Humid geomorphic environment

1. Chapter Two
The Humid Geomorphic
Environment
GEE-421: GEOMORPHOLOGY-II
Presented by
Md. Nazir Hossain
Lecturer
Geography and Environment
Shahjalal University of Science & Technology
Sylhet-3114, Bangladesh
nazirswapon@gmail.com

2. Running Water and Streams
Running/flowing water is the result of net
precipitation = {Total precipitation (input) –
Evapotranspiration (output or loss) +
Infiltration}

3. Running Water
Running Water: Run-off, water flowing on the
surface of earth
Sources of Running Water
 Major sources: rain water & ice caps
 Minor sources: ground water, surface water
Classification of Run-off:
1. Immediate run-off: rain water
2. Delayed run-off: ice, glaciers, water fall, lake etc.

4. Stream & River
Stream: A stream is a body of water with a current, confined
within a bed and stream banks.
River:
 It is a channelized natural flow of water
 A large natural channel of water; a natural stream of water that
flows through land and empties into a body of water such as an
ocean or lake.
 A river is a natural watercourse usually freshwater, flowing
towards an ocean, a lake, a sea, or another river.
Stream is a small flowing water where as river is a collection of many
streams. A river is larger, deep, longer and wider where as a stream is a thin
shallow.

5. Terms
Source: origin of stream
Mouth: end at sea/lake
Estuary: wide mouth
Confluence: meeting point of two/more rivers
Doab: middle area of two rivers
River basin: an area of land drained by a river and its
tributaries
Water divide/shed

7. Origin and Evolution of Streams
Factors of river origin
Availability of sufficient water
Slope of land
Presence of soft rock
Type of climate

8. Classification of Streams/Rivers
1. Perennial stream : year round
2. Intermittent stream: seasonal
A perennial stream or perennial river is a stream or river
(channel) that has continuous flow in parts of its stream
bed all year round during years of normal rainfall.
An intermittent or seasonal stream is one that only flows
for part of the year.

9. Classification of Streams/Rivers (Cont…)
Davisian classification…
1. Youthful river: a river with a steep gradient that has very
few tributaries and flows quickly. Its channels erode deeper
rather than wider.
2. Mature river: A river with a gradient that is less steep than
those of youthful rivers and flows more slowly. A mature
river is fed by many tributaries and has more discharge than
a youthful river. Its channels erode wider rather than deeper.
3. Old river: a river with a low gradient and low erosive
energy. Old rivers are characterized by flood plains.

10. Stages of river
1. Upper/mountain stages
2. Middle/plain stages
3. Low/deltaic stages

11. Drainage system
A drainage system is the pattern formed by the
streams, rivers, and lakes in a particular drainage
basin.
They are governed by the topography of the land,
whether a particular region is dominated by hard or
soft rocks, and the gradient of the land.

12. Drainage Patterns
1. Dendritic drainage pattern
2. Parallel drainage pattern
3. Trellis drainage pattern
4. Rectangular drainage pattern
5. Radial drainage pattern
6. Deranged drainage pattern

13. 1. Dendritic drainage pattern
Dendritic drainage systems are the most
common form of drainage system.
In a dendritic system, there are many
contributing streams, which are then joined
together into the tributaries of the main river.
They develop where the river channel
follows the slope of the terrain.
Dendritic systems form in V-shaped valleys;
as a result, the rock types must be
impervious and non-porous.

14. 2. Parallel drainage pattern
A parallel drainage system is a
pattern of rivers caused by steep
slopes with some relief.
Because of the steep slopes, the
streams are swift and straight, with
very few tributaries, and all flow in
the same direction.
Parallel drainage patterns form
where there is a pronounced slope
to the surface.

15. 3. Trellis drainage pattern
The geometry of a trellis drainage
system is similar to that of a
common garden trellis used to
grow vines.
Trellis drainage is characteristic of
folded mountains, such as the
Appalachian Mountains in North
America.

16. 4. Rectangular drainage pattern
Rectangular drainage develops on
rocks that are of approximately
uniform resistance to erosion, but
which have two directions of
jointing at approximately right
angles.
The joints are usually less resistant
to erosion than the bulk rock and
streams eventually develop along
the joints.

17. 5. Radial drainage pattern
In a radial drainage system, the
streams radiate outwards from a
central high point.
Volcanoes usually display excellent
radial drainage.
Other geological features on which
radial drainage commonly develops
are domes and laccoliths.
On these features the drainage may
exhibit a combination of radial
patterns.

18. 6. Deranged drainage pattern
A deranged drainage system is a drainage system in
drainage basins where there is no coherent pattern to the
rivers and lakes.
It happens in areas where there has been much geological
disruption.

20. Channel Patterns
Major three types are…
1. Straight
 which are found in the most
tectonically active areas.
 This is more of a hypothetical end-
member, and are not often found in
nature.
 Straight-type channels can be found
at alluvial fans.

21. 2. Braided rivers
which form in (tectonically
active) areas that have a larger
sedimentary load than the
discharge of the river.
Channel Patterns

22. Channel Patterns
3. Meandering rivers,
which form a sinuous path in
a usually low-gradient plain
toward the end of a fluvial
system.

23. Process of Valley Development
Valley development depends on
Erosional power of main river and their tributaries
Structure and soil type of the area
Stages of river
 Upper/mountain stage
 Middle/Plain stage
 Lower/deltaic stage

24. River/Stream Processes
Erosional processes of a river conducted by
i. Hydraulic action
ii. Corrosion: erosion by small particles
iii. Attrition: the wearing away of river bed
iv. Solution

25. Erosional Landform Features
1. V-shaped valley
2. Gorge & Canyon
3. Rapid & Cascade
4. Waterfall
5. Pot hole
6. Meanders
7. River terraces

26. Erosional Landform features (Cont…)
1. V-shaped valley
 A river valley is usually V-shaped. The exact shape depends on
the characteristics of the stream flowing through it.
 V-Shaped valleys are found in the upper course of the river and
are a result of both erosion by the river and weathering.
 Rivers with steep gradients, as in mountain ranges, produce steep
walls and a bottom. Shallower slopes may produce broader and
gentler valleys.

27. 2. Gorge & Canyon
The word “canyon” is widely used in the United
States, and the term “gorge” is widely used in
Europe.
A canyon is a deep valley having steep sides, and a
gorge is a deep ravine with a river flowing through
it or a ravine without the river.
Canyons have been formed through long periods of
time and frequent erosion from a plateau level.
Gorges are mainly formed because of the flow of
water or lava. Like canyons, the walls of gorges are
also made of sandstone and granite.
Grand Canyon in Arizona and Kali Gandaki in the
Himalayas in Nepal.
Erosional Landform features (Cont…)

28. Erosional Landform features (Cont…)
3. Rapid & Cascade
Rapids are sections of a river where the river bed has a relatively steep
gradient, causing an increase in water velocity and turbulence.
Cascades is a small waterfall or a series of small waterfalls over steep rocks.
Rapids are hydrological features between a run (a smoothly flowing part of a
stream) and a cascade.
Rapids are characterised by the river becoming shallower with some rocks
exposed above the flow surface.
Rapid Cascade

29. Erosional landform features (Cont…)
4. Waterfall
 A waterfall is a place where water flows over a vertical drop in
the course of a stream or river.
 Waterfalls also occur where meltwater drops over the edge of a
ice shelf.
 Waterfalls are commonly formed when a river is young.
 Water passes over hard rock and erodes the softer rock below

30. Erosional Landform features (Cont…)
5. Pot hole
Potholes are cylindrical holes drilled into the bed of a river that
vary in depth & diameter from a few centimetres to several
metres.
They’re found in the upper course of a river where it has enough
potential energy to erode vertically.
It is also a circular hole in the bed of a river produced by
abrasion

31. Erosional Landform features (Cont…)
6. Meanders:
 A meander, in general, is a bend in a sinuous
watercourse or river.
 A meander forms when moving water in a stream
erodes the outer banks and widens its valley, and the
inner part of the river has less energy and deposits silt.

32. Erosional landform features (Cont…)
6. Measurement of Meanders:
The sinuosity of a river is a measurement of how much a river
varies from a straight line.
It’s a ratio between the channel length and displacement (straight
line distance) between two points in the river’s course:
Sinuosity Index = Channel Length / Displacement
A sinuosity of 1 (SI=1)
means that the channel is
perfectly straight.
A sinuosity greater than
1 (SI > 1) means that the
river meanders.

33. Erosional landform features (Cont…)
7. River terraces
 a terrace is a step-like landform.
 terrace consists of a flat or gently sloping
geomorphic surface, called a tread, that is typically
bounded one side by a steeper ascending slop.

34. River Transportation
Rivers transport material in four ways:
1. Solution - minerals are dissolved in the water and
carried along in solution. This typically occurs in areas
where the underlying bedrock is limestone.
2. Suspension - fine light material is carried along in the
water.
3. Saltation - small pebbles and stones are bounced
along the river bed.
4. Traction - large boulders and rocks are rolled along
the river bed.

36. Stream Load
 Stream load is a geologic term referring to the
solid matter carried by a stream.
 Erosion and bed shear stress continually remove
mineral material from the bed and banks of the
stream channel, adding this material to the regular
flow of water.

37. Sedimentation: Types of stream load
Stream load is broken into three types (Ritter, 2006).
1. Dissolved load: Dissolved matter is invisible, and is
transported in the form of chemical ions. All streams carry
some type of dissolved load.
2. Suspended load: Suspended load is composed of fine
sediment particles suspended and transported through the
stream. These materials are too large to be dissolved, but
too small to lie on the bed of the stream
3. Bed load: Bed load rolls slowly along the floor of the
stream.

38. Sedimentation: Types of stream load (Cont…)

39. Depositional Landform Features
1. Alluvial fan and cone
2. Bajada/Alluvial slope
3. Piedmont Alluvial plain
4. Incised meander
5. Floodplain
6. Horse-shoe/Ox-bow Lake
7. Sandbars
8. Natural levees
9. Back slope & Back swamp
10. Delta

40. Depositional Landform Features (Cont…)
1. Alluvial fan and cone
 Alluvial fan and cone: An alluvial
fan is a fan- or cone- shaped deposit
of sediment crossed and built up by
streams.
 Alluvial cone: An alluvial fan with
steep slopes

41. Depositional Landform Features (Cont…)
2. Bajada/Alluvial slope
 Bajada (Spanish “slope”) also spelled Bahada, broad slope of
debris spread along the lower slopes of mountains by
descending streams, usually found in arid or semiarid climates;
the term was adopted because of its use in the U.S. Southwest.
 A surface of alluvium which slopes down from mountainsides
and merges with the plain or broad valley floor.

42. Depositional Landform Features (Cont…)
3. Piedmont Alluvial plain
An alluvial plain is a largely flat landform created by the
deposition of sediment over a long period of time by one or
more rivers coming from highland regions, from which
alluvial soil forms.

43. Depositional Landform Features (Cont…)
4. Incised meander
a river meander which has been cut abnormally
deeply into the landscape because uplift of the land
has led to renewed downward erosion by the river.

44. Depositional Landform Features (Cont…)
5. Flood plain
 An area of low-lying ground adjacent to a river, formed
mainly of river sediments and subject to flooding
 A floodplain or flood plain is an area of land adjacent to a
stream or river that stretches from the banks of its channel
to the base of the enclosing valley walls and experiences
flooding during periods of high discharge.

45. Depositional Landform Features (Cont…)
6. Horse-shoe/Ox-bow Lake
 An oxbow lake is a U-shaped body of water that
forms when a wide meander from the main stem of a
river is cut off, creating a free-standing body of
water.
 This landform is so named for its distinctive curved
shape, resembling the bow pin of an oxbow.

46. Depositional Landform Features (Cont…)
7. Sandbars
 A sandbar or gravel bar, is a characteristically linear
landform completely within or extending into a body
of water.
 It is typically composed of sand, silt, and/or small
pebbles.

47. Depositional Landform Features (Cont…)
8. Natural levees
 A natural levee (or dyke), embankment, flood bank or stop
bank is an elongated naturally occurring ridge or wall,
which regulates water levels.
 It is usually earthen and often parallel to the course of a
river in its floodplain or along low-lying coastlines.

48. Depositional Landform Features (Cont…)
8. Natural levees

49. Depositional Landform Features (Cont…)
9. Back slope & Back Swamp/Marshes
 Back slope is the back part of a natural levee.
 Back swamp is the section of a floodplain where
deposits of fine silts and clays settle after a flood.
Back swamps usually lie behind a stream's natural
levees.
Back slope

50. Depositional Landform Features (Cont…)
10. Delta
 A river delta is a landform that forms at the mouth of a
river, where the river flows into an ocean, sea, estuary,
lake, or reservoir.
 Deltas form from deposition of sediment carried by a
river as the flow leaves its mouth.

51. World well-known deltas

52. Delta Types
Classification according to the shape of river delta
1. Arcuate type delta
2. Birds foot delta
3. Estuarine delta
4. Cuspate delta
5. Fan shaped delta

53. Delta Types (Cont…)
Arcuate type: like delta or bah (ব) in Bangla
 Arcuate deltas are triangular in
shape, like the Nile River's delta.
 This shape, resembling the Greek
alphabet's fourth letter, gave
deltas their name.
 Arcuate deltas usually have
smooth coastlines because of the
wave action and how they are
formed.

54. Delta Types (Cont…)
Birds foot Delta
 Bird-foot deltas have long finger-like projections that
reach out to the sea, like the Mississippi River's delta.
 The bird-foot delta is named for its long thin shape,
much like a bird's toe.
 These deltas might have broad, shallow shelves.

55. Delta Types (Cont…)
Estuarine Delta
Estuarine deltas form when a river flows into a large
estuary that will fill with sediment, as is the case
with France's Seine River.

56. Delta Types (Cont…)
Cuspate delta: when river elongated to sea
 Cuspate deltas extend to the sea as a V shape with long
curving sides, like the Tiber River's delta (Italy).
 The cuspate delta tends to form when one river or stream
empties into a flat coastline where it encounters a direct hit
from waves. This action forms its tooth-like shape.

57. Delta Types (Cont…)
Fan shaped delta: like alluvial fan

58. Flood
When the high flow of water overtops the natural or artificial
banks of a stream and inundates the adjacent areas is called flood.
In Bangladesh, the definition of flood appears differently. During
the rainy season when the water flow exceeds the holding capacity
of rivers, canals, beels, haors, low-lying areas it inundates the
whole area causing damage to crops, homesteads, roads and other
properties is known as flood.

59. Flood Prone Countries of the World
China
Bangladesh
India,
Indonesia,
Vietnam,
Cambodia,
Philippines,
Myanmar,
Brazil,
Netherlands,
Pakistan,
Eastern African countries

60. Flood in Bangladesh
Flood is common phenomena in Bangladesh.
Each year about 26,000 km2, (around 18%) of the country is
flooded.
During severe floods the affected area may exceed 75% of the
country, as was seen in 1998. This volume was 95% of the
total annual inflow.
The floods have caused devastation in Bangladesh throughout
history, especially during the years 1955, 1966, 1987, 1988
and 1998.
The 2007 and 2010 also affected a large portion of
Bangladesh.

61. Flooded area of Bangladesh in different year
Source: FFWC, 2009

62. Types of Floods
1. Monsoon flood: It is a seasonal flood, increases slowly
and decreases slowly, inundates vast areas and causes
huge losses to life and property.
2. Flash Flood: The flood is rapid characteristics. Water
increases and decreases suddenly, generally happen in the
valleys of the hilly areas.
3. Tidal flood: Storm surge flood is a coastal phenomenon
forced by cyclones hitting the coastline. Duration of this
flood is short; height is generally 3m to 6m but very
catastrophic in characteristics.

63. Floods
Monsoon flood
Flash Flood
Tidal flood

64. In general classification
Riverine flooding
Rain-fed flooding
Coastal flooding
Urban flooding: A few days to weeks
Types of floods (Cont…)

65. Flood Prone Area of Bangladesh

66. Causes of Flooding
 Physical causes of floods
 Low lying flat topography
 Being drainage outlet
 Excessive rainfall during monsoon
 Snow-melting in the Himalayas
 River siltation/landslides
 Synchronization of major river peaks and influences of one
river on the other
 Tidal and wind effects on slowing down the river outflow
(backwater effect)
 Being floodplain

67. Features of the Bangladesh Delta

68. The Brahmaputra, Ganges and Meghna basins

69. Causes of Flooding (Cont…)
 Human induced Causes of the Floods
 Increasing population pressure, unplanned settlements &
urbanization
 Construction of barrages and protective works
 Deforestation in the upper riverine countries.
 Infrastructure development without adequate drainage facilities.
 Lack of financial capital means.
 Poorly maintained embankments (levees) leak & collapse in times
of high discharge.
 Urbanization of the flood plain has increased magnitude &
frequency of floods.
 The building of dams in India

70. Common Consequences of Flooding
1. Economy
 Economic loss, e.g. house, crops, livestock,
 Reconstruction and rehabilitation cost
2. Environment
 Traffic: damages of roads, collapse of bridges or traffic
congestion,
 Damaging the farmland
3. Human lives
4. Diseases, e.g. fever, pneumonic plague, dermatopathia,
dysentery, common cold, break bone fever
5. Effect on food production
6. Livestock and Poultry

71. Common Consequences of Flooding

72. Common Consequences of Flooding (Cont…)
In terms of duration of effects…
1. Short-term Consequences: losses of lives, damages of
crops, property, livestock etc.
2. Long-term Consequences: famine due to damages of
food grain, environmental degradation, e.g. due to salinity
intrusion, river bank erosion, others.

73. Deadliest floods due to flood in the world
Death toll (Lac) Event Location Date
25–37 1931 China floods China 1931
9–20 1887 Yellow River (Huang He) flood China 1887
5–7 1938 Yellow River (Huang He) flood China 1938
2.3
Banqiao Dam failure, result of
Typhoon Nina
China 1975
2.3 Indian Ocean tsunami Indonesia 2004
1.45 1935 Yangtze river flood China 1935
1+ St. Felix's Flood, storm surge Netherlands 1530
1 Hanoi and Red River Delta flood
North
Vietnam
1971
1 1911 Yangtze river flood China 1911
Source: Myaux, J A et al., 1997

74. Positive effects of flooding
• Normal flood fertile agricultural land
• This deposition of silt also creates land upon which people
can live- for example the Ganges delta.
• Clean the environment by washing away the garbage, dust
and non-disposal materials.
• Increase waterway/navigation

75. Flood Management
A systematic and well-organized programme is
necessary against flood disaster.
Measures that can be adopted for flood damage
mitigation can be classified into two categories.
1. Structural measures
2. Non-structural measures

76. Structural Measures
Structural measures aim at protecting an area up to
certain level of flooding. It can be divided into five
categories:
i. Storage reservoir or basins to control overflow.
ii. Levees and floodwalls to confine floodwaters.
iii. Improvement of channel capacity.
iv. Flood diversion through bypasses.

77. Structural Measures
Examples of structural Measures:
• Embankments & Dykes
• Flood drainage & pumping system
• Flood control gates
• Flood proofing
• Channel improvement etc.
• Construction of flood shelters

78. Flood
control
measures

79. Embankments of Bangladesh Source: LGED, 2006

80. Non-structural Measures
Non-structural measures are aimed at reduction of loss due to flood
by administrative measures. Some of the non-structural measures
are:
Examples of Non-structural Measures
• Awareness building
• Early warning
• Legal framework
• Training & Education
• Incentives
• Relief and rehabilitation
• Legal framework
• Flood zonation & land management
Relief operation

81. Next Lecture
Third Chapter
81

82. Thanks To All
82