Rivers, Floods and Management: River Rejuvenation

Rivers, Floods and Management: River Rejuvenation

1. What is Rejuvenation?

   • Over a long period, a river assumes a generally smooth long profile. This is the most efficient profile for a river to have in order to transport water and sediment.
   • The river reaches a state of equilibrium, however occasionally an event occurs that de-stabilises the situation, and causes the river to actively erode its channel in order to re-establish its smooth long profile.
   • Rejuvenation is the restoring period of river erosion resulting from a fall in base level.

2. How Does a River Become Rejuvenated?

   • The sudden and rapid increase in erosion is due to a fall in base level.
   • If base level falls, a 'kink' or step called a knick point is formed in the river's long profile.
   • The increase in gradient caused by the fall in base level means that now the river has more energy available. This energy is used to actively erode the irregularity, so that the river once again achieves a state of equilibrium by creating a smooth long profile
   • One of the causes of rejuvenation is sea-level change. If sea-levels fall faster than the rate of vertical erosion, a knick point will form close to the coast
   • Another cause of rejuvenation is river capture. Over hundreds of years, rivers gradually cut backwards at their source. this is called headward erosion. Occasionally, as a river cuts back, it can break into an adjacent valley and 'capture' the tributaries of the nearby river. A waterfall is often formed as result in difference in height. this is a knick point, and as the river cuts into its former valley, features of rejuvenation will be formed.

3. The Different Changes in Rejuvenation

   • Eustatic change-global- is the change in sea level caused by a change in the volume of water in the ocean store.
   • Isostatic change-local- is sea level change caused by a change in the level of the land relative to the level of the sea.