Life Cycle of a Stream Aim: How does a river shape the land over time?

In the beginning…. A single heavy rain may form a small valley in loose soil along a hill slope When the rain ends, the small valley remains (this is called a gully) These will grow in length, and depth and may cut down far enough to become permanent. (Downcutting)

Youthful Stage During this stage a river may capture the headwaters of another river through the process of headward erosion. This is called stream piracy.

Youthful Rivers Youthful rivers have fairly straight channels and steep gradients

Youthful Stage V-shaped valley –Water erodes the sides of the valley walls and the river cuts down into its channel –The upper valley walls are widened into a v-shape

Youthful Stage Rapids Waterfalls

Maturity When sidecutting (lateral erosion) becomes greater than downcutting The topography becomes less steep with a smoother gradient Floodplains form The stream begins to meander Meandering River

Meander

Floodplains The land between the stream and the steep walls of the valley that is usually covered when the river overflows its banks during a flood Natural levees form along the banks of the river

Manmade levees are built to protect nearby areas when a river overflows its banks

Old Age Meanders become cut off from the river forming oxbow lakes A river officially enters old age when the flood plain becomes wide enough to accommodate all of the meanders

Oxbow Lakes

Summary of Stages