Drainage Morphometry Evaluation for Kodavanar sub basin to ... · 1.1 Aim and Objectives ... study...

INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES

Volume 3, No 4, 2013

© Copyright 2010 All rights reserved Integrated Publishing services

Research article ISSN 0976 – 4380

Submitted on April 2013 published on June 2013 692

Drainage Morphometry Evaluation for Kodavanar sub basin to

Understand the Interrelationships in Morphological Systems and in

Process-Response Systems

Muthukrishnan1, Manoj Kumar Sarcar

2 and Banukumar. K

3

1-Professor & Head, Department of Civil Engineering, Ponnaiyah Ramajayam College of

Engineering Technology, Anna University,Vallam, Thanjavur

2-PCCF, Department of Forests, Coimbatore Division, Mettupalayam, Tamil Nadu

3-Assistant Professor & Head, Department of Geography, Govt.Arts College Coimbatore,

Tamil Nadu

[email protected]

ABSTRACT

The utility of the drainage geomorphometric characteristics for the investigations relating to

geomorphology and hydrology has been amply demonstrated by a number of studies to

conducted various geospatial technology. The present study area is Dindigul district and its

suburbs have been frequented by heavy rains during the monsoon seasons. The river

Kodavanar which is frequently in spate during the monsoon seasons and flows through the

western part of the Dindigul and its suburbs has a large catchment area, extending to the

neighbouring Karur and Madurai Districts on the north east. The aim is to assess the

morphometric characteristics of the Kodavanar sub basin of Amaravathy basin of Tamil

Nadu. The objectives is to accomplish the aim are: to analyse the linear, areal and relief

aspects and to bring out the form and processes of the study area. In order to understand the

drainage characteristics in various parts of the Kodavanar sub basin, the basin has been

divided into 5 watersheds namely, Kodavanar-Umiyar, Anaiviludan Odai, Pudukulam

kombaiar, Todikombu and Periyakombai watersheds. Strahler‟s method of stream ordering

which is the most commonly used method of stream ordering has been followed for the

present study. For all the 5 watersheds separately, the linear, and areal and relief aspects have

been discussed. The linear aspects considered for the study include stream order, stream

number, stream length, bifurcation ratio and length ratio. The areal aspects include basin area,

form factor, circulatory ratio, elongation ratio, drainage density, stream frequency, length of

overland flow and the relief aspects considered for the present study are basin relief and

ruggedness number.

Keywords: Morphometric, Linear aspects, Areal aspects, Relief aspects.

1. Introduction

A drainage basin is an area of land drained by a river and its tributaries. It is an area of

drained by a river and its tributaries, bounded by different watershed. The relationship

between the component parts of the system can be analyzed in teams of stream order, etc.

Such method constitutes the basis of drainage basin Morphometry. It is the entire area

providing runoff to, and sustaining part or all of the stream flow of the main stream and its

tributaries. The function of the drainage basin and its significance is hinted in the synonyms,

which have gradually been adopted including drainage area, catchment area especially

employed in river control engineering, and watershed, utilized especially in water supply

engineering. Appreciation of the significance of the drainage basin unit arose with the gradual

Drainage Morphometry Evaluation for Kodavanar sub basin to Understand the Interrelationships in

Morphological Systems and in Process-Response Systems

International Journal of Geomatics and Geosciences

Volume 3 Issue 4, 2013 693

understanding of the mechanism of the hydrological cycle and of the function of the basin in

conveying water from precipitation to the river. The need to study the form of the drainage

basin derives from two main sources; firstly, to describe the form-form relationships or

morphological systems, and, secondly, to analyze the form-process relationships.

To understand the interrelationships in morphological systems and in process-response

systems it is necessary to express the character of the drainage basin in quantitative terms.

Numerous methods of describing drainage basins have been proposed; some of these apply to

the whole basin, while others apply to a particular characteristic, such as relief or soil.

Watershed planning and study of river basins have been analyses by many research works.

Being such a significant area, the present investigation has chosen to study the Morphometric

characteristic of Kodavanar Sub basin Tamil Nadu.

1.1 Aim and Objectives

The present study of investigation has set the following as its aim and fulfils the objectives:

To extract and delineate drainage morphometric characteristics (Linear, Aerial and

Relief) carried out from the topographical sheets.Delineate drainage morphometric

characteristics (Linear, Aerial and Relief) carried out from the SOI sheets, Analyse

the linear, areal and relief aspects of the study area, Bring out the form and processes,

and Finally assess the morphometric characteristics of the Kodavanar Sub-basin of

Amaravathy river basin of Tamil Nadu.

2. Study area

Kodavanar sub basin, the study area (Fig. 1) is geographically located between the North

latitudes 10o 13‟ 37” – 10

o 28‟ 30” and East longitudes 77

o 37‟ 46 – 78

o 1‟ 10”covering an

area of 716.14 sq.km. The basin possesses an elliptical shape trending in an almost NE SW

direction and forms part of the Amaravathy River Basin. Most part of the basin lies in the

Dindigul, Konur, Attur, Ulagampatti Panjapatti and Kallipatti of Dindigul District. However

the upper catchment of the basin especially northern part is covered by the Palani taluk; the

south eastern part lies in the Nilakottai taluk of Dindigul District whereas the western part

covers Kodaikanal taluk Dindigul district respectively.

Figure 1: Study Area Kodavanar Sub Basin





2.1 Geology

The study area is composed entirely of rocks belonging to the Archaean age. There are three

groups of rock structure found. Hornblende biotite gneiss and charnockite were most

dominates in the present study area. Pyroxene is found linearly to be unique in North in the

study area but their areal extent is very less. (Fig. 2).

Figure 2: Geology

3. Methodology

For the present study the Survey of India‟s topographic sheets (58 F/11, 15, &16 and 58 I/3 &

10) of 1: 50,000 scale were made use of. Basin divide was traced in order to demarcate the

study area which was followed by the digitized using Arc GIS 9.1 of drainage network falling

within the water divide. Further the basin was divided into five watershed based again on the

water divide. Strahler‟s method of stream ordering which is the most commonly used method

of stream ordering has been followed for the present study. As per the Strahler‟s method,

fingertip tributaries (all the initial, unbranched source tributaries) are of first order.

Successively higher orders are formed by the junction of two stream segments of the same

order, i.e., two first orders & second order, two second orders & third order, etc., order is not

changed when stream segments of two different orders join. Rather, the stream below such a

junction retains the higher order. Thus ordering of the streams was carried out for the two

basins. This was followed by the estimation of number of streams in each order of the basins.

By using Arc GIS Linear referencing tool, the lengths of the streams for each order were

calculate with polyconic projected coordinate system. Further, by using the tool, basin

perimeter, and basin length were found out. The areal extents of the basins were obtained by

using the 1 cm grid sheets. Details regarding the elevations in the basins were noted down

from the topographic sheets. The data thus obtained formed the basis for the study of

drainage morphometric characteristics, which includes the study of the linear, areal and relief

aspects. The procedure adopted to find out the various parameters of linear, areal and relief

aspects are given in the respective sections.

3.1 Analysis of Geomorphometry

Knowledge of morphometric characteristics of a drainage basin is an important pre-requisite

to evaluate the basin hydrology. The amount of water reaching a stream system is dependent





upon the morphometry of the basin, total precipitation, losses due to evapotranspiration and

absorbtion by solid and vegetation. The drainage basin morphometry throws light on the

lithologic and structural controls of the sub-basin; relative runoff and recharge, erosional

aspects and stage of development of basin itself. In the following sections the drainage

morphometric characteristics of the Kodavanar sub basin have been evaluated. The

procedures used for the study and the results are discussed in detail in the following sections.

3.2 Drainage Morphometric Characteristics

In order to understand the drainage characteristics in various parts of the Kodavanar sub basin,

the basin has been divided into 5 sub-basins (Fig. 3). For all the 5 sub basins, the linear, and

areal and relief aspects have been discussed in detail in the following sections.

Figure 3: Drainage

Table 1: Linear Aspects: Kodavanar Sub Basin

Sl.

No

Watershed

(WS)

Stream

Order (U)

Number

of

Streams

(Nu)

Bifurcation

Ratio

(Nu/Nu+1)

Stream

Length

in

km(Lu)

Length

Ratio

(Rl=Lu/Lu-

1)

Mean

Length in

km

(L=Lu/Nu)

1 Kodavanar

Umiyar 1,2,3,4,5,6 781 0.29 505.02 2.29 0.65

2 Anaiviludan

Odai 1,2,3,4,5,6 232 3.09 44.48 0.77 0.19

3 Pudukulam

kombai ar 1,2,3,4,5 243 3.72 226.2 0.46 0.93

4 Todikombu 1,2,3,4,6 111 4.40 179.90 2.82 1.61

5 Periyakombai 1,2,3,4,5,6,7 462 3.14 433.84 1.00 0.94

Whole 1,2,3,4,5,6,7 1829 2.93 1389.44 1 0.76





3.3 Linear Aspects: Kodavanar Sub Basin

Linear aspects of the basins are related to the channel patterns of the drainage network

wherein the topological characteristics of the stream segments in terms of open links of the

network system (streams) are analysed. The drainage network, which consists of all of the

segments of streams of a particular river, is reduced to the level of graphs, where stream

junctions act as points (nodes) and streams which connect the points (junctions), become

links or lines wherein the number of all segment are counted, their hierarchical orders are

determined, the length of all stream segments are measured and their different

interrelationships are studied. Thus, the study of linear aspect includes the analysis of stream

order, stream number, bifurcation ratio, stream lengths and length ratio. Stream ordering

refers to the determination of the hierarchical position of a stream within a drainage basin. A

river basin consist of several branches (segments) having different positions in the basin area

and they have their own morphometric characteristics and, therefore, it becomes necessary to

locate the relative position of a segment in the basin, so that the hierarchical organization of

stream segments is visualized. Thus, stream order is a measure of the position of a stream in

the hierarchy of tributaries. Though there are number of methods for stream ordering such as

Gravelius method, Horton‟s method, Strahler‟s method, Shreeve‟s method, Scheidegger‟s

method, etc, the most commonly and widely followed method is that of the Strahler‟s.

According to Strahler, each fingertip channel is designated as a segment of first order. At the

junction of any two first order segments, a channel of 2nd

order is produced and extends

down to the point, where it joins another second order segment whereupon a segment of third

order results and so forth. These streams may have additional stream segments of lower

orders than their own order and thus these do not affect the classification. It may be

mentioned that the hierarchical order increases only when two stream segments of equal

order meet and form a junction. The order does not increase if a lower order stream segment

meets a stream segment of higher order. For the present study Strahlers method stream

ordering which is described above has been made use of for ordering the stream segments.

The stream ordering carried out for the Kodavanar sub basin has shown that the Kodavanar

River is a seventh order stream. The stream orders for the 5 sub basins are presented in table

1. Form the table it is evident that among the watershed, highest stream order (7th

order) is

found for Periyakombai. In all other sub basins the maximum stream order is found to be of

6th

order. After ordering the streams, the number of stream segments of each order was

counted for each sub basin and for the whole Kodavanar sub basin. The results are presented

in table no.1 to 8. From the tables it is evident that in the entire Kodavanar sub basin there

are 1829 stream numbers. Among the watersheds, the stream numbers are found to vary from

111 (Todikombu watershed) to 781 (Kodavanar-Umiyar watershed). Stream numbers are

observed to be high (> 400 stream numbers) in Kodavanar and Periaykombai watersheds;

moderate (200-300) in Pudukulam kombai ar and Anaiviludan Odai watersheds; and low (<

150) in Todikombu watershed. The percentage of stream numbers of various stream orders in

the basin are 75.71, 17.67, 4.76, 1.15, 0.44, 0.22, and 0.05 for the first, second, third, fourth,

fifth, sixth and seventh order streams. The percentage of stream numbers of various stream

orders for each sub basin of Kodavanar sub basin is shown in Table 1. Among the various

watersheds, the percentage of streams is found to range from 42.70 per cent (for Kodavanar-

Umiyar watershed), 25.25 per cent (Periyakombai watershed), 13.29 per cent (Pudukulam

kombai ar watershed), 12.68 per cent (Anaiviludan Odai watershed) and 6.07 per cent

(Todikombu watershed). Bifurcation ratio is the ratio of the number of streams of a given

order (Nu) to the number of streams of the next higher order (Nu+1) and is expressed in

terms of the following equation (Strahler, 1952). Rb = Nu / Nu+1 Where Rb = Bifurcation

ratio, Nu = Number of streams of a given order, Nu + 1 = Number of streams of a given next





higher order , The bifurcation ratio values obtained for the entire Kodavanar sub basin and its

sub basins are given in table 1. From the table it is evident that the average bifurcation ratio

value obtained for the basin is 2.93. Among the watersheds, bifurcation ratio is found to

range from 0.29 (for Kodavanar-Umiyar watershed) to 4.40 (for Todikombu). Bifurcation

ratio value was found to be high for Todikombu (4.40) and Pudukulam kombai ar (3.72)

watersheds. In all other watersheds, it is found to be ranging between 2 and 5, a range

characteristic of basins with well developed drainage network. Remains are reduced to the

network of drainage.

The length of the various stream segments of the watershed and the entire Kodavanar sub

basin was found out using ArcGIS 9.1 Linear referencing tool were used and the result are

shown in table 1. From the table it is evident that the total length of the streams for the entire

Kodavanar sub basin is 1389.44 km. Among the watershed, it is found to vary from 44.48 km

(for Anaiviludan Odai watershed) to 505.02 km. (for Kodavanar-Umiyar watershed). Among

the watersheds, stream length was found to be low (< 100 km.) for Anaiviludan Odai

watershed. It was found to be moderate (100-200 km.) for Todikombu watershed and high (>

200 km.) for Periyakombai, Kodavanar-Umiyar watershed. The proportion of increase of

mean length of stream segments of two successive basins of orders is defined as length ratio

(Savindra Singh, 2000). The length ratio computed for the entire sub basin is found to be 1

(Table 1). Among the watershed, the average length ratio value is found to range from 0.46

(for Pudukulam kombai ar watershed) to 0.77 (for Anaiviludan Odai). The average length

ratio was found to be relatively high (>2) for Todikombu and Kodavanar-Umiyar watershed;

moderate (ranging from 0.5 to 1.00) for Anaiviludan Odai, and Periakombai watersheds, and,

low (> 0.6) for Pudukulam kombai ar.

Table 2: Areal Aspects: Kodavanar Sub Basin

S

l.

N

o

Watershed

(WS)

Are

a in

Sq.

km

(Au

)

Peri

mete

r in

km

(P)

Lengt

h in

km

(Lb)

Form

Factor

(Rf=Au/

Lb2)

Circulator

y Ratio

(Rc=((4π*

Au)/P2)

Elongat

ion

Ratio

(Re=(2

√Au/π)/

Lb)

Drain

age

Densit

y

(Du=

Lu/Au

)

Stream

Freque

ncy

(Fs=Nu

/Au)

Length

of over

land

flow

(Lg=1/

2*Du)

1 Kodavanar

Umiyar

166

.86

80.4

5 27.83 0.22 0.32 0.38 0.17 4.68 0.083

2 Anaiviludan

Odai

108

.74

50.9

9 13.8 0.57 0.53 0.72 0.13 2.13 0.063

3 Pudukulam

kombai ar

126

.04

70.3

2 23.36 0.23 0.32 0.42 0.19 1.93 0.093

4 Todikombu 121

.4

61.1

7 23.75 0.22 0.41 0.40 0.20 0.91 0.098

5 Periyakomb

ai

193

.08

76.6

6 28.08 0.24 0.41 0.43 0.15 2.39 0.073

Whole

716

.12

137.

12 43.01 0.39 0.48 0.22 0.06 2.55 0.030

3.4 Areal Aspects of Kodavanar Sub Basin

The areal aspects considered of the drainage basin include the study of sub basin area sub

basin perimeter, basin shape (form factor, circularity ratio and elongation ratio), drainage





density, stream frequency and length of overland flow. The procedures adopted to study the

above parameters are given in the following section and the estimates made are given table 2.

Basin area is an important morphometric attribute as it is related to the spatial distribution of

a number of significant attribute such as drainage density, stream frequency, relative relief

etc., For the present analysis the basin area was measured with the help of ArcGIS 9.1 linear

referencing tool. The area thus computed for the Kodavanar sub basin and its watersheds

basins are shown in table 2. Estimates reveal that the areal extent of the Kodavanar sub basin

is 716.12 sq. km. and there exists substantial variation in the areal extent of the sub-basins,

ranging from 108.74 sq.km (for Anaiviludan Odai watershed) to 193.08 (Periyakombai

watershed). The areal extent was found to be relatively high (> 150 sq. km.) for Periakombai

and Kodavanar-Umiyar watersheds; low (100-150 sq. km.) for Anaiviludan Odai, Todikombu

and Pudukulam watersheds.Basin length is defined as the longest length in the basin, one end

being the mouth Gregory and Walling (1973). Based on the above definition, the length of

the Kodavanar sub basin and its watersheds were estimated and are given in table 2. The

length of the Kodavanar sub basin is found to be 43.01 km. Among the watersheds, the basin

length is found to range from 13.08 km. (Anaiviludan Odai) to 28.08 km. (Periyakombai

watershed). Watersheds with relatively low (< 15 km.) basin length are Anaiviludan Odai

watershed; moderate (15 to 25 km.) in Pudukulam kombai ar and Todikombu watersheds and

those with high (> 20 km.) basin length are Kodavanar-Umiyar and Periyakombai watersheds.

The geometry of basin shape is paramount significance as it helps in the description and

compurgation of different forms of the drainage basin and it is also related to the functioning

of the units of the basin and its genesis. The ideal drainage basin is usually of pear shape but

since is dependent on the size and the length of the master stream of the basin perimeter,

which are they dependent on other variables such as absolute relief's, slopes, geological

structure and litho logical characteristics.Thus various methods have been suggested to

calculate the shapes of the basin. They are all 3 categories.1. Form factor (F)2. Circularity

Ratio (Cr)3. Elongation Ratio (Er) Basin shape is the direct outcome of the drainage

development in a particular basin. It is evidenced that the basins are pear shaped in early

stages and as the erosion cycle advances, the shape becomes more elongated (Padmaja rao,

1978). Though there a number of measures for determining the basin shape, for the present

study, form factor suggested by Horton. According to Horton (1932), Form Factor (Rf) =

Au/Lb2

Where Rf= Form Factor, Au = Area of the basin, Lb = Maximum longest length of

the basin, The value of „F‟ varies from 0 (highly elongated shape) to 1 (perfect circular

shape). Thus, higher the value of F, more circular the shape of the basin and vice-versa. For

the present study form factor values were obtained for the Kodavanar sub basin and its

watersheds and are shown in table 2. For the Kodavanar sub basin , the form factor value

was found to be 0.22, which reflects its highly elongated shape. Among the watersheds form

factor values are found to range from 0.22 (for Kodavanar-Umiyar, Todikombu watersheds)

to 0.57 (for Anaiviludan Odai watershed) which clearly indicate the elongate nature of the

sub basins. In view of the relative high form factor values for the Anaiviludan Odai and

Kodavanar-Umiyar watershed, it could be reasonable to assume that these two sub basins are

less elongated than the rest of the other sub basins of the study area. The result of circularity

ratio ranges between 0.32 and 0.53 for the all five watersheds. Todikombu and Periakombai

watershed 0.41, and 0.41 is lower than rest of other watersheds. Anaiviludan Odai watershed

highest circularity ratio is 0.53 is reflects this watershed is closely to circle shape. The

computed Elongation Ratio is ranges between 0.38 and 0.72 in the Kodavanar sub basin for

the all five watersheds. The lower value of elongation ratio is found 0.38 in the Kodavanar-

Umiyar watershed. The highest values of elongation ratio Anaviludan Odai is to be found. It

is indicate this watershed is closely to the circle. drainage density values for the Kodavanar

sub basin and its watersheds have been computed and are shown in table 2. From the table, it





is evident that the drainage density for the basin is 0.06 km / sq. km. Among the watersheds,

drainage density values are found to range from a maximum of 0.20 km / sq. km (Todikombu

watershed) to a minimum of 0.13 km / sq. km (Anaiviludan Odai watershed). The

watersheds where the drainage density is relatively high (> 0.20 km / sq. km) are Todikombu.

Drainage density is found to be relatively low (< 0.15 km / sq. km) in the Periakombai

watershed. In rest of the basins, the drainage density is found to be low. The stream

frequency values obtained for the Kodavanar and its watersheds are given in table 2. The

stream frequency value obtained for the basin is 2.55. Among the watersheds, it ranges from

4.05 (Mamundiyar sub basin) to 0.70 (Kilayur sub basin).

The sub basins where the stream frequencies are relatively higher (> 4) are Kodavanar-

Umiyar Watershed. In the Anaiviludan Odai it is moderate (2-4) and is low (< 2) in the

Pudukulam kombai ar and Todikombi watersheds. The length of overland flow is a measure

of stream spacing or degree of dissection. Horton (1945) used this term to refer to the length

of the runoff the rainwater on the ground surface before it gets localized into definite

channels. Since this length of overland flow at an average is about half the distance between

the streams channels. Horton for the sake of convenience had taken it to be roughly equal to

half the reciprocal of drainage density. For the present analysis half the reciprocal of

drainage density values for the Kodavanar sub basin and its watersheds were estimated and

are shown in table 2. From the table, it is evident that the length of overland flow value for

the Kodavanar sub basin is 0.03 It means, the rainwater on an average has to run over 0.03

km before getting concentrated in stream channels. The length of overland flow ranges from

0.063 km (Anaiviludan Odai watershed) to 0.098 (Todikombu). The overland flow value is

found to be relatively high (> 0.09 km) in Todikombu watershed. This reflects that rain water

has to travel relatively slight distances before getting concentrated into stream channels. On

the other hand, the length of overland flow is relatively low (< 0.063 km) in Anaiviludan

Odai watershed. This indicates that the rainwater will enter the stream very quickly in these

basins. In rest of the sub basins it is found to be quickly in these basins.

Table 3: Relief Aspects: Kodavanar Sub Basin

Sl.

No

Watershed

(WS)

Wate

rshe

d

Mou

th

Heig

ht in

mts

(z)

Wat

ersh

ed

High

est

Poin

t in

mts

(Z)

Watersh

ed

Relief

(H=Z-z)

Watersh

ed

Length

(Lb)

Relief

Ratio

(Rh=H/

Lb)

Drainage

Density

(Du=Lu/

Au)

Ruggedness

Number

(Rn=Du*H/5

280)

1 Kodavanar

Umiyar 277 1980 1703 27.83 61.19 0.17 0.05

2 Anaiviludan

Odai 240 1167 927 13.8 67.17 0.13 0.02

3 Pudukulam

kombai ar 235 1406 1171 23.36 50.13 0.19 0.04

4 Todikombu 225 1256 1031 23.75 43.41 0.20 0.04

5 Periyakombai 365 1437 1072 28.08 38.18 0.15 0.03

Whole 225 1980 1755 43.01 40.80 0.06 0.02





3.5 Relief Aspects of Kodavanar Sub Basin

The relief aspects of the drainage basins are related to the study of the three dimensional

features of basins involving area volume and attitude of vertical dimension of landforms. The

relief aspects considered for the present study are basin relief and ruggedness number. Basin

relief was computed by finding the arithmetic difference between the maximum and the

minimum elevations in a given basin. The basin relief values thus computed for the sub

basins of the study area are shown in table 3. For the Kodavanar sub basin, the basin relief is

found to be 1755 mts Msl. Among the watersheds, basin relief varies from 927 m

(Anaiviludan Odai) to 1703 m (Kodavanar-Umiyar watershed). Basin relief was found to be

very high (> 1500 m.) in Kodavanar-Umiyar watershed; high (1000-1500 m.) in Pudukulam

kombai ar, Todikombu and Periyakombai watersheds; moderate (<1000 m.) in Anaviludan

Odai watershed. The ruggedness number values calculated by using the above relationship

are given in table 3. The ruggedness number value for the whole Kodavanar sub basin is

found to be 0.02. Among the watersheds, it ranges from 0.02 (Anaiviludan Odai watershed)

to 0.05 (Kodavanar-Umiyar watershed). Ruggedness number was observed to be high (> 0.5)

for Kodavanar-Umiyar watershed; moderate (0.02-0.03) for Anaiviludan Odai, Periyakombai

watershed.

4. Inference from of the Kodavanar Basin and its watersheds using Drainage

Morphometric Characteristics

The previous chapters dealt with works relating to the drainage Morphometric characteristics

conducted in various parts of the world have proved that the measurements of the linear, areal

and relief aspects can serve as parameters to understand the drainage network and

measurements within a drainage basin. In the present chapter dealing with the inferences

drawn from the analysis of the Morphometric characteristics of the Kodavanar sub basin has

been synthesized.

4.1 Analysis of Linear aspects

4.1.1 Analysis of Stream Order

Gregory and Walling (1973) have found that the increasing order of network is associated

with greater stream flow values. According to the authors, is evident that Kodavanar-Umiyar,

Periyakombai watersheds are to have greater stream flow than the rest of the other sub basins

of the study area. Horton evolved a model of stream order (U) and stream number (Nu) that

the number of channels of each order is inverse geometric series with stream number. This

has been widely tested in different parts of the world.

The data of stream order and stream number of Kodavanar sub basin exhibit the orderly

arrangement of the number of streams of different orders. It is evident form the plots on a

graph 1 that the number of stream decrease with an increase in order, there by the correlation

function is negative. The points generally fall close to a straight line. The common negative

correlation of basin is expressed by the following equation;

Y= 17.471x; R2 = - 0.2803

When the average of stream numbers in all the lithological groups is taken, the higher number





of streams fall in the category of the Kodavanar-Umiyar watersheds.

4.1.2 Analysis of Bifurcation ratio

According to Savindra Singh et al. (1984), the mean bifurcation ratios of the basins of

mountainous and dissected regions are slightly more than the basins of flat and rolling

surfaces. In the study area, Kodavanar, Periyakombai and Anaiviludan Odai watersheds have

substantially high bifurcation ratios and hence it could be inferred that these sub basins flow

through mountainous and dissected regions. On the other hand, Todikombu and Pudukulam

kombai ar watersheds on account of their high ratio values are likely to flow through flat and

rolling topography. Horton (1945) and Strahler (1957) have found that the bifurcation ratio

ranges from 2 to 5 in basins with well developed drainage network.

As the bifurcation ratio value estimated for the basin (4.40) is within this range, it can be

concluded that the Kodavanar sub basin possesses well developed drainage network.Horton

suggested that the slope of the fitted lines represent the mean bifurcation ratio of the series.

According to Horton considered the bifurcation ratio as an index of relief and dissection.

Number of pioneers pointed out that the bifurcation ratio on mature surfaces tend to have

values 3 to 5, with an usual value around 4 bifurcation ratio is the ratio of the total number of

streams of one order to that of the next higher order.

Because of chance irregularities, bifurcation ration between successive pairs of orders differs,

within the same basin even if a general observance of a geometric series exists (Schumm,

1956). To arrive at amore representative bifurcation number, Strahler (1953) used weighted

mean bifurcation ratio. The calculated bifurcation ratio is plotted in graph 2. This graph is

represented that the bifurcation ration shows a smaller range of variation is found along the

Kodavanar- Umiyar watershed and Anaiviludan Odai where powerful geological (Ac-

Charnockite group. character-predominates.

4.1.3 Analysis of Stream Length

Morisawa (1962) has observed that the total stream length is directly related to the mean

annual run off. Based on this observation, it is very likely that Periyakombai Ar, and

Kodavanar-Umiyar watersheds would have greater annual run off. Remaining watersheds are

Pudukulam kombai ar, Anaiviludan Odai and Tadikombu on account of their moderate

stream lengths are likely to have moderate annual run off.

4.1.4 Analysis of Length ratio Data

According to Kumarawamy and Sivagnanam (1988), larger the length ratio values, more the

lower order sources for the next higher order streams, whereas, smaller values indicate the

limited length of lower order streams to serve as hydrological sources. Based on this

observation, it is inferred that for Anaiviludan Odai and Periyakulam kombai ar watersheds,

there are lower order sources for the next higher order streams. On the otherhand for

Kodavanar-Umiyar, Todikombu and Periyakombai watersheds, the lower length ratio values

indicate the limited length of lower order streams to serve as hydrological sources.





Figure 4: Watershed

4.2 Analysis of Areal aspects

4.2.1 Analysis of Basin Area

Morisawa (1962) have found that the mean annual run off is directly related to drainage basin

area. This suggests that among the watersheds of the study area, the mean annual run off is

higher for the Periyakombai and Kodavanar-Umiyar Kilayur watersheds whereas it is low for

Anaiviludan Odai watershed.

4.2.2 .Analysis of Form Factor

According to Horton (1932), the form factor value varies from 0 (highly elongated shape) to

the unity i.e., 1 (perfect circular shape). Thus, the higher the value of form factor, the more

the circular the shape of the basin and vice-versa. The form factor value (0.39) estimated for

the Kodavanar sub basin reveals that the basin is elongated in shape. Among the watersheds,

the form factor values ranges from 0.22 to 0.57 which clearly shows that all the sub basins

are elongated in nature. However, on account of slightly higher form factor values for the

Anaiviludan Odai watersheds, these are likely to be less elongated.

4.2.3 Analysis of Drainage Density

According to Carlston (1963), drainage density is inversely related to permeability of the

terrain. The higher the drainage density the lesser the permeability of the terrain. From this

observation it could be inferred that the terrain in watersheds with higher drainage density

such as Todikombu and Periyakulam kombai ar is likely to be less permeable. Whereas, the

terrain in sub basins with lower drainage density such as Kodavanar-Umiyar, Anaiviludan

Odai, and Periyakombar is relatively more permeable.





4.2.4 Analysis of Stream Frequency

Stream frequency reflects the degree of dissection of the terrain. The higher the stream

frequency, the greater the degree of dissection. On account of the relatively high stream

frequency, the watersheds Kodavanar-Umiyar, Anaiviludan Odai and Periyakombai are likely

to be more dissected. However, Pudukulam kombai ar, and Todikombu watersheds on

account of their low stream frequency values are likely to be less dissected.

4.2.5 Analysis of Length of Overland Flow

Length of overland flow is one of the most important Morphometric variables, which affects

the hydrological and topographic development of the basins. According to Coates (1958)

other factors being constant, areas more advanced into maturity appear to contain smaller

overland flow lengths that youthful areas because a drainage basin on an average develops

maximum stream segments in its late youth and early mature stages and thus minimum

(shorter) length of overland flow is found (Savindra Singh, 2007).

From these observations it is inferred that within the sub basin, the watersheds such as

Anaiviludan Odai and Periyakombai watersheds on account of their low values are more

matured.

Basins with lower overland flow values also indicate that in such basins less rainfall is

sufficient to contribute a significant volume of surface run off to stream discharge. In the

study area in the Anaiviludan Odai and Periyakombai watersheds, less rainfall is sufficient to

contribute a significant volume of surface run off to stream discharge. On the other hand in

Todikombu watershed which possesses higher length of overland flow, the case is reverse.

For the Kodavanar sub basin the length of overland flow value is found to be 0.063 i.e., the

rainwater on an average has to run over 0.063 km. before getting concentrated in stream

channels. In Todikombu watershed where the length of overland flow value is higher, the rain

water has to travel relatively longer distance before getting concentrated into stream

channels. In watersheds such as Kodavanar-Umiyar, Anaiviludan Odai, Pudukulam kombai

ar and Periyakombai (where the value is low), rainwater will enter the stream quickly.

4.3 Analysis of Relief aspects

4.3.1 Analysis of Ruggedness Number

According to Patton (1988), the relative peak discharge ratio increases with the increase in

ruggedness number. From this observation, it is inferred that in the sub basins such as

Kodavanar-Umiyar, Pudukulam kombai ar and Todikombu watersheds (where the

ruggedness number value is higher), the peak discharge rates are likely to be higher. On the

other hand the discharge rates are likely to be less in the Anaiviludan Odai and Periyakombai

watersheds in view of their lower ruggedness number values.

5. Conclusion

The present study analyse the morphometric three aspects for their origin and destination of

river system. But the Kodavanar River confluence with the Amaravathy river, it is a major

tributaries of River Cauvery. Following sections are described their response of the rivers





process and inferences of running water. The linear aspects contains stream order (U),

Number of Streams (Nu), Bifurcation ratio (Bf), Stream length, and Length ratio.

The stream ordering carried out for the Kodavanar basin has shown that the Kodavanar River

is a seventh order stream. Among the watersheds, highest stream order (7th

order) is found for

Kodavanar-Umiyar, Todikombu watersheds. In all other watersheds the maximum stream

order is found to be of 6th

order in the entire Kodavanr sub basin there are 1829 stream

numbers. Among the watersheds, the stream numbers are found to vary from 110

(Todikombu watershed) to 781 (Kodavanar-Umiyar watershed). Stream numbers are

observed to be high (> 400 stream numbers) in Kodavanar and Periaykombai watersheds;

moderate (200-300) in Pudukulam kombai ar and Anaiviludan Odai watersheds; and low (<

150) in Todikombu watershed. The percentage of stream numbers of various stream orders in

the basin are 75.71, 17.67, 4.76, 1.15, 0.44, 0.22, and 0.05 for the first, second, third, fourth,

fifth, sixth and seventh order streams. The percentage of stream numbers of various stream

orders for each sub basin of Kodavanar sub basin is shown in Table 1. Among the various

watersheds, the percentage of streams is found to range from 42.70 per cent (for Kodavanar-

Umiyar watershed), 25.25 per cent (Periyakombai watershed), 13.29 per cent (Pudukulam

kombai ar watershed), 12.68 per cent (Anaiviludan Odai watershed) and 6.07 per cent

(Todikombu watershed).The bifurcation ratio values obtained for the entire Kodavanar sub

basin and its sub basins are given in table 1. From the table it is evident that the average

bifurcation ratio value obtained for the basin is 2.93. Among the watersheds, bifurcation ratio

is found to range from 0.29 (for Kodavanar-Umiyar watershed) to 4.40 (for Todikombu).

Bifurcation ratio value was found to be high for Todikombu (4.40) and Pudukulam kombai ar

(3.72) watersheds. In all other watersheds, it is found to be ranging between 2 and 5, a range

characteristic of basins with well developed drainage network. Remains are reduced to the

network of drainage.The length of the streams for the entire Kodavanar sub basin is 1389.44

km. Among the watershed, it is found to vary from 44.48 km (for Anaiviludan Odai

watershed) to 505.02 km. (for Kodavanar-Umiyar watershed). Among the watersheds, stream

length was found to be low (< 100 km.) for Anaiviludan Odai watershed. It was found to be

moderate (100-200 km.) for Todikombu watershed and high (> 200 km.) for Periyakombai,

Kodavanar-Umiyar watershed.The length ratio computed for the entire basin is found to be 1.

Among the watershed, the average length ratio value is found to range from 0.46 (for

Pudukulam kombai ar watershed) to 0.77 (for Anaiviludan Odai). The average length ratio

was found to be relatively high (>2) for Todikombu and Kodavanar-Umiyar watershed;

moderate (ranging from 0.5 to 1.00) for Anaiviludan Odai, and Periakombai watersheds, and,

low (> 0.6) for Pudukulam kombai ar. The areal aspects considered of the drainage basin

include the study of sub basin area sub basin perimeter, basin shape (form factor, circularity

ratio and elongation ratio), drainage density, stream frequency and length of overland flow.

Estimates reveal that the areal extent of the Kodavanar sub basin is 716.12 sq. km. and there

exists substantial variation in the areal extent of the sub-basins, ranging from 108.74 sq.km

(for Anaiviludan Odai watershed) to 193.08 (Periyakombai watershed). The areal extent was

found to be relatively high (> 150 sq. km.) for Periakombai and Kodavanar-Umiyar

watersheds; low (100-150 sq. km.) for Anaiviludan Odai, Todikombu and Pudukulam

watersheds. The Kodavanar sub basin and its watersheds have been computed and are shown

in table 2. From the table, it is evident that the drainage density for the basin is 0.06 km / sq.

km. Among the watersheds, drainage density values are found to range from a maximum of

0.20 km / sq. km (Todikombu watershed) to a minimum of 0.13 km / sq. km (Anaiviludan

Odai watershed). The watersheds where the drainage density is relatively high (> 0.20 km /

sq. km) are Todikombu. Drainage density is found to be relatively low (< 0.15 km / sq. km)

in the Periakombai watershed. In rest of the basins, the drainage density is found to be





low.The Kodavanar and its watersheds are given in table 2. The stream frequency value

obtained for the basin is 2.55. Among the watersheds, it ranges from 4.05 (Mamundiyar sub

basin) to 0.70 (Kilayur sub basin). The sub basins where the stream frequencies are relatively

higher (> 4) are Kodavanar-Umiyar Watershed. In the Anaiviludan Odai it is moderate (2-4)

and is low (< 2) in the Pudukulam kombai ar and Todikombi watersheds. The relief aspects

of the drainage basins are related to the study of the three dimensional features of basins

involving area volume and attitude of vertical dimension of landforms.Basin relief was

computed by finding the arithmetic difference between the maximum and the minimum

elevations in a given basin. The basin relief values thus computed for the sub basins of the

study area are shown in table 3. For the Kodavanar sub basin, the basin relief is found to be

1755 mts Msl. Among the watersheds, basin relief varies from 927 m (Anaiviludan Odai) to

1703 m (Kodavanar-Umiyar watershed). Basin relief was found to be very high (> 1500 m.)

in Kodavanar-Umiyar watershed; high (1000-1500 m.) in Pudukulam kombai ar, Todikombu

and Periyakombai watersheds; moderate (<1000 m.) in Anaviludan Odai watershed. The

ruggedness number values calculated by using the above relationship are given in table 3.

The ruggedness number value for the whole Kodavanar sub basin is found to be 0.02. Among

the watersheds, it ranges from 0.02 (Anaiviludan Odai watershed) to 0.05 (Kodavanar-

Umiyar watershed). Ruggedness number was observed to be high (> 0.5) for Kodavanar-

Umiyar watershed; moderate (0.02-0.03) for Anaiviludan Odai, Periyakombai

watershed.From the analysis of the various types drainage morphometric characteristics of

the Kodavanar sub basin and its watersheds the following inferences have been made: The

analysis of stream order data shows that Kodavanar-Umiyar, Anaiviludan odai watersheds are

likely to have greater stream flow than the rest of the other watersheds of the study area. The

analysis bifurcation value shows that basin and its watersheds possesses well developed

drainage network. Further the values show that the Kodavanar-Umiyar, Periyakombai Ar and

Anaiviludan Odai watersheds flow through mountainous and dissected regions. On the

otherhand, Tadikombu, and Pudukulam kombai ar on account of their low ratio values are

likely to flow through flat and rolling topography. The analysis of stream length data shows

that Kodavanar-Umiyar, Periyakombai ar watersheds would have greater annual run off;

whereas, Todikombu, and Pudukulam kombai ar on account of their lower stream lengths are

likely to have lower annual run off.The analysis of basin area data reveals that the mean

annual run off is higher for the Kodavanar-Umiyar, Periyakombai ar watersheds whereas it is

low for Tadikombu, Pudukulam kombai ar watersheds. The analysis of form factor values

reveals that the basin and its sub basins are highly elongated in shape. However, on account

of lower form factor values for the Kodavanar-Umiyar, Periyakombai ar , Tadikombu,

Pudukulam kombai ar and Periyakombai ar watersheds Sangalar, these are likely to be high

elongated from the circle shape. But the Anaiviludan Odai watershed is less elongated from

their shape. From the analysis of drainage density data, it is inferred that the watersheds with

lower drainage density such as Anaiviludan Odai, Periyakombai ar, are likely to possess

relatively more permeable sub surface materials, whereas the sub surface material in the

Kodavanar-Umiyar, Pudukulam kombai ar watersheds is likely to be less permeable. The

result of circularity ratio ranges between 0.32 and 0.53 for the all five watersheds.

Todikombu and Periakombai watershed 0.41 and 0.41 is lower than rest of other watersheds.

Anaiviludan Odai watershed highest circularity ratio is 0.53 is reflects this watershed is

closely to circle shape.The computed Elongation Ratio is ranges between 0.38 and 0.72 in the

Kodavanar sub basin for the all five watersheds. The lower value of elongation ratio is found

0.38 in the Kodavanar-Umiyar watershed. The highest values of elongation ratio Anaviludan

Odai is to be found. Its indicate this watershed is closely to the circle. The analysis of stream

frequency values indicate that the watersheds Kodavanar-Umiyar, Periyakombai ar and

Anaiviludan odai watersheds are likely to be more dissected; whereas, Pudukulam kombai ar





and Tadikombu watersheds on account of their low stream frequency values are likely to be

less dissected. The analysis of length of overland flow data reveals that that within the basin,

the sub basins such as Kodavanar-Umiyar, Anaiviludan Odai on account of their low values

are more matured. Further in these sub basins, less rainfall is sufficient to contribute a

significant volume of surface run off to stream discharge. On the other hand in Pudukulam

kombai ar, Todikombu, Periyakombai ar which possesses higher length of overland flow, the

case is reverse. Further, the length of overland flow value for the Kodavanar sub basin is

found to be 0.030 which implies that the rainwater on an average has to run over 0.030 km.

before getting concentrated in stream channels. In Todikombu watershed where the length of

overland flow value is little higher, the rain water has to travel relatively longer distance

before getting concentrated into stream channels. In sub basins such as Kodavanar-Umiyar

and Anaiviludan Odai (where the value is low), rainwater will enter the stream quickly. The

analysis of ruggedness number value suggests that in watersheds such as Kodavanar-Umiyar,

Pudukulam kombai ar, and Todikombu watersheds (where the ruggedness number value is

slight higher), the peak discharge rates are likely to be higher. On the other hand the

discharge rates are likely to be less in the Periakombai and Anaiviludan Odai watersheds in

view of their lower ruggedness number values.Final word, the present study thoroughly

analysed the Drainage Morphometry Evaluation for Kodavanar sub basin to understand the

interrelationships in morphological systems and in process-response systems is proved to

entire terrain of the study area.

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