Erosion is the process by which soil and rock are removed from the Earth's surface by natural processes such as wind or water flow, and then transported and deposited in other locations.
The four main types of erosion are Water, Wind, Gravitational and Exfoliation.
For this lesson, we will be dealing with Water erosion of which there are six different types, however we will be learning about River erosion and more specifically Bank erosion.
Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from changes on the bed of the watercourse, which is referred to as scour. One way of measuring erosion and changes in the form of river banks may be done by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times, however you will not need to do this in this case.
Processes of Stream Bank Erosion
The various mechanisms of stream bank erosion generally fall into two main groups, bank scour and mass failure. In many cases of bank instability both will be evident, often with either scour or mass failure being dominant. Bank scour is the direct removal of bank materials by the physical action of flowing water and is often dominant in smaller streams and the upper reaches of larger streams and rivers. Mass failure, which includes bank collapse and slumping, is where large chunks of bank material become unstable and topple into the stream or river in single events. Mass failure is often dominant in the lower reaches of large streams and often occurs in association with scouring of the lower banks.
Bank scour is the direct removal of bank materials by the physical action of flowing water and the sediment that it carries. As flow speed increases, the erosive power of flowing water also increases and scour may occur. Increases in flow speed can be the result of natural and/or human induced processes. Undercutting of the bank toe is an obvious sign of scour processes. Effective strategies for combating scour are generally aimed at reducing flow speed through revegetation and in some cases through strategic bank or channel works.
Mass failure describes the various mechanisms of bank erosion that result in sections of the bank sliding or toppling into the stream. Mass failure is sometimes described as collapse or slumping. Bare and near-vertical banks or areas of slumped bank materials are obvious signs of these processes. Th causes of these types of failures are often difficult to determine but can include natural and/or human factors. Collapse following undermining of the bank toe and slumping as a result of saturation after flooding are common examples of mass failure. Effective strategies for combating slumping or bank collapse are generally aimed at stabilizing the bank toe and restoring bank vegetation.
By looking carefully at the processes operating at a site it may be possible to narrow down the probable causes of instability.
The posted coordinates will bring you alongside Sixteen Mile Creek, which runs from the Niagara Escarpment through Milton and Oakville and flows into Lake Ontario. Here you can observe how erosion has taken its toll on the banks of Sixteen Mile Creek, both affecting the natural bank and also how it has affected man's attempt to prevent erosion of the bank.
In order to log this Earthcache, you will need to visit the posted coordinates where you will be able to get an excellent perspective of the bank on the opposite side of the river and be able to make your observations on the erosion process and then email me the following information from your findings:
1) What type of bank erosion (bank scour or mass failure) is taking place on the opposite side of the river here and what evidence do you see to back up your observations?
2) What has man done to try and prevent the bank from eroding and has it been successful, why or why not?
3) Using your gps, walk along parallel to the river and calculate the distance that the erosion is prominent and evident on the opposite bank.
4) What would eventually happen here to Sixteen Mile Creek if man did not intervene to try and curtail the erosion process?