10.3 – SOURCES
OF FRESH WATER
PG.376
OBJECTIVES
• Describe why run-off is important for rivers
• Describe how a small stream becomes a large river
• What is a drainage basin
• Describe the important and generation of an underground aquifer
• Describe the two different types of glaciers
KEY TERMS
• Crevasse
• Glaciers
• Gravity
• Ground Water
• Iceberg
INTRODUCTION
• Did you know about 1% of all of Earth’s freshwater supply is easy accessible
• Most of the water is trapped in ice, in Greenland and Antarctica, and not readily available for
human use.
• The freshwater that is found wherever water is falling as rain and snow runs off the land and is
collected in lakes, streams, rivers, and underground
INTRODUCTION
• What is ‘run-off’
• After a heavy rain shower, mini-rivers
wash over sidewalks, driveways and
roads. Where does the vast majority
of that water go?
• We call this flow run-off
• Some of that water is absorbed and
some evaporates but gravity will pull
the water in a certain direction
creating run-off
THE MIGHTY FRASER
• Did you know that the Fraser River drainage
basin covers an area equal to almost half the
entire province of British Columbia
• Snap your finger once, and imagine the water in
three Olympic pools moving. That is the
amount that moves in one second.
FACTORS AFFECTING RUN-OFF
• The amount of run-off is affected by six factors
1. The nature of the ground material
• Soil or rock
• precipitation falls on rock, as soils allow water to soak in
2. The amount of rain
• heavy rainfall saturates the ground so water can’t soak in
3. The length of time it rains
• long periods of rainfall saturate the ground so water can’t soak in
RUN OFF WILL INCREASE IF..
4. The slope of the land
• Downhill, flat: water can flow quickly down a steep slope, not having time to soak in
5. The amount of vegetation
• Logging, plants, shrubs: there is no vegetation, as plants help to absorb water and hold soil with their root
systems
6. The amount of development in the area
• Sewer vs ground: there is human development and no soils
HUMAN DEVELOPMENT OFTEN ALTERS
RUN-OFF
• How?
– Changing the direction of flow
– Farming
– Roads
– Forestry
SOURCES OF FRESHWATER
• There are 3 major sources of freshwater that we will look at a little bit closer
– Drainage Basins
– Ground Water
– Glaciers
DRAINAGE BASINS
• Drainage basins are large areas where surface water all
moves towards one main river
– Also known as watershed
– Run-off flows into streams and smaller rivers, which are
tributaries of large rivers, forming a branching system
– Think of the branches of a tree
– The rocky mountains are part of a long chain of mountains that
extend down the length of North America
– These mountains form the Continental Divide that separates
the pacific watersheds from the watersheds to the east of the
rocky mountains
GROUNDWATER
• Ground water is water that soaks into the
ground
– Rock/ground with good porosity allows
more water to enter
– More pores (spaces in the rock/soil), the
better the porosity
– An aquifer is a layer of porous rock that
allows ground water to flow, almost like a
river below the surface
GROUNDWATER
• Humans get fresh water from
– Reservoirs, natural or man-made
– Wells, drilled into aquifers down
to the water table, which is the
top level of the zone of saturation.
– The water table is very deep in
deserts, but near the surface in swamps
– The water table rises during wet seasons
GLACIERS
• Almost 66% of all fresh water on Earth is in glaciers
– Glaciers form from layers of snow falling over many years
– Glaciers melt slowly under their own weight, and slowly flow downhill
– Glaciers cover about 10% of the Earth’s surface
– Alpine glaciers (aka valley) found in mountains
– Continental glaciers (aka ice sheets) cover huge areas of land.
• Eg. Greenland and Antarctia
GLACIERS
Glaciers flow until one of two
things happen:
1. reach an ocean, where the
ice will spill over the edge
creating crevasses, that open
and icebergs fall off
2. reach an area where warm
temps allow as much melting
as re-freezing, or recede if
they melt faster than they can
freeze
VIDEOS
• TED-Ed
• NASA Vid
• Iceberg Alley
• JUMBO wild