Channel Pattern (Fluvial Morphology).pdf

Hand Notes for Stream Channel Pattern (Fluvial Morphology) in the context of Bangladesh.

1. M J Ferdos
22
nd
Batch, MS-2022
GES, CU
STREAM CHANNEL PATTERN
Channel Pattern:
▪ Leopold and Wolman (1957): By channel pattern is meant the configuration of a river as
it would appear from an airplane.
▪ J. Chorley (1971) in ‘Introduction to Fluvial Process’: This is a trace of a channel in a
plane as shown on instance on vertical air photography or as represented on map.

Channel patterns are types of sedimentary deposits formed by streams and rivers. Collectively,
they are called fluvial deposits. Their shape and sediment characteristics are easily identified and
enormously complex. Understanding fluvial deposits is essential to economic geology because
many of these ancient deposits are a good source of petroleum.
Types of channel pattern:
1. Straight channel and channel pattern
2. Braided channel and channel pattern
3. Meandering channel and channel pattern
These are described Below:
Straight channel pattern: Straight channels are seldom straight for long distance and there is
usually an implication of the effect of initially steep slopes on homogenous rocks (Leopold et al.
1964).

2. M J Ferdos
22
nd
Batch, MS-2022
GES, CU
Characteristic of straight channel pattern there are given below.
• Straight are found in the most tectonically incised\active areas.
• Straight stream channels are rare.
• Where did the occur, the channel is usually controlled by a linear zone off weakness in
the underline rock, like a fault or joint system.
• Velocity is highest in the zone overlying the deepest part of the stream.
• Even the straight channel segment water flow in a sinuous fashion, with the deepest part
of the channel changing from near one bank to the other.
• In this area, sediment is transported readily resulting in pool.
• Where the velocity of the stream is low, sediment is deposited to from bars.
• The bank closest to the zone of highest velocity is usually eroded and result in a cut bank.
• Sinuosity is <1.5

Fig: straight channel pattern
Braided channel pattern: Braided channel is the one that has developed in several channels that
successfully meet and re-divided (Leopold et al., 1964). Braided rivers consist of two or more
hannel divided by bars or islands, lead one channel being dominated (David, 1984). For example,
Yamuna River.

3. M J Ferdos
22
nd
Batch, MS-2022
GES, CU
A braided river differs from a meandering river, which has a single sinuous channel. It is also
distinct from an anastomosing river. Anastomosing rivers are like braided rivers in that they
consist of multiple interweaving channels. However, anastomosing rivers consist of semi-
permanent channels which are separated by floodplain rather than channel bars. These channels
may themselves be braided. Braided channel low gradient end of river.

Meandering channel pattern: A bend or curve during a river is called a meander. A river will
bend by any kind of obstacle such as hard rock or pebble. Larger rivers have larger meanders and
vice versa.
Because of the velocity structure of a stream and especially in stream flowing over low gradient
with easily eroded bank straight channel will eventually be eroded into meandering channel.

Meander development & growth:
 Meandering thalweg(watercourse) along insufficient to generate meandering channel.
 Requires lateral erosion and depositions.
 Requires local rather than widespread bank erosion.
 Requires helical flow transporting from meander bend and depositing it in riffle or next
pint bar.

4. M J Ferdos
22
nd
Batch, MS-2022
GES, CU
Characteristic of meandering channel pattern:
1. In this channel erosion will take place on the outer parts of the meander bends where the
velocity of the stream is heights.
2. Sediment deposition will occur along the inner meander bends where the velocity is low.
3. Because meandering streams are continually eroded on the outer meander bends and
depositing sediment along the inner meander bends, meandering stream channels tend to
migrate back to forth across their flood plain.
4. Requires lateral erosion and deposition to from
5. Meandering channel is characterized by turbulent flow, velocity varies both horizontal and
vertically across the channel. It transports the materials both as bed load and wash load.
6. Features of this type of channel includes channel lag, point bar, over bank deposit, natura
leaves, flood plain deposit ox-bow lake etc.

Example of meandering channel: meandering river in northern Owens valley; Sacramento River,
California; Ob River, west Siberia.
Difference between Drainage Pattern and Channel Pattern:
Topic Channel Pattern Drainage Pattern
Definition
Configuration of a river or stream
channel.
Configuration of drainage basin.
Area
Association
Not associated with area. Can be
defined with any unrelated channel.
Associated with area that has a
common precipitation outlet point.
Types Braided, straight, meandering etc.
Dendritic, parallel, Radial, Annular,
Anastomotic, centripetal etc.

5. M J Ferdos
22
nd
Batch, MS-2022
GES, CU
Outlet It does not have single outlet. It has a single outlet.
Division It meets with branches and divides. Does not divide.
Branches Has branches called tributaries. Does not have tributaries.
Accumulation
Sometimes, channels work as a unit of
drainage pattern.
Several channels can be accumulated
in a drainage pattern.

Identification Characteristics of Yamuna River:
• According to Sharma and Kansal (2013), The Yamuna River is dissected at 5 barrages
during its course i.e. at Dak Patthar (near Uttaranchal); at Hathnikund (near Haryana); at
Wazirabad (near Delhi), at Okhla (near Delhi); and at Mathura (near Uttarpradesh). It has
other barrages and small rocky formations too.
• Apart from that, in Bangladesh, the Yamuna River has several barrages and islands at
Manikganj, Tangail, Jamalpuretc. This is basic feature of a braided channel according to
Leopold et al. (1964).
• There are several sub-flows of Yamuna such as- Chambal, Sind, Betwa, Ken, Hindan,
Rind, Senger, Varuna etc. Having sub-flow is a feature of braided river channel according
to David (1984).
• According to Chaudhary (2016), there is sedimentation and TOC (total carbonic organ) in
the Yamuna River that influences the river depth to become shallower. It’s also a feature
of braided river channel.
From the above characteristics mentioned by different authors, it can be concluded that the
Yamuna River is a braided river channel.
The Stream Cycle
As a river erodes its banks and bed, it changes the landforms it passes though and alters its own
course. The development of a river system is divided into three stages: Youthful, Mature, Old
Delta stream enters a standing body of water.
Usually happens at deltas. Velocity drops and sediment is deposited. They build outward from
coastline. Can only survive in low current and velocity.

6. M J Ferdos
22
nd
Batch, MS-2022
GES, CU
Identification of Tista River with Characteristics:
Tista River an important river of the northern region of Bangladesh. It enters Bangladesh at the
Kharibari border of Nilphamari district. It relates to Yamuna.
This river falls under the category of straight channel pattern due to the following features-
• This river flows from Chatnai to Niphamari, Rangpur and Gaibandha and meets with
Yamuna River; in this flowing way, it almost remains straight but twisted at some areas.
This is the feature of a straight channel.
• Tista river has carved out ravines and gorges in Sikkim meandering; consequently, it is
surrounded by rocky band formed near ravines and meanderings; which is a feature of
straight channel.
• Due to the existence of gorges (canyon) it has steep slopes at some points; it is also an
important feature of straight channel.