River Processes & Landforms

Chapter 5

River Processes

• Erosion removes material from a river bed making it deeper/wider

• These pebbles, sand, silt, etc. get transported downstream (river’s load)

• Deposition occurs after a river no longer has enough energy to carry the load and drops it on the river bed-boulders first, silt & mud last

How a River Transports

WORKSHEET

Factors Affecting River Work

• Velocity/energy-the faster the river the larger the material able to be transported

• After rain rivers may look brown due to suspension

Factors Affecting River Work

• Volume-the more water the greater the volume of the load

• Bedrock-harder rocks-i.e. granite- erode slowly, soft rocks-shale-erode easily & some rocks- i.e. limestone- can be dissolved completely

Deposition

• Occurs when rivers lose velocity– Decrease in the gradient– Decrease in river flow as

water drains after a heavy rain

– River meets the sea/lake– River flows slower on

the inside of bends

The River Channel

Upper Course of a River

Source• Where the river starts in a

highland or mountainous area

• Vertical erosion can be great in some areas and create gorges, canyons, potholes

• Potholes-smooth rounded hollows formed by stones trapped in the hollows of a river bed

Upper Course of a River

Rapids• Form where the water is

shallow and the river bed is rocky & irregular making the water rough

• Usually in steeper areas• Can make river travel

difficult unless white water rafting/kayaking

Upper Course of a RiverWaterfalls & Gorges

Victoria Falls Zambia & Zimbabwe

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Waterfalls & Gorges

Positives• Brings in tourists• Hydroelectricity

Negatives • Can cause navigation

problems, makes the river difficult to cross

Upper Course

Interlocking Spurs• Narrow valleys force the

river to create a winding path

Middle and Lower Courses

• As the river valley begins to widen and become less steep

• Begin to see more lateral (sideways) erosion

• Vertical erosion may stop completely by the time we reach the lower course

Meanders & Oxbows

Meanders & Oxbow Lakes

Floodplains & Levèes

• Flat land next to a river liable to flood

• Occasionally the river flows above the level of the surrounding plain but is enclosed by raised embankments called levèes

Floodplains & Levèes

Deltas

• Low-lying flat marshy land where a river meets a sea/lake

• Formed from a river with carrying a lot of sediments that meets a still sea/lake and the sediments build up

• May cause distributaries

Mississippi Delta, USA

Mahakam River, Borneo

The Long Profile of a River

• A line drawn from the source of the river to the mouth showing how the gradient changes

• Typically steep in the upper course and more gentle and smooth in the lower course

• Erosion & deposition remove irregularities in the profile making it smooth and concave

Long Profile

ACTIVITY

Living in River Flood Plains & Deltas

• Often densely populated• Offer flat land (easy to

build)• Fertile soils• River valleys are natural

route ways• Navigable rivers allow

transport & trade• Provide drinking water

and food source

Living in River Flood Plains & Deltas

• Tropics can suffer from diseases carried by insects i.e. malaria (mosquitoes) & sleeping sickness (tsetse flies)

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Flooding

• Discharge-the volume of water flowing down the river at any one time

• When the discharge can no longer be contained within the channel & overflows to the surrounding area it floods

• Dense population can make flooding severe

• When it rains, very little of it actually falls into the river, so where does the water come from?

Flooding

Activity

Factors Affecting Discharge• Rainfall• Relief

– Rainwater runs over steep slopes vs. infiltration on gentle

• Land Use• Weather Conditions

– Hi-temps reduce discharge

• Rock & Soil Type– Permeable vs. impermeable

Hydrographs

• Graph showing how a river responds to a storm

• Shows rainfall and discharge

Flood Prevention

Planting Vegetation• Planting vegetation (trees)

allows rainwater to be taken in by roots & go out through transpiration

• Acts like a sponge that releases water slowly so flood peaks are reduced

Flood Prevention

• Reservoirs can trap water and release it slowly

Flood PreventionStraightening the Channel

• Shortens the river and gets the water away faster.

Kissimmee River, Florida USA

Flood Prevention

Artificial Levèes• Increase the capacity of the channel• Usually banks are strengthened with concrete or stone so less

likely to break

Flood Prevention

Dredging the Channel• By making it deeper this

increases the capacity and makes it less likely to overflow

Flood Prevention

Bridge Design• Bridges with wide pillars and

walls on top act like dams which hold back water; modern bridges are slim and prevent this from happening

Flood PreventionWash Lands

• Control land on flood plains areas for recreation instead of residential to minimize damage

CAUSE & EFFECTS

Textbook Pg. 132-137 #7