Wednesday, June 8, 2011

Creek Reshaped

Small Streams change constantly. Sometimes the change is slow and gradual. At other times, a single storm can restructure an entire stream segment. Last year I showed a spot in the creek that was filling with gravel because of being partially blocked by a fallen tree. Early spring storms transformed this into an entirely different type of stream.

The gravel is gone. The sand and gravel I was working in as I fixed my bridge most likely originated from this spot.

The flood exposed older silt and sand deposits that existed beneath the loose gravel. Masses of roots helped slow the erosion caused by the rushing flood water. Roots were left strung out into the downstream pool. Fortunately there were enough roots left for the healthy regrowth of many plants.

Most of the tree is still intact, but it is no longer blocking the stream. The downward pointing branches that captured stream debris and formed the dam have been snapped off. With the branches gone, the debris moved on downstream and a clear passage remained. The errant section of bridge deck followed this route and probably played a part in moving things out of the way.

The stream channel ended up being much deeper than it was prior to the gravel deposition. As a result, there is no material left to hold the toe of the creek bank. This section of bank has already begun to slide into the creek, a portent of more changes to come.

Quite a few changes have occurred to this section in the last few years. The tree fell on a pebble bottomed creek that was wide and flat. The fallen tree caused gravel to fill the channel and made the creek even wider, but with a defined small channel on one side. Now the channel has narrowed and deepened and has a bed filled with large stones. Each condition provides habitat for a specific group of aquatic organisms. These are some very resilient animals to be able to shift from place to place as their preferred habitat moves about the creek.

The changes will continue. The stream as a whole seems to maintain a kind of balance with a certain number of blockages, pools, riffles and bottom conditions. Their positions may change, but all of the parts remain. Every time a major change occurs, my mind screams disaster, even though I know that this is just a natural condition for a headwater stream. Months later, when I see the abundance of life taking advantage of the new arrangement, I begin to feel comfortable with what’s happened. Usually, this is just in time for the next major event to start the whole process over.


  1. I enjoyed reading that.I was wondering if you happened to notice thru these changes if any species of your plants which prefer this habitat have expanded or declined or if perhaps you've gotton any new arrivals.

  2. Hi, Michael. If you were to take an annual inventory of plants growing within the creek channel, you would probably find the species and numbers to remain fairly constant. They all seem to colonize new locations about as rapidly as colonies are destroyed.

    Losses sometimes occur when a section of bank is lost or when the creek cuts a new channel. There have been occasions when I've rescued a plant on an eroding bank and moved it to a safer location. Most of the plants in the flood plain are abundant enough that the loss of one or two makes little difference.