Rivers have distinct features that change as they age. Young rivers in their upper stages have steep valleys and erode features like waterfalls through processes like abrasion. Mature rivers in their middle stages have less steep valleys and erode laterally. Old rivers in their lower stages have flatter valleys and deposit features like meanders and floodplains due to lower gradients. Rivers erode, transport, and deposit materials based on their volume and channel characteristics.

1. Natural Systems
RIVERS
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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
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–
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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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5. Dendritic drainage pattern
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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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8. RIVERS
RIVER PROCESSES
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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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15. RIVERS
The valley stages
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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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17. The life stages
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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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28. Spot the rivers features
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