Outcomes:
Describe the three stages in the life cycle of a river.
State two ways in which water erosion occurs.
Examine evidence to determine the life cycle stage of a river.
River Life Cycle
Drainage Basin is the area of land drained by a river and its tributaries.
Rivers change over time and to go through three stages:
1. Youth
2. Maturity
3. Old Age
 Youth (figure 2.7 p.28)
o Are usually found in highland or mountain regions
o They tend to have a steep slope (high gradient)
o Usually have a small volume of water
o They have a rapid flow of water
o There is usually very rapid erosion especially vertically
o A narrow “V” shaped valley is characteristic
o Waterfalls and rapids are common

Maturity (figure 2.7 p.28)
o Most high relief is eroded
o Gentler slope
o Many well developed tributaries
o Broad flat river valley
o Well developed flood plain
o More lateral erosion than vertical
o Meandering results
 Late Maturity (figure 2.7 p.28)
o Remember the stages are not distinct.
o These changes occur over long periods of time
 Old Age (figure 2.7 p.28)
o Almost no slope
o Very little relief
o Elaborate meandering
o Oxbow lakes develop
o Often swampy areas around river
o Very muddy due to slow speed
o Most susceptible to flooding because of large flood plain.
Evaluating Evidence to Determine the Age of Rivers
There are six common pieces of evidence you can look for to determine the stage of a river.
1. Slope of the river (steeper = younger)
2. Relief of the banks (steeper = younger)
3. Width of the valley (wider = older)
4. Meandering (more = older)
5. Size of flood plain (wider = older)
6. Rapids or water falls (more = younger)
Two Directions of River Erosion
1. Vertical erosion makes rivers deeper as is the case in young rivers
2. Lateral erosion makes rivers wider leading to the meandering of mature rivers.