Explain the concept of river rejuvenation, its causes, and the resulting landforms, including a description of a cross-section.

Here are the solutions to the questions about river rejuvenation:

1.1.1

River rejuvenation is the process where a river gains renewed erosive power, often due to a fall in its base level or an uplift of the land. This leads to renewed downcutting into its own floodplain and the formation of new landforms.

1.1.2

Two possible causes of river rejuvenation are:

• A fall in sea level (eustatic change), which lowers the river's base level.
• An uplift of the land (isostatic change) due to tectonic activity, which increases the river's gradient.

1.1.3

A labelled free-hand cross-section from A to B would show:

• a) Shape of the rejuvenated valley: A narrower, deeper, often V-shaped valley incised into the older, wider valley.
• b) Indication of the new flood plain: A relatively narrow, flat area at the bottom of the incised valley, adjacent to the current river channel.
• c) Indication of terraces: Step-like, flat surfaces on either side of the new valley, representing the remnants of the former, higher floodplain.

The cross-section would look like this (description, as drawing is not possible):

       Terrace (old floodplain)
      /----------------------\
     /                        \
    /                          \
   |                            |
   |                            |
   |                            |
   |      New V-shaped valley   |
   |     /---------------\      |
   |    /                 \     |
   |   |  New Floodplain   |    |
   |   |  ---------------  |    |
   |   |   River Channel   |    |
   |   \___________________/    |
   \____________________________/

1.1.4

River terraces form when a river, after a period of rejuvenation, cuts down into its own previously formed floodplain.

1. Initially, the river flows across a wide floodplain, depositing sediment.
2. When rejuvenation occurs (e.g., due to land uplift or a fall in sea level), the river gains renewed energy and begins to vertically erode (downcut) into its existing floodplain.
3. The former floodplain is left standing at a higher elevation on either side of the newly incised channel, forming flat, step-like features known as river terraces.

1.1.5

The illustrated rejuvenated landscape will negatively impact infrastructure development in several ways:

• The steep-sided, incised valleys and narrow floodplains make it difficult and expensive to construct linear infrastructure like roads, railways, and pipelines, often requiring extensive cutting, filling, or the construction of bridges and tunnels.
• The terraced landscape creates multiple levels, which complicates urban planning and the layout of services, as development areas are fragmented and require more complex grading.
• The steep slopes created by rejuvenation are prone to landslides and soil erosion, posing significant risks to the stability and safety of buildings and infrastructure built on or near them.