April 16, 2005

Between April 10 and April 13 a tall Maple tree toppled into the stream. This tree was situated only about 20-30 feet upstream from the Tulip tree that fell into the stream in August 2004. Prior to its fall it showed no real sign that anything imminent was about to occur. It remained straight, without any hint that it was leaning over towards the stream. During the period that it fell, the exact day is unknown, there were not major rain storms and there were no significant winds that would have prompted it to fall. It appears that the soil along the bank had been sufficiently washed away in large storms over the preceding few weeks and the very wet soil at the time were sufficient to weakening the hold that the trees roots had in the ground. The tree itself was about 100 feet tall and had a girth of about 42 inches. That made it just over a foot in diameter. When it fell it landed alongside of the large Tulip tree. So now the two are laying side by side in the stream.

On the map the tree had been located at the coordinates of about (85,5). For the non math inclined that puts it in lower right hand corner of the map. That is exactly where the stream takes a sudden right turn. The red line marks one side of the steam at the approximate location of the stream bank. The water flows down stream from the upper right. So the most significant erosion happens at and just past the bend in the stream.

The next two trees that should fall are to the left of where the Tulip tree was situated. On the map that is about at the bottom center. For now those two trees are at least partially being protected by the large root balls of the two trees that have fallen.

The map has also been updated for some additional erosion that has occurred along the stream bank. Most of those changes were very minor, involving a loss of a foot or two of soil from the bank. So they are not readily apparent on the map.

August 7, 2004

On August 4, 2004 in the middle of a major rain event the big Tulip tree that was the original focus of Tree and Stream toppled into the stream. With it went a piece of the stream bank about 15 by 20 feet. We had lost six inches of rain in six day and 3.5 inches in about 26 hours. The steam filled past bank full, and in places flowed into the food plain. The rush of water was just too much for an already leaning tree. Half the roots were gone by then and the soil under the tree itself as seriously eroded. The fall was inevitable. The tree itself was likely close to a hundred years old and stood about 120 feet tall. So it was no small tree.

I updated the map of the stream bank a few days after the storm. The first thing to note is that the scale on the left has changed. It now goes down to -10 instead of zero.

The changes from the previous revision two months earlier are readily apparent. The tree stood on a major bend in the stream so that is the area where most of the erosion is taking place. The bend is still there so more erosion will continue. There are two large Tulip trees standing on the new bank of the stream. One is seriously ill. A couple of years ago a beaver stripped all of the bark around the base of that tree. It has been slowly dying ever since. The second tree is still very healthy. But it will be the next to go.

The immediate future changes along the stream bank will largely depend on how the tree interacts with the stream. Currently there is a rather large root ball laying in the middle of the steam. There is no water getting by between the root ball and the stream bank. As a result all of the water is forced to flow under the tree itself. Wiht time the root wall will wash away and things will change once again.

June 24, 2004

After a couple of big storms in June of 2004 enough of the stream bank had eroded along one stretch that I though it was time to update the map of the stream bank. The first storm dropped over 3.5 inches of rain. My estimate for the second storm was 3 inches. The changes were not major, however since is had been nine months since I posted the organal map I did want to reflect the fact that the page was up to date.

While I had not been monitoring the stream bank along that stretch closely I belive most of the erosion occurred due to the two storms. The erosion occurred on either side of "the Tree." I had expected some erosion upstream from "the Tree." But the down stream erosion was a surprise. It was not an area where I did not expected much erosion to take place. My expectation was that it would occur in the stream just prior to "the tree" rather than just past "the tree." I suspect that when the steam reached close to bank full in a storm in early June the water flowed across point bar 2 and this directed the flow to the area the eroded. A small island had begun to form in that area in the previous month. Originally I thought that the clearing of some of the debris in the center of the stream had allowed this to occur. But perhaps more importantly it happened because of the greater width of the stream. In fact the bank only lost about a foot in each place. So the change was not that great.

A close comparison of the two maps is necessary to even notice the changes. It also seems that the land just prior to the tree is "sinking a bit. It is a bit lower now than most of the neighboring steam bank.

September 15, 2003

In September 2003 I laid out a grid along the stream bank so I could measure the movement of the stream bed over time. This was intended to provide a more accurate measurement of a small section of the stream bank than could be obtained with my GPS. The work was completed just before Hurricane Isabel came through the area. In the end the rush was not necessary as the hurricane did nothing to move the stream bank.

I first set up a line of poles at 20 foot intervals along the bank behind the tree. Then I attempted to set up a second line of poles upstream and around the bend in the stream. This line is almost laid out at right angles to the first line. I then measured the distance from the lime made by the poles to the top of the stream bank on the same side of the stream as the tree sits.

With a bit of trigonometry I adjusted the measurements for the fact that the two lines were not laid out a precise right angle. The chart on the right is the result of these measurements. In this chart the stream flows down from the top right around the bend and past the tree ending up in the lower left hand corner. I have not shown the sharp left turn the stream takes after that point. The measurements in this chart are in feet.

At one time the major erosion was taking place to the left of the tree. However over time the very sharp bend in the lower right was created. Currently that is where most of the erosion occurs at this time (September 2003). As the water rounds the curve and passes the tree it is currently being forced to the other side of the stream bed. So there does not seem to be as much erosion to the left of the tree. I expect this situation to continue until after the tree falls into the stream.