River Landform

River Landform

1. Rivers: Profiles &
Landforms
Pankaj Kumar Singh

2. River Profile
Source
of river
Upper
Course
Middle
Course
Lower
Course
Cross sectional Profile – Width of River
Longitudinal Profile - From Source to mouth
( Length of River )

3. River
system
Headwat
er
Tributaries
Trunk
stream
Distributarie
s

4. Upper Course - Channel features
•River channel is rocky.
•Covered with various shapes and sizes
of boulder.
•Discharge is low.
•Under flood conditions rivers energy is
expended on vertical erosion with
hydraulic action and corrosion processes
at work.
•Potholes may form.

5. Vertical erosion

6. Pothole formation

7. Upper Course - Valley features
•Valley sides are steep and form a ‘V’ shaped
cross section.
•Interlocking spurs.
V shaped valley
Steep sides
Zig-zag bends
(interlocking
spurs)

8. V – shaped valley
Form due to a combination of
the following processes:
Vertical erosion by the river
itself.
Physical weathering (eg:
frost action) which provides
debris to move down slope.
Mass movement (inc: soil
creep & landslides) to move
debris down slope.

9. Interlocking
spurs
River flows around
interlocking spurs

10. Upper Course – Long Profile
•Generally the gradient is steep and the
profile is uneven, particularly where
waterfalls and rapids form.

11. Waterfall formation
Hard Rock – Lava
Soft Rock – Sandstone or Conglomerates
Soft rock is easy to
erode, but the hard rock
is resistant.
So over time a ledge
develops.

12. Waterfall formation
The water rushes over the
ledge and erodes a plunge
pool by abrasion and
hydraulic action.
Hard Rock – Lava
Soft Rock – Sandstone or Conglomerates

13. Waterfall formation
The ledge collapses into
the plunge pool, where
the debris helps to
speed up the erosion.
Hard Rock – Lava
Soft Rock – Sandstone or Conglomerates

14. Waterfall formation
The process is repeated
and the waterfall
gradually retreats
upstream, carving out a
gorge.
Hard Rock – Lava
Soft Rock – Sandstone or Conglomerates

16. PLUNGE
POOL
UNDERCUTTING
OF SOFT ROCK
OVERHANG
WATERFALL
RETREATS . .
UPSTREAM . .

17. Formation of rapids
Resistant rock Less Resistant Rock

18. Middle Course - Channel features

19. Middle Course - Valley features
•River erosional energy is now increasingly
expended horizontally rather than vertically.
•Lateral erosion by the river’s meanders
broadens the valley floor into a narrow flood
plain.
•Meanders gradually shift their course
downstream.

20. Middle Course 2

21. Meanders
A meander starts as a slight bend:
Water flows faster on the outer curve of
the bend (more energy), and slowest on the
inner curve (less energy).
So the outer bank gets eroded while
material is deposited at the inner bank.
Over time the outer bank gets worn away
(river cliff) and the inner one builds up
(river beach). The bend grows into a
meander.

22. Meanders
(refer to previous notes and diagrams)
•Alternating series of irregularities develop
•Pools – deeper stretches of slow moving water
•Riffles – shallower section of faster flow,
flowing above coarser material
•River develops a winding or sinuous course
•Faster flow on outer bend results in erosion
and formation of River Cliff
•Slower flow on inside of bend results in
deposition and formation of Slip-off Slope

23. Meanders
•Meanders develop and
migrate laterally and
downstream
•Turbulance flow further
assists meander
formation and transports
sediment from river cliff to
the slip-off slope on the
inside of the next bend.

24. MEANDERS
Flood plain
Meanders
Most erosion
on the outside
of the bend .. Fastest flow
Possible break
through point
Possible
ox-bow
lake

25. Meanders

26. Lower Course - Channel features
•The channel is now at its broadest and deepest.
•Bedload is carried entirely in suspension and is
solution.
•Deposition now dominates – particularly during
floods.
•Erosion also occurs – in the formation of
meanders

27. Lower Course – Valley features
•Thanks to lateral erosion the valley sides
may now be several kilometres away.
•Typically it may also contain the following
features:
Floodplain & natural levées
Braided channels
Meanders
Oxbow lakes
Estuaries and deltas

28. Lower Course

29. Gentle valley sides
Flat floodplain
Layers of silt
Deposited during floods
Coarse material
Forms natural
levees
River is actually flowing above
The floodplain !!
Levees is often
artificially
strengthened

30. Levee
s

31. Oxbow
lakes

32. Braided channels
•Formed by the choking of the main
channel by the deposition of a
considerable amounts of the river load.
•The channel splits into several smaller
channels which flow around fresh ‘islands’
of deposited material before rejoining.

33. Braided channels

34. Braided channels

35. Oxbow lakes

37. NARROW MEANDER NECK
FUTURE
OX-BOW LAKE