Rivers CSEC Geography

Natural Systems

RIVERS

rm accounts ed ram@2013 rights

reserved

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)


reserved

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


reserved

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)


reserved

Dendritic drainage pattern rm accounts ed ram@2013 rights

reserved

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)


reserved

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)


reserved

RIVERS

RIVER PROCESSES


reserved

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).


reserved

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)


reserved

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)


reserved

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)


reserved

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


reserved


reserved

RIVERS

The valley stages


reserved

There are three life stages

• The Youthful stage (Torrent, Upper)

• The Mature stage (Middle)

• The Old Age stage (Lower)


reserved

The life stages


reserved

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


reserved


reserved

Erosional features (explain how each is formed)

• Potholes (circular depressions on the river bed)

• Plunge pools (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)

• rm accounts ed ram@2013 rights

reserved


reserved

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.


reserved


reserved

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.


reserved


reserved

Depositional features (explain how each is formed)

• Meanders (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)

• rm accounts ed ram@2013 rights

reserved


reserved

Spot the rivers features


reserved

Education

Rivers CSEC Geography