10.3 – SOURCES OF FRESH WATER

PG . 3 7 6

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