2. Rivers
• Definition
– The natural flow of water from areas of
highland towards low-lying areas a long a
definite course (water course); and emptying itself
in
–
–
–
–
–
The Sea
Another river (tributary)
A Lake
A Swamp
A Swallow Hole (reemerge as springs)
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3. Some of the main features
Source
– The start of a river’s course
Mouth
– The point where a river flows into the sea
Channel
- the area along which the river flows
• Tributary
– a small river which flow into a larger one
• Confluence – the point where a tributary joins the main river
• Meander
- a bend in the river
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4. Stream Ordering
Streams are ordered from the number 1
onward i.e. there are:
– 1st order streams (the main river)
– 2nd order streams (a tributary which feeds the main river)
– 3rd order streams (a tributary which feeds another tributary
which in turn feeds the main river)
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6. The drainage pattern is
• the pattern created by a river and its tributaries
as seen from above.
• the pattern is based on a number of factors:
– The type and structure of the underlying rock
– The shape of the land mass
– The topography (layout of the land)
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7. Types of drainage patterns
• There are three types of drainage patterns :
– Radial
• (like the spokes of a bicycle wheel)
– Trellised
• (like the rectangular pattern created in block work)
– Dendritic
• (like the veins of a leaf)
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9. Energy and Friction
• The type of work a river performs over time
depends on
– the size and shape of its channel,
– the volume of water it carries, as well as
– the land surface over which it flows.
• These factors determine the river’s speed
(friction factor) and its power (energy factor).
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10. Rivers
• ERODE
– (wear away the earth’s surface due to its rapid speed and steep channel)
• TRANSPORT
– (remove eroded earth material due to loss of speed as channel widens and
gradient decreases)
• DEPOSIT
– (build up with eroded material due to its very slow speed and its relatively flat
and wide channel)
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11. River Erosion involves…
• Corrosion
(the water dissolves and removes soluble material in its path)
• Abrasion
(the water scours the bed and sides of its channel with its load)
• Corrasion
(
[see abrasion] the water uses the load to mechanically gouge of areas of the channel
• Hydraulic Action (the force of the water dislodges material from the channel)
• Attrition
(the material in load bumps into each other an disintegrate)
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)
12. River Transportation involves…
• Suspension (the lightest materials float along in the water’s currents)
• Traction
(
the heaviest materials bounce or roll along by the force of the water
• Saltation
(
some of the material hops and floats as the water moves downward
• Solution
(the dissolved minerals are carried along in the water itself)
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)
)
13. Deposition is a result of…
• Rivers drop off their load when
– Gradient or slope of the river bed decreases
– The channel widens or becomes shallow
– It enters an arid region and loses discharge and
volume
– It reaches a lake or sea, slowing it down
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16. There are three life stages
• The Youthful stage
(Torrent, Upper)
• The Mature stage
(Middle)
• The Old Age stage
(Lower)
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18. Characteristics of the upper stage
– Gradient averages 1 in 10
– Vertical corrasion is dominant
– Valley sides are steep with a narrow V-shaped cross
section
– The river flows around spurs or interlocking spurs
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20. Erosional features
• Potholes
• Plunge pools
(explain how each is formed)
(circular depressions on the river bed)
(a large (deep) depression at the foot of a waterfall)
• Waterfalls
(fast moving vertical flow of water from great height)
• Rapids
(a series of short, fast falls)
• Gorges
(steep sided, deep, narrow valleys)
•
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22. Characteristics of the middle stage
– Gradient is not as steep as the Youthful stage
– lateral erosion is dominant
– Valley sides are less steep with an open V-shaped
(closer to a U) cross section
– The river flows appear to meander across the channel
as the interlocking spurs are being cut away.
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24. Characteristics of the old age stage
– Gradient is rather low
– deposition is dominant
– Valley has a flat bedded U shaped (like a box) cross section
creating a wide flood plain.
– The river flows slowly as meanders are more pronounced.
– Silting and emerging vegetation hampers its flow in some areas.
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26. Depositional features
• Meanders
(explain how each is formed)
(a loop or definite bend in the river)
• Ox-bow lake (a crescent-shaped lake at the cut off of a meander’s neck)
• Deltas
(a flat piece of land built up by deposits at the river’s mouth)
• Flood plains
(a low-lying plain resulting from continuous overflowing of the river’s banks)
• Levees
(natural embankments built up by the river on the banks of the channel)
•
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