Moose Jaw Meandering River EarthCache

Moose Jaw Meandering River

A Meander, in general, is a bend in a watercourse or river. A meander forms when moving water in a stream erodes the outer banks and widens its valley, and the inner part of the river has less energy and deposits silt. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the inside. The result is a snaking pattern as the stream meanders back and forth across its down-valley axis. When a meander gets cut off from the main stream, an oxbow lake forms. Over time meanders migrate downstream, sometimes in such a short time as to create civil engineering problems for local municipalities attempting to maintain stable roads and bridges.

There is not yet full consistency or standardization of scientific terminology used to describe watercourses. A variety of symbols and schemes exist. Parameters based on mathematical formulae or numerical data vary as well, depending on the database used by the theorist. Unless otherwise defined in a specific scheme "meandering" and "sinuosity" here are synonymous and mean any repetitious pattern of bends, or waveforms. In some schemes, "meandering" applies only to rivers with exaggerated circular loops or secondary meanders; that is, meanders on meanders.

Sinuosity is one of the channel types that a stream may assume over all or part of its course. All streams are sinuous at some time in their geologic history over some part of their length.

The above picture demonstrates the nature of a meander. A meander consists of three parts: the outward side of the river bend, which is called the concave portion, the inner side of the river bend or convex portion and the straight area between successive bends, which is called the point of inflection because it marks the point at which the curvature changes or inflects from one direction to the other. A river section has a length which is considered to be the distance the river travels over the ground and not the crow-fly distance between two points. It also has a width and a depth. Because a meandering river has alternating bends, it is like a wave and therefore has an amplitude, a wavelength, and a radius of curvature. The amplitude is the distance along the ground that the river bend extends away from the overall downward path of the river. The wavelength is the distance along the ground between successive bends that are in the same direction. The radius of curvature is like the radius of a circle; for a bend in a river, it is the radius of the arc that the bend makes.

A wide variety of river and stream channel types exist in limnology, the study of inland waters. All these can be divided into two groups by using the water-flow gradient as either low gradient channels for streams or rivers with less than two percent (2%) flow gradient, or high gradient channels for those with greater than a 2% gradient.

Low gradient channels Low gradient channels of rivers and streams can be divided into braided rivers, wandering rivers, single thread sinuous rivers (meandering), and anastomosing rivers. The channel type developed depends on stream gradient, riparian vegetation and sediment supply. Braided rivers tend to occur on steeper gradients where there is a large supply of sediment for braid bars, while single thread sinous channels occur where there is a lower sediment supply for point bars. Anastomosing channels are multithreaded, but are much more stable than braided channels and commonly have thick clay and silt banks and occur at lower gradients of stream bed. Wandering rivers fall between sinuous single thread and braided streams and are relatively stable multi-channel gravel bed rivers.

High gradient channels High gradient channels of rivers and streams have been divided into riffle-pool (which can cover all of the low gradient channel morphologies discussed above), rapid/plane bed, step-pool and cascade unit morphologies.

Riffle-pool sequence channels are composed of migrating pools and transverse bars called riffles and occur on gradients less than 1-2 percent. Rapids (also called plane bed, but not to be confused with the plane beds described in sand bed rivers) lack distinct pools and bars but commonly have stone cells or clusters and occur on gradients in the range of 1-5 percent, and have "whitewater". Step-pools are composed of channel-spanning pools and boulder/cobble steps that cause subcritical flow in the pool and supercritical flow over the steps. They occur in gradients in the range of 5 and 20%. Cascade units exist at steeper gradients (approx > 10–15 percent) where the channel is dominated by boulders and cobbles and channel spanning pools do not exist. Pocket pools are common. In all four channel types large woody debris may strongly influence the channel type.

To claim this earth cache, provide answers to the following questions...

1. At the starting point you are standing near the banks of two parts of the Moose Jaw River Meander. These two banks would be called One Concave bank and one Convex bank , Two Concave banks, Two Convex banks, or Neither?? What is the distance from the west edge of the fence to the east edge of the fence. This is basically the top edge of the Meander and what remains of the original bank.
2. At Meander3 looking across to the opposite shore to the South calculate the height of this bank?? Basically, the bank to the south is the same altitude difference of Meander3 and the starting point?? There are two stream channel types by using the water-flow gradient, which would this stream be considered a low gradient channel or a high gradient channel??
3. At either of the Meander points which way is the river flowing. Then consider when at the starting point which way the river might be travelling on either side of the banks??
4. Measure the distances from Meander2 and Meander4?? At this time these are the narrowest points between the both sides of the Meander. Depending how the Moose Jaw River erosion continues, this could start shifting towards the west further inwards. Causing the meander to change shape even further.
5. Eventually, if events continue, what in your estimation will happen with the Meander?? Give an explanation as to your reasoning...
6. Optional: As always pictures are welcome of yourself at either of the four Meander points.


Thanks and Enjoy...

LaDeBA...