Use of Asymmetry Indices and Stability Indices for ......well as dynamism of channel configuration...

Journal of Engineering, Computers & Applied Sciences (JEC&AS) ISSN No: 2319-5604 Volume 2, No.1, January 2013 _________________________________________________________________________________

www.borjournals.com Blue Ocean Research Journals 24

Use of Asymmetry Indices and Stability Indices for

Assessing Channel Dynamics: A Study on Kuya River,

Eastern India

Priyanka Das, Research Scholar, Deptt. of Geography, Visva-Bharati, Santiniketan, West Bengal

Surajit Let, Research Scholar, Deptt. of Geography, Visva-Bharati, Santiniketan, West Bengal

Dr. Swades Pal, Deptt. of Geography, University of Gour Banga, West Bengal

ABSTRACT This paper aims to examine the nature of width, depth and configuration distribution along Kuya River and

their temporal directionality of changes. It also pays attention to prepare some simplified indices regarding

basin asymmetry, channel asymmetry and river bank stability and to explain the nature of basin and channel

asymmetry and river bank stability using those constructed indices. Irregular channel configuration, fast rate

channel widening in upper and middle reaches reflect the human interference. Basin asymmetry index or Areal

asymmetry index (BAI or AAI) is only 0.39 which speaks that basin is asymmetric and basin tiltation is toward

right catchment but channel or thalweg asymmetry index (CAI or TAI) says that it is reverse to basin asymmetry

on an average. Bank stability is fairly poor for the entire channel. River channel asymmetry and bank stability

are linked with total width pattern of the channel.

Keywords: Basin Asymmetry, Channel Asymmetry, Bank stability, Channel Widening, Temporal Width and

Depth Fluctuation, Channel Configuration Dynamics, Causes of Asymmetry.

1.1 Introduction Basin asymmetry is defined as the proportion of

area in two sides of the main river and thalweg

asymmetry is defined as the distribution of width in

two sides of the thalweg. These indicators clearly

reveal the tilting tendency of the basin and channel

(Pal, 2011). Weighted asymmetry index means

after measuring asymmetry for some selected

parameters, logical weightage is provided to each

one and thereby the level of asymmetry is

measured. This technique is more down to earth for

assessing basin asymmetry. According to the nature

of width, depth, discharge, velocity, sediment load,

slope of the land; the channel configuration of the

river is characterized (Leopold and Maddock,

1953; Mukhopadhyay, 1995. Although all these

said parameters are natural but people are

frequently tampering those parameters and often

reshape the channel configuration. In natural

condition the shape of the channel configuration is

quite steep and narrow in upper catchment and

gradually it becomes wider and flatter towards its

confluence. Presently, most of the river is under the

domain of human cultivation in terms of building

of barrage, dam across river, embankment along

river, diversion of water from the main river

through irrigation projects. These again are

regulating the behaviour of erosion, deposition as

well as dynamism of channel configuration in

different parts of the channel. So along with

structural and lithological control on channel

configuration, channel asymmetry, human

activities play vital role to determine the nature of

asymmetry and dynamics. This paper is more

attentative to formulate some simplified techniques

to measure the degree of basin asymmetry, channel

asymmetry of a river rather than to find out the real

world causes for such asymmetry. It has also

stressed on the stability of the bank with proper

equation because stability of bank is rigorously

related with channel width in particular and

channel configuration in general.

1.2 Study Area Kuya River is a well known name in the riverine

landscape of Eastern India. Taking start from a

large pond of Khajuri village, Jharkhand and

flowing S-E direction over Birbhum and

Murshidabad districts of West Bengal it has joined

the Babla River near Nalghosha village of

Murshidabad district. Total length of the river is

176.4 km. The basin area can be delimited by

23º26′18″ North to 23º56′30″ North latitude and

87º13′ East to 88º09′30″ East longitudes covering

an area of 1555.2sq.km. Total length of the river is

176.4 km. About 24.64 km. is semi permanent.

Total length of its main tributary- Brakeswar (Twin

river of Kopai: Kopai and Brakeswar together have

made Kuya river) is 82.98 km. out of which 10.57

km. is semi permanent and rest portion is

permanent. The lower segment of Kuya river has

embanked to restrict the over spilling tendency of

the river. Canal network in name of Kopai South

Main Canal, Mayurakshi Canal System are existing

in this basin. Tilpara barrage supplies water to this

channel through these canal systems. Kultore

barrage has built up over this river for irrigation

purpose. It retains water except peak monsoon



period. Twenty seven brick kiln industries have

found along side this river.

1.3 Materials and Methods Channel profiles have made through direct field

measurement, previous status of channel

configuration have been prepared with the help of

site specific bank dwellers and some previous

literatures belongs to Dr. Sutapa Mukhopadhyay.

Dumpy level has used to prepare the cross profiles.

The major formulas have prepared and used for this

basin are basically three types.

A. Basin Asymmetry

i. Basin Asymmetry Index (BAI) or Areal

Asymetry Index (AAI)

ii. Stream Length Asymmetry Index (LAI)

iii. Stream Number Asymmetry Index

(NAI)

iv. Relative Relief Asymmetry Index (RAI)

v. Composite Asymmetry Index (CAI)

vi. Weighted Asymmetry Index (WAI)

B. Channel Asymmetry

C. Stability Indices

i. Site Specific Stability Index (SSI)

ii. Average Stability Index (ASI)

Basin Asymmetry Index (BAI) or Areal

Asymmetry Index: AlAaI

Am Al = One side of the

main stream having less area; Am = One side of

the main stream having more area

Length Asymmetry Index: L l

LAIL m

Lµl = One

side of the main stream having less total stream

length; Lµm = One side of the main stream having

more total stream length

Stream Number Asymmetry Index: N lNAI

N m

Nµl = One side of the main stream having less total

number of stream; Nµm = One side of the main

stream having more total stream number

Relative Relief Asymmetry Index: RRl

RRAIRRm

RRl = One side of the main stream having less

relative relief; RRm = One side of the main stream

having more relative relief

Composite Asymmetric Index (CAI):

1

n

i

PAI

CAIN

PAI = Parameter Specific

Asymmetry Index; N = Number of parameters

1

n

i

Al N l SL l RRlPAI

Am N m SL m RRm

PAI= Parameter Specific Asymmetry Index

For preparing composite and weighted asymmetry

indices four relevant and measurable absolute

parameters have selected namely area, stream

number, stream length and relative relief from left

and right side catchments of the main stream.

1

*n

i

WAI Wi PAI WAI= Weighted

Asymmetry Index; Wi= Weight of ith parameter

CAI and WAI values range from 0-1. „0‟ means

highly asymmetry and „1‟ means symmetry.

PAI value also ranges from 0-1. „0‟ means highly

asymmetry and „1‟ means symmetry.

Channel asymmetry index mi

ma

CWCAI

CW

minmiCW average imumwidth

maxmaCW average imumwidth

Site Specific Stability Index (SSI) has used to

measure the river bank stability of in different

selected sites along a channel.

1SSI

Rcw SSI= Site specific stability index for

channel widening; Rcw= Rate of channel

widening

Average Stability Index (ASI) has calculated to

estimate river bank stability for entire channel.

1

1( ) /

n

i

ASI nRcw

ASI= Average stability index

for channel widening for entire channel; n=

Number of sites

SSI and ASI range from 0-1. Value nearer to „0‟

means less stability; „1‟ means high stability of the

bank. If the minimum value is less than 1m., all

widening values shuld be converted into smaller

units like meter to cm.

Correlation, regresion and least square methods

have used to perform inter component relation,

trend of change with degree etc.



Fig. 1 Reference map

1.4 Results and Analysis 1.4.1 Width Distribution in Channel

Configuration

In contrast to normal width pattern, in case of Kuya

river, the width of river has declined downstream.

The width of the channel, in most of the sites, is

more toward right which indicates tilting tendency

of the channel toward left.

Fig. 2 Width Distribution and Dynamics

Fig. 3 Wetted Width Distribution and Dynamics

0

30

60

90

120

150

180

0

30

60

90

120

150

180

0 55055 110110

Post Monsoon Monsoon

Len

gth

in

km

.

Source

Mouth

Wetted Width in m.

Legend(Wetted Width)

2011

2010



Wetted width distribution shows normally a good

parity with channel width distribution. But

temporal asymmetry of wetted width reflects the

hydrological consistencies and stability of the

channel. There are however significant variation in

wetted width distribution in monsoon and post

monsoon period (Fig. 3). In the upper and middle

course, wetted width almost doubles during

monsoon but in the lower course slight increase in

wetted width reveals the supply of water from

underground sources and flat slope, steep wall

channel.

1.4.2 Depth Distribution in Channel

Configuration

In general channel depth decreases downstream.

But, reverse result is found in case of Kuya river

because depth of channel has increased

downstream (Fig. 4). Increase of discharge volume

toward downstream, supply of water by Brakeswar

river, narrow width etc., accelerate channel

deepening and flow momentum. Moreover, the

fragile bed rock also responsible for fast channel

deepening.

Maximum and average depth variation has no

definite trend from source region to mouth of the

main channel. It can fairly be said that the variation

is to some extent less in the middle catchment.

Fig .4 Depth Distributions

1.4.3 Basin and Channel Assymetry Basin asymmetry index (BAI) or Areal Asymmetry

Index (AAI) for Kuya river basin is 0.39. Basin has

lopsided tendency toward right side as the

proportion of area in the left side is far more than

right side. All individual parameter specific

Asymmetry Index (PAI) shows the same tendency

as like areal asymmetry. Asymmetry regarding

number of stream and stream length are extremely

high in this basin. Stream length asymmetry is

0.223 indicates out of total stream diversity of the

basin, left side catchment explains 78% and right

side explains only 22%. Parameter specific

Asymmetry Index is 1 means there is no disparaty

of different parameter status between left and right

catchment of the basin. Spatial narrownwss has

largely leaded to be small values in the right side

catchment of the basin. Composite asymmetry

index of the basin is 0.439 means the basin is on an

average 56% away from achieving accodant

distribution of the selected parameters as a whole

between left and right catchment. Arbitrary weight

has been assigned to the individul parameter as per

logical understanding and thereby weighted

asymmetry index has been calculated. WAI value

0.4102 also indicates high level asymmetry in the

basin.

Channel asymmetry index (CAI) = 0.552 (average

right width is 33.48m. and average left width from

thalweg is 18.48m.). So, channel is tilted toward

left.

There is a contrasting tendency of basin and

channel tiltation. From topographical point of view,

it is expected that thalweg should be more toward

right part of the channel as the course is convex

toward right hand catchment. The basin is tilting

toward right but channel width is tilting toward left.

So, topogrphical controls on river channel

allignment is very prominent in Kuya river course

but hydrological pattern is tending to rest at along

the toe of the right slope catchment. In this context,

it is mentionable that master stram of this basin

Mayurakshi, one of the major tributaries of

Myurkshi (Dwarka) show the symmetric pattern of

river course alignment in a basin and thalweg

distribution within channel (Pal, 2011; Pal & Let,

2011).

0 60 120 180Distance in km.

Dep

th in

m.

Surface

1

2

3

4

5

6

(0)

ConfluenceSource

1

2

3

4

56 7

8

9

11

12

14

15

N.B. : No. indicates Working Sites

Average Depth

10

7

Average ofMaximum DepthReferences

(Depth)

Maximum

Average



Table 1: Some Assymetry Indices

Parameters Left Right PAI CAI Wi WAI= Wi*PAI WAI= ∑(Wi*PAI)

Number of stream 524 117 0.223

0.439

0.2 0.0446

0.4102 Length 867 324 0.373 0.2 0.0746

Avg. RR 11 8.5 0.77 0.15 0.1155

Area 948.72 606.52 0.39 0.45 0.1755

1.4.4 Rate of Channel Widening The channel widening rate is Kukutia, just at the

downstream of Kultore barrage due to the effect of

irregular discharges from barrage and it is very less

at confluence. From source to mouth there is

decellerating trend of channel widening (regression

coefficient value is 0.225) (Fig. 5) which is reverse

to the normal behaviour of the channel.

In lower reach of the channel, the rate of channel

widening is relatively low because on this portion,

there is less provision for brick kiln industries, less

effect of dam or barrage. The kind of erosion,

which is happening, is either due to misfit

agricultural land use or due to natural process of

widening. Possibility of river bed aggradation is

not strongly high because of the greater supply of

water from underground and canals. In lower

course of the river the channel wall is steep and

irregularities within channel are very less.

1.4.5 River Bank Stability Site specific stability index shows that no strong

directionality of bank stability is found from source

region to confluence. But trend value (R2=0.108)

analysis reveals that marginally but clearly the site

specific stability index increases downstream

indicating rising bank stability or less instability of

bank. Clay soil composition, smooth spilling

facilities of water, less interference of human being

on channel etc. are some root cause behind such

unexpectedly reverse results. High discharge

volume, velocity do not facilitate to channel bed

aggradation. Due to fragile laterite soil composition

of the river bank in the middle reach of Kuya river

the rate of bank stability is poor. This kind of

tendency is also found in river Mayurakshi and

Dwarka (Pal, 2011; Pal, 2012). Over all bank

stability is poor (0.208) for Kuya river channel

which indicates greater potentiaality of chaannel

widening in near future.

Table 2: Rate of Channel Widening and Index of River Bank Stability

Sites

Bank to Bank

Distance

Total

Widening(m.)

Rate of

widening

(m./Year)

Site specific stability

index for Channel

Widening

Average

stability

index for

Channel

Widening 2011 1980

Khajuri 25 19.5 5.5 0.177 0.181818

0.208589

Panchmohali 10.13 8.2 1.93 0.062 0.518135

Kukutia 123.8 78.45 45.35 1.463 0.022051

Hetampur 67.56 43.42 24.14 0.779 0.041425

Korkori 110.2 86.3 23.9 0.771 0.041841

Geltia 57.9 48.84 9.06 0.292 0.110375

Kamalakantapur 39.09 23.45 15.64 0.505 0.063939

Sehala 64.96 53.87 11.09 0.358 0.090171

Milanpur 1 19 16.3 2.7 0.087 0.37037

Milanpur 2 39.3 33.74 5.56 0.179 0.179856

Miriti 36.7 34.22 2.48 0.08 0.403226

Mamadpur 31.75 26.85 4.9 0.158 0.204082

Sabitrinagar 57.5 51.78 5.72 0.185 0.174825

Nalghosa 45.5 43.57 1.93 0.062 0.518135



Fig. 5 Channel Widening Rates in Diffferent Sites

1.4.6 Temporal Dynamics of Channel

Configuration In this section, comparision of chanel configuration

between 1980 and 2011 has done in different sites

to assess the nature of temporal changes.

In Korkori, previous channel was mechanically

shifted toward right for rail routing. Since that

period channel widening rate has started with very

fast rate and river has distinct tendency to shift

toward its palaeo course. Present scenario shows

that the previous deep right side portion of channel

is replaced by aggradation and shallower left side is

substituted by deeper channel.

In Kukutia, just at the downstream of Kultore

barrage, the width of the channel is as maximum as

123 m. Sudden flash dischrge from Kultore barage,

scooping of soil from the right bank of this site

have energized the fast rate channel widening.

In Kamalakantapur the rate of channel widening is

quite natural. In this place river has one palaeo

channel to its right hand side. With growing

deposition at the right hand side, the river has

started to shift left ward and now steady bank

erosion is going on towards the village,

Kamalakantapur.

At Hetampur, the rate of channel widening is

significantly high because the deserted brick kiln

industries, have paved the channel widening rate.

Possibilities for further channel widening in very

near future is also clear because present brick kiln

industry scooping huge amount of soil from river

bank. Waste building materials and eroded

materials have to some extent elevated the channel

bed level and forced channel to wide out.

At Mamadpur, there is a distinct channel

bifurcation. Previously river was flowing through

left channel but now main flow shifted to right

hand side. This present course is both narrow and

less deep. Fast channel aggradation in the previous

channel has shifted this flow. Deposition rate is

faster in this part because the flowing speed is to

some extent decelerated by the resistance offered

by one bridge just ahead.

At Geltia, there is also tendency of channel

widening and bed level rise. Channel is shifting

towards left and depth of this part has also slightly

increased in comparison to previous situation.

From all the said configuration it is proved that

within a single cross section all parts either has not

aggraded or degraded but on an average the

tendency of river bed aggradations and width

sprawling is more common all through the channel.

It is also noticed that when river has shifted from

its previous course, the current course is quite

narrower than previous.

y = -0.0451x + 0.7065

R² = 0.2251

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

Val

ue

in m

.

Name of the sites

Pattern of Channel Widening (Kuya River)



Fig. 6 Channel Configuration Fig. 7 Channel Configuration



1.4.7 Causes of Asymmetry and River

Bank Instability Asymmetry appears to provide an important link

between cross-sectional and plan form adjustment

(Kington, 1982). River bank instability is a natural

phenomena but it becomes thought provoking

when it is extremely irregular and arrhythmic. He

also established five stages models for asymmetry

appearance in channel. Channel asymmetry is

linked with bed forms, bed load characters etc.

(Milne, 1983). Knighton in his “Asymmetry of

River Channel Cross-Sections: Part I. Mode of

Development And Local Variation” has established

that channel width variation is not linked with

channel configuration but present author identified

that with increase of width level of asymmetry is

inflating specially in this river. It is also found that

degree of river bank stability negatively linked with

total width of the river. It indicates wide channel

cross section indicates upcoming bank instability

(R2=0.345). Human intervention aiming to tame

river strongly influences the level of asymmetry.

Slope and lithological structure largely control over

basin asymmetry. Generally steep slope with

muddy composition is susceptible for greater river

bank instability but in the downstream this kind of

slope pattern is noticed but the degree of bank

instability is not expectedly high. Earlier it is

mentioned that poor laterite soil composition in the

middle catchment encourages for such kind of bank

instability. Channel asymmetry strongly controls

hydraulic flow axis, nature of bank erosion, nature

of flood spilling, potential river bank instability etc.

Flood condition of any flood plain often becomes a



function of channel asymmetry (Shetye & Gouveia,

1991).

1.5 Conclusion In fine it can be said that the indices have

formulated those are compatible to present the

relative status of the situation in very liquid

fashion. The scale of the indices which range from

0 – 1 is also fruitful to understand the relative

status of actual reality. In upper and middle reaches

of the channel, widening pattern is high and

channel configuration is much irregular. But in

lower reach of the river, the channel widening

pattern is low and channel configuration is regular.

River bank stability is poor due poor soil

composition, seasonal hydrological fury within

channel, constant human interference etc. Basin

and channel asymmetry are found in contrasting

direction which is not normal behaviour. River

bank instability can partially be marginalized

controlling human interference.

References [1] Knighton, A.D. (1982): Asymmetry Of River

Channel Cross-Sections: Part II. Mode of

Development And Local Variation; Earth

Surface Processes and Landforms, Vol. 7,

Issue 2, pp. 117-131

[2] Knighton, A.D. (1982): Asymmetry Of River

Channel Cross-Sections: Part I. Mode of

Development And Local Variation; Earth

Surface Processes and Landforms, Vol. 6,

Issue 1.

[3] Leopold, L.B. and T. Maddock, (1953): The

hydraulic geometry of stream channels and

some physiographic implications, USGS

Professional Paper 252, pp. 1-57.

[4] Let, S. & Pal, S. (2011): Human Impact and

Channel Hydrological Modification: A Study

on Dwarka River of Eastern India,

International Proceedings of Integrated

Scientific, Engenieering & Management

Society, Thailand, pp. 261-267.

[5] Milne, J.A. (1983): Variation in Cross-

Sectional Asymmetry of Coarse Bedload

River Channels, Earth Surface Processes and

Landforms, Vol. 8, Issue 5, pp. 503-511.

[6] Mukhopadhyay, M.(eds.) (1995): Kopai

Nadir Kada Paye, Akhil Bharat Vhuvidya O

Parivesh Samiti, Santiniketan.

[7] Pal, S. & Let, S. (2011): Channel

Morphological Trend and Relationship

Assessment of Dwarka River, Eastern India,

Global Journal of Applied Environmental

Science, Vol. 1, No. 3(2011) pp.221-232.

[8] Pal, S. (2011): Changing Inundation

Character in Mayurakshi River Basin: A

Spatio Temporal Review, Practicing

Geographer, Vol. 14, No. 1, pp. 58-71.

[9] Pal, S. (2011): River Flood: Dynamics*

Delineation* Prediction Perspective on

Subtropical Region, LAP Academic

publications, Germany.

[10] Shetye, S.R. & Gouveia, A.D. (1991): On the

Role of Geometry of Cross section in

Generating Flood Dominance in Shallow

Estuaries, Esturaine, Coastal Shelf science,

Vol. 35, pp. 113-126

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Use of Asymmetry Indices and Stability Indices for ......well as dynamism of channel configuration...

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