Chapter 9, Section 1
SURFACE WATER
Runoff
 What
happens to
rainwater?
1. Soak into the ground
2. Evaporate
3. Runoff
Runoff
 Runoff
 Water that flows across the surface of
the Earth
 Occurs when no more water can soak
into the ground
Runoff
 Factors
 Amount of rain
Affecting  Length of time that rain falls
Runoff
 Slope
 More runoff occurs on steeper slopes
 Vegetation
 More runoff occurs in areas with little
vegetation
Runoff
 Effects of  As water runs down a slope it increases in
Gravity
speed.
 Increased speed gives the water more
energy, allowing it to carry more
sediments
Water Erosion
 Rill and
 A small stream forms during heavy rains
Gully
Erosion
 The stream continues to travel the same
path forming a small channel called a rill
 As the rill becomes broader and deeper it
forms a gully
Water Erosion
 Sheet
Erosion
 Erosion that is caused by water flowing
in a broad sheet across the land
Water Erosion
 Stream
Erosion
 Erosion that occurs along the bottom and
sides of a stream
 Stream erosion can also occur by abrasion
 Stream load
 The sediments that are carried by a stream
 3 types
 Suspended load
 Lightweight particles that are carried in the water
 Bed load
 Heavier particles that roll along the bottom
 Dissolved load
 Dissolved rocks that are carried in solution
River System Development
 River
Systems
 A river system is like a tree with water
flowing into rills and gullies, then into
small streams, then into larger stream,
then into rivers, etc.
River System Development
 Drainage
Basin
 Area of land from which a stream or river
collects runoff
 All water in a drainage basin flows
towards the trunk, or main river
Stages of Stream Development
 Stages of
Stream
Development
 Streams are classified as:
 Young
 Mature
 Old
 Name of the stage is not always related to the age
of the stream.
 Stage of development depends on slope of the
ground over which the stream flows.
Stages of Stream Development
 Young
Streams
 Streams that flow swiftly through steep
valleys
 May have whitewater rapids and
waterfalls
 Have high levels of energy
 Erodes the bottom faster than the sides
Stages of Stream Development
 Mature
Streams
 Very few rapids or waterfalls
 Erodes sides faster than the bottom
 Develops meanders
 Meanders are large curves in the river
 Form when the deepest part of the river is near
one side
 Deeper areas of the stream have water that flows faster
and erodes quicker
 Have broad, flat valley floors called
floodplains
Stages of Stream Development
 Old
Streams
 Have a broad, flat floodplain
 Usually form the trunks of watersheds
Too Much Water
 What happens
when water
from sudden
heavy rains or
melting of snow
enter a river
system?
 Water overflows the banks of the
river
 Flooding occurs
Too Much Water
 How can
flooding be
controlled?
 Dams can be built to regulate the flow
of water
 Levees (mounds of dirt) can be built
along the banks of the river
Too Much Water
 Catastrophic
Floods
 Very large floods that dramatically
change the surface of the Earth
 Ex:
 Lake Missoula
 covered much of western Montana
 Formed by natural ice dam
 When the ice melted, the dam broke releasing
large amounts of water that flooded Idaho and
eastern Washington
 The last flood occurred about 13,000 years ago
Deposition by Surface Water
 Deposition  Water in streams and rivers deposits
sediments when it looses energy
 Water often looses energy when flows it
from a steeper slope to a flatter surface or
when it flows into a lake or ocean
Deposition by Surface Water
 Deltas
and fans
 Delta
 Triangular, or fan-shaped, deposit that forms
as a river empties into a lake or ocean
 Alluvial fan
 Fan that forms as a river flows from a
mountain valley onto an open plain