How do processes
involving water change
What is the MAJOR agent
of erosion that has shaped
Earth’s land surface?
Water moving over land’s
surface is called runoff.
This may cause sheet
The amount of
water runoff in an area
5 main factors:
1. The amount of rain an area receives.
2. Vegetation - grasses, shrubs & trees
3. Type of soil - some absorb more water
4. Shape of the land – steep slopes have
more run-off, which causes more erosion
5. How people use the land – parking lots &
crop removal increase run-off
How does runoff over
time affect the land
Rills & Gullies
Rills are tiny grooves in the soil
that grow larger forming gullies.
A gully is a large groove or channel
in the soil that carries runoff after
a storm. It moves soil & rocks.
Gullies only contain water after it
Streams & Rivers
Gullies join together to form a larger
channel called a stream.
Water continuously flows here and
rarely dries up.
Small streams may be called creeks or
Small streams flow together to form a
large stream called a river.
Rill erosion at a
Image by M. Mamo, Labels
added by UNL
Gully erosion in a pasture.
Image by NRCS
Streams grow together by getting
water from tributaries.
A tributary is a stream or river that
flows into a larger river.
An example: The Missouri & Ohio rivers
are tributaries of the Mississippi river.
Tributaries collect their water from the
drainage basin or watershed.
Features of rivers:
What features are
formed by erosion along
Where a river meets an area of hard &
slowly eroding rock
Then flows over softer rock downstream.
How does softer rock erode? What
results from this erosion? The softer
rock erodes away faster & a waterfall
Waterfalls at the
Plitvicka Jezera National Park in Croatia
What is a flood plain?
A wide valley in which a river flows
What happens to the land during a
The water in the river over flows its
banks into this wide river valley area.