Otter Creek in all of it's beauty is still subject to the natural process of erosion, largely but not exclusively in part that it is a tributary of the Ohio River. Excessive rainfall and the fact that there are numerous underground springs and waterways also contribute to it's erosion. Otter Creek meanders and bends along it's entire length, this is due to the fast flow of water along numerous banks over many years, as shown in the example below:
Stream banks erode for many reasons. Stream bank erosion is a natural process that over time has resulted in the formation of the productive floodplains and alluvial terraces common to the middle and lower reaches of Otter Creek.
Paradoxically, even stable river systems have some eroding banks. However, the rate at which erosion is occurring in stable systems is generally much slower and of a smaller scale than that which occurs in unstable systems.
Events like flooding can trigger dramatic and sudden changes in rivers and streams. However, land use and stream management can also trigger erosion responses. The responses can be complex, often resulting in accelerated rates of erosion and sometimes affecting stability for decades. Over-clearing of catchment and stream bank vegetation, poorly managed sand and gravel extraction, and stream straightening works are examples of management practices which result in accelerated rates of bank erosion. Erosion can also be accelerated by factors such as: • stream bed lowering or infill • inundation of bank soils followed by rapid drops in flow after flooding • saturation of banks from off-stream sources • redirection and acceleration of flow around infrastructure, obstructions, debris or vegetation within the stream channel • removal or disturbance of protective vegetation from stream banks as a result of trees falling from banks or through poorly managed stock grazing, clearing or fire • bank soil characteristics such as poor drainage or seams of readily erodible material within the bank profile • wave action generated by wind or boat wash; • excessive or inappropriate sand and gravel extraction • intense rainfall events (e.g. cyclones). 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. 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. By looking carefully at the processes operating at a site it may be possible to narrow down the probable causes of instability.
Bank scour Bank scour is the direct removal of bank materials by the physical action of flowing water and the sediment that it carries.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 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. The causes of these types of failures are often difficult to determine but can include natural and/or human factors. slumping as a result of saturation after flooding are common examples of mass failure.
In order to log this Earth Cache, please answer the questions below and send me an email with the answers. You may also post a picture of yourself if you like, but it is not required.
1. When I took the two photos above, I was standing on "something" at the GZ, do you believe that erosion had any effect on it's current condition?
2. Does this area suffer from Bank Scour?
3. Do you see evidence of any Mass Failure here?
Please be extremely careful while visiting this Earth Cache, the banks can give way if you are not careful.