Rivers

1. Rivers Mrs. Overton January 2013

9. Youthful River • Youth • a river that is full of splash and vigor • Has a lot of erosive energy • Forms V-Shaped Valley • Rapids • Waterfalls • No Flood Plain • Drainage Divides Broad and Flat, Undissected by Erosion • Valley Being Deepened • It can carry large sediment • No meanders • Steep gradient

10. Mature River • Maturity (Late) • It is slower • It cuts back the sides of the valley depositing materials, forming flood plains • Valley has flat bottom • River begins to meander • Sediment builds up • Divides begin to round off • Wider instead of deeper • Large watershed • Less steep gradient • Some tributaries

11. Old River • Old Age • Broad flood plains • Extremely wide meanders • Oxbow lakes • Resistant rocks • Low gradient • Little erosive energy • Few tributaries • Flood plains are flat • Good place for farming • Lots of sediment • Meander scars

12. Rejuvenated River • Rejuvenation • Uplift of land raised by tectonic activity • Because of land rising, the gradient becomes steeper and the river flows more quickly. • Uplift of Land causes stream to speed up and cut deeper. • Stream valley takes on youthful characteristics but retains features of older stages as well. • Terraces are formed on both sides of the valley • Can happen at any point in the cycle • Example: Grand Canyon

13. Waterfall • A waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff. • form where the channel slope becomes steeper or is composed of varying bands of soft and hard rock. erosion (occur when the volume or speed of the flow of water increased), hydraulic action and abrasion will cause the water to fall from a higher level to a lower level.

14. Meander • A meander is formed when the moving water in a river erodes the outer banks and widens its valley. • Erosion and deposition occurs at the bend of the river. the speed is greater on the outside of the bend therefore erosion occurs on the outside while deposition on the inside.

15. Ox Bow Lake • An oxbow lake is a U-shaped body of water formed when a wide meander from the main stem of a river is cut off to create a lake • As the opposite bends erode towards echother, the neck of a meander will get progressively narrower until, during a period ofhigh discharge, the river will cut through to form an oxbow lake. • at the upper course, the landforms present are Floodplains and levees.

16. An overview

17. When they are young, rivers ideally start out relatively straight in map view, entrenched in V-shaped valleys. You’ll also find plenty of waterfalls and rapids at this “Youth” stage. As time goes by, the river erodes downward to base level, and loses the gravitational impetus to incise any deeper. The river now begins to meander side to side, and as it does so, enlarges the size of its valley by lateral erosion at cut banks. It is “Mature.” As time goes by, the valley walls get further and further apart. …Then what?

18. If enough time goes by, the river can enlarge the size of its valley so much that you can’t really tell it’s a valley any more. At this stage, meandering can get pronounced enough to fold back on itself and create oxbow lakes (visible in the map view of the “Old Age” stage). The story could conceivably end here. However, if base level were to drop anew, the river will begin to incise again, producing a valley profile (cross-section) that looks pretty much identical to the “Youth” stage. It has been made young again, or “Rejuvenated.” In map view, however, you can see from the meandering shape of the re-incised valley that the river must once have been at the “Old Age” stage. There are no more oxbow lakes in the “Rejuvenated” stage, as the river’s energy is going into downcutting rather than lateral meandering.