Xtra Bends in a Stream EarthCache

1. There are three locations for you to visit.
2. The first location has nearby parking. Be careful as you walk the short distance to the cache site. Traffic can be heavy at times.
3. The final two locations are about 150' apart and not far from the first location. You can drive or walk to them.
4. At each of the locations you will be on a bridge crossing the stream.
5. There is no reason to go down to the stream at any of the locations.
6. There are other caches in the area that you may want to visit while you are here. Be sure to take out any trash that you may create during your visit.
7. Have fun.

1. Briefly describe the geological processes that cause meandering.
2. Is the water in a stream moving faster on the inside bend of a meander or the outside bend of a meander?
3. Name one problem that could be caused by the development of a meander in a streambed.

1. If you observed the banks of the stream on each side of the bridge you should notice a distinct similarity which appears to have moved from one side of the stream to the other. You DO NOT have to send in any answers about this, but make note of it to compare it to the final location.
2. At the posted coordinates would you say the water is flowing very fast, moderately fast, slow or not moving? If it is not moving is it because it is moving so slow that you cannot detect any motion or because there is no water in the channel?
3. At the posted coordinates look upstream (south side of the bridge). As you look upstream does the stream bend to the east (left), west (right) or is it straight?
4. At the posted coordinates look downstream (north side of the bridge). As you look downstream does the stream bend to the east (right), west (left) or is it straight?
5. While you are still looking downstream are there any specific signs of erosion that you can notice along the streambed? (Hint: look to your right) If so, briefly describe what they are and which bank are they on (east or west)?

1. At location 2 you should be able to see 2 distinct bends in the stream. Would you say that the second one occurs immediately after the first, or is there a straight section between them?

1. At the posted coordinates would you say the water is flowing very fast, moderately fast, slow or not moving? If it is not moving is it because it is moving so slow that you cannot detect any motion or because there is no water in the channel?
2. At the posted coordinates directly below you. Which bank of the stream is on the outside of the curve at this location, furthest away or closest to the bridge?

1. This stream is only VERY slowly changing its' course due to erosion and deposition. Based on your observations at locations 1 and 3, why do you think that the meanders are not developing quicker?

1. Pictures are always nice, but do not include any spoilers.

MEANDERING STREAMS - INTRODUCTION

Have you ever noticed that a lot of streams and rivers follow a very curvy path as they flow downstream? This is referred to as meandering. However, if you look at the surrounding landscape you might notice that it does not have natural features that would cause the stream to take that kind of path. It is interesting to notice that the banks on the opposite sides of the stream may look very different from each other. On one side of the stream it might be fairly level, and not very far above the surface of the stream itself. It might be somewhat sandy or have smaller pebbles on the surface. The other side might have a steep slope with areas that are undercut with exposed roots and rocks. All of this is caused by the dynamics of the water flow, and two very natural processes - erosion and deposition.

MEANDER - A winding curve or bend in the stream.

EROSION - A process that wears away the surface of the earth. This can be caused by the action of water, glaciers, winds, etc. Erosion along a stream bed is at least partially, if not entirely caused by the action of water.

DEPOSTION - A geological process in which sediments are added to the landform. In the case of a meandering stream the deposition process is a result of the slowing of the stream, and suspended solids falling out of the water.

FORMATION OF MEANDERING STREAMS

Often streams are formed by water draining from a higher elevation to a lower elevation, often with a fairly steep slope. As the water runs down the steep slope it tends to follow the natural contour of the area and eventually erodes away a well defined path for the drainage. These paths tend to be straight unless they have to change directions to go around obstacles on the way down. Eventually the water reaches a more gentle slope along wider valley floors on their way to larger streams, rivers, lakes, etc. It is in these middle reaches of the drainage that menaders tend to form.

The picture below shows a small stream in the upper portion of its' drainage. Notice that there are no significant bends in the stream - the only bends are at obstructions it encounters as it flows down the hill. Note, the slope of this hill is steeper than it appears in the picture.

The next picture shows a stream along the middle reaches of its' drainage. Notice that the land is quite flat surrounding this stream. It is cutting through an agricultural field, and it appears as though the farmer has built up the height of the banks some to keep it from washing into the fields. It is in the beginning stages of forming meanders. Unfortunately for the farmer it is a natural process to form the bends, and to continue shaping them. Unless this farmer continues to work to keep the stream in the existing streambed it will over time continue to widen the meanders and break into the the fields.

Next is a picture which was taken from Google Earth and modified to highlight the creek in this area. This shows a view of French Creek near Cambridge Springs, PA. It clearly shows a very well developed meandering stream. Again, if natural process are allowed to continue here you can see where it could cause severe damage to a road (bottom right) and several agricultural areas. It is likely that steps have been taken to keep the creek within its' existing bed.

The final picture which was taken from Google Earth and modified to highlight an oxbow lake in this area. This shows a view of French Creek near Cambridge Springs, PA. It clearly shows an oxbow lake with a classic shape. The oxbow lake shows where the creekbed used to be. But at some time in the past it was choked off by deposition and straightened out the course of the creek in this section. If you view this area on Google Earth and pan along the creek you will see many of these oxbow lakes along the way.

PROBLEMS CAUSED BY MEANDERS

Meanders are formed as part of the natural life cycle of a stream. If the stream is in a remote area this does not usually create any problems, but for streams in populated or agricultural areas this can be a problem. Meanders can eventually take over fields in agricultural areas. In urban areas any uncontrolled erosion can eventually result in loss of land and possible destruction of buildings, roads and other structures in the area. Most meanders are formed over a fairly long period of time, and their effects can be monitored in critical areas, but sudden storm events can cause severe erosion and catastrophic damage. Steps need to be taken early to prevent serious damage later on.

There are many methods that can be used to mitigate bank erosion in agricultuaral and urban areas. Some examples are rock riprap, concrete lined channels and gabions. Sometimes just the planting of vegetation or modifications to the landscaping can be effective. A discussion of these methods is beyond the scope of this earthcache.