight. Initially, it rested about eight inches above the stream bed. Normal water flow was able to pass beneath this log bridge, but rain runoff was blocked and forced to come over the top. The force of the water coming over the top of the log dislodged the mud and gravel, creating a large pool. As the gravel bounced along the stream bed, more mud and gravel were kicked up into the moving water and carried away. The process slowed when larger rock pieces were encountered. The result was a deeper stream channel and the creation of vertical banks.

The pool still exists below the log, but the water lacks the energy required to move the larger stones, so the pool remains shallow. The newly exposed banks are not stable and are allowing the water to come around one side of the log. Through the years, the water soaked log has bowed and followed the descent of the stream bed. This phenomenon greatly increased the log’s effectiveness as a stream changer. It won’t be long before the log decomposes enough to break apart and be carried downstream.

When the tree first fell, heavy water flows would accelerate the speed of the water moving beneath the log. The fast moving water created an upstream extension of the pool and created a slight drop resembling a mini waterfall. Water passing over this drop increased slightly in speed and carried away some of the mud and gravel. As this process continued, the elevation drop moved upstream. Eventually, the mud and gravel was completely removed from the stream.

A single fallen tree caused several hundred feet of stream in both directions to change from a mud gravel bottom to a clean rock bottom. The rock bottom is more typical of small streams in the upper portion of this watershed and there seems to be a greater abundance of organisms now living in this stretch of stream. There are more trees that look as if they might fall in the future. It’s possible that another tree could fall and start the process of reestablishing a mud and gravel bed.

Intermittent Stream

During the winter, little water courses that have remained dry through the summer and fall begin to flow. Areas that haven’t had open water for half a year now have an abundance of small pools.

The water has filtered down through the soil on the wooded hillsides and appears as a narrow stream. The water is clear and clean. Winter birds prefer this water source over all others.

Storm runoff carries away leaves that have fallen into the stream channel. The water will continue to flow until mid spring and then things will again be dry. This type of seasonal flow defines an intermittent stream.

The small intermittent streams at Blue Jay Barrens are very nutrient poor and generally don’t support any algae or other plant life. Rain runoff removes sediment from the narrow channel so the substrate is generally rock. Several types of aquatic insects will lay their eggs in these streams in early spring.

There are some animal species that live exclusively in these tiny watercourses. A common one here is the flatworm know as the planarian. Planarians lay two types of eggs; one thin shelled that hatches soon after being laid and a second that is hard shelled and able to survive through the summer dry period. The eggs are hatching now, but the worms won’t be noticeable until late winter. Until then, I’ll just enjoy the sight of super clear water that flows in these streams.