Explain How Rivers Adjust to a Change in Base Level, with Reference to Example(S) That You Have Studied

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Explain how rivers adjust to a change in base level, with reference to example(s) that you have studied. (30 marks) The base level of a river is the lowest level at which river erosion can take place, which is sea level. Changes in sea level over time can be a result of climate or tectonic activity. If the land level rises or the sea level falls, there is a drop in the base level. This will result in the land rising when compared to the sea level. The new river profile will now flow faster to the sea as vertical erosion cuts into the river bed. This process is called rejuvenation. New landforms such as knickpoints and paired terraces are formed as a result. Waterfalls are usually only found in the youthful stage of a river as the river runs down a steep slope, vertically eroding. Knickpoints are small waterfalls found in the lower course of a river. They occur at the point where the river once entered the sea. Due to isostatic uplift the sea level was lowered and the river had to now travel a longer distance to reach the sea. The river was “rejuvenated” as it was given renewed ability to vertically. The rejuvenated river cuts a new profile for itself and the place where the new profile meets the old profile is known as the knickpoint. An example of a knickpoint in Ireland can be seen on the River Erne in Co. Donegal at Kathleen’s Falls. When a former flood plain of the old age stage is uplifted, river rejuvenation affects this region to form the second feature I will discuss which are paired terraces. A new narrow flood plain is cut into the older, wider flood plain as hydraulic action, abrasion and most importantly vertical erosion is renewed. The river erodes the clay, silt and bedrock in its floodplain. The original valley floor is left high above the new floodplain and is seen as steps in the land on either side of the river. These steps are called paired terraces. Sometimes a river can be rejuvenated more than once and so another set of terraces are formed resulting in a river valley with stepped sides. Examples of paired terraces can be seen on the River Barrow in Co. Kilkenny. .

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Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour Thanos Papanicolaou University of Iowa, [email protected]
University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Final Reports & Technical Briefs from Mid-America Mid-America Transportation Center Transportation Center 2012 Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour Thanos Papanicolaou University of Iowa, [email protected] David M. Admiraal University of Nebraska-Lincoln, [email protected] Christopher Wilson University of Nebraska-Lincoln Clark W. Kephart University of Nebraska-Lincoln, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/matcreports Part of the Civil Engineering Commons Papanicolaou, Thanos; Admiraal, David M.; Wilson, Christopher; and Kephart, Clark W., "Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour" (2012). Final Reports & Technical Briefs from Mid-America Transportation Center. 3. http://digitalcommons.unl.edu/matcreports/3 This Article is brought to you for free and open access by the Mid-America Transportation Center at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Final Reports & Technical Briefs from Mid-America Transportation Center by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Report # MATC-UI-UNL: 471/424 Final Report 25-1121-0001-471, 25-1121-0001-424 Monitoring the Effects of Knickpoint Erosion ® on Bridge Pier and Abutment Structural Damage Due to Scour A.N. Thanos Papanicolaou, Ph.D. Professor Department of Civil and Environmental Engineering IIHR—Hydroscience & Engineering University of Iowa David M. Admiraal, Ph.D. Associate Professor Christopher Wilson, Ph.D. Assistant Research Scientist Clark Kephart Graduate Research Assistant 2012 A Cooperative Research Project sponsored by the U.S.
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