Chapter 6.1 and 6.2
The Distribution of Earth’s Water
The Water Cycle
Water Cycle Processes
 Evaporation – Liquid water changing into water vapor.
 Condensation – Water vapor turning into liquid water.
 Sublimation – Solid ice turning into water vapor.
 Deposition – Water vapor turning into solid ice.
 Freezing/melting – Liquid water into solid ice and solid
ice turning back into liquid water.
 Infiltration – water seeping and penetrating into the soil
to reach the aquifers (groundwater).
 Transpiration – water in the ground moves through plant
roots and leaves to evaporate from the plants.
River and Stream Characteristics
 Gradient – Gradient is how much a river or stream
drops over a certain distance. Usually expressed as
feet/per mile or meters/per kilometer.
 Discharge – Discharge is how much water (volume)
moves through the river in a certain amount of time.
Usually expressed in cubic feet/per second (CFS).
 Channel Shape and Texture – The types of material,
the depth of the channel and width of a channel all
affect the character of a river or stream.
Stream Gradient
 To calculate stream
gradient, subtract the
lower elevation from the
upper elevation.
 Divide the difference in
elevation from the
distance of the river.
 500 feet divided by 15
miles = 33.3 ft./mile
Stream Discharge
 To find the discharge of a stream, you multiply the
average depth by the average width of a stream. Then
you take that number and multiply it by the velocity.
Points of Interest on a Stream
 Headwaters or Source – A streams point of origin.
Where it started. Sometimes from a lake or glacier.
Often times streams start off as a small trickle of water
that comes from a spring out of the ground. No matter
where it starts, it is always at a higher elevation than
anywhere else along the entire stream.
 Ultimate Base Level – The end of all rivers. The
lowest point to which a stream can go. Sea level is the
ultimate base level of every stream.
Points of Interest on a Stream
 Temporary Base Levels – temporary base levels can
be any place along a stream where the water backs up
and loses energy to deposit its material.
 A temporary base level could be a large lake, a manmade dam or a beaver dam. Anything that temporarily
stops or obstructs the flow of water in the stream.
 Tributaries – Side channels that run into the main
channel. Tributaries increase the discharge of a
stream. As a stream travels to the ocean, more and
more tributaries flow into it to make it bigger.
Stream Profile
Stream Tributaries
How Rivers Change from the
Headwaters to the Base Level
 When rivers begin at their source, they have a high
gradient and so the erosion is more severe. This
causes a narrow v-shaped valley to occur.
 The force of gravity primarily cuts down.
 As rivers get closer to their base level, they start to lose
energy from gravity. Their gradient decreases
dramatically. As a result the river starts to widen and
the motion changes to a more side to side motion.
 This forms a meandering river in a wide floodplain.
V-Shaped Valley
Meandering River
How Rivers Change from the
Headwaters to the Base Level
 If a meander gets cut off from the main channel, a
horseshoe-shaped lake called an oxbow can form.
 The river keeps getting closer to base level. When this
happens, the river loses more of its energy and begins
to deposit sediment it has been carrying.
 Sometimes the river becomes braided because it is
choked with sediment.
 At the very end of the river, the river will widen
dramatically and form a pyramid or triangular shaped
feature known as a delta.
Oxbow Lakes
Braided Rivers
 Many Alaskan
rivers are braided
because of the
high amount of silt
produced from
melting glaciers in
the summertime.
River Deltas
This is a Delta on the Kenai River
Delta on the Nile River
A River System
Additional Features of Rivers
 Gravel Bars or Point Bars – Usually the velocity of a
stream is greatest on the outside bend of a river and
least on the inside bend of a river. Where the velocity
is the slowest, more deposition occurs. This is where
gravel bars or point bars form. Where the velocity is
the greatest, erosion and cut banks often form.
 Natural Levees – When streams and rivers flood their
banks, they deposit sediment along the side of the
river. This accumulation of sediment forms natural
levees that help contain rising flood waters.
River and Stream Features
Formation of a Natural Levee
Floods and Humans
 Historically humans have always lived along rivers.
Water is plentiful. The soils are rich in nutrients. The
agriculture is more suitable along the floodplain.
 The downside is that civilizations living on the
floodplain are vulnerable to floods.
 One way to prevent flood damage is by building
artificial levees. However, if the floods overtop the
levees (Hurricane Katrina), it can make the problem
even worse than it would have been without them.
Floods and Humans
 Building dams is another possible solution to
flooding.
 The problem with dams is that the sediment backs up
behind the dams causing flooding behind it.
 Also, by removing the sediment in the stream or river,
the river or stream increases its capacity to erode more
sediment downstream.
 Ultimately the best solution is to avoid living directly
on the floodplain itself. Living on the floodplain has
its benefits but it also has severe risks.
Drainage Basins
 A Drainage Basin is the
sum of all the area that
contributes water to a
major river or stream.
 It includes all the
tributaries, springs,
rivers, streams etc. in a
large area that drains
into a major river.