morphometric characteristics of linear and areal...
TRANSCRIPT
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CHAPTER IV
Morphometric Characteristics of Linear and Areal
Aspects of the Basin
The noted hydraulic engineer R. E. Horton (1945) laid the foundation of
quantitative and systematic approach in geomorphology based on morphometric
techniques. The drainage basin is generally regarded as the most satisfactory basic
unit for study because it is an areal unit and drainage systems can be placed in orderly
hierarchies. Interest in drainage basin morphometry has grown since Horton drew
serious attention in 1945 to certain basic laws. The work of Horton has been built
upon and extended since then and knowledge of the mathematical properties of
drainage basins had been greatly extended. Thus, in any geomorphological study,
drainage analysis has become an important part as described in the following pages.
4.1 Linear aspects of the Basin
Linear aspects of the drainage basin include the channels and their network in
terms of open links wherein the topological properties of the stream segments are
analysed. The drainage network which consists of all the stream segments of a
particular river helps to study in graphic terms, where in stream junctions are
considered as points while the streams are regarded as the lines. For this purpose, the
numbers of all the stream segments (Nu) are counted, their hierarchical orders are
determined, the lengths of the stream segments are measured and the various inter
relationships are analysed.
The length of overland flow (Lg) is the mean distance from the watershed to
the stream of the first order having no direct channel in a drainage planform. This
length of overland flow is very much significant in the study of drainage basins.
Because it denotes the spacing of streams. The length of the master stream (L) from
the mouth to the source is called the “mesh length”. It has a significance in the
discussion of the drainage basin concerned.
In the present study, the data of various attributes of linear aspects of the basin
have been derived and calculated base on the toposheets of R.F. 1:63,360. The
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following few articles follow the discussion on some of the aspects of the Kaldiya
river basin.
4.1.1. Stream Order
Different stream segments of a drainage basin have their definite positions in
the domain of drainage basin. They have their distinct morphometric characteristics
which necessitate the determination of their relative positions on the hierarchical scale
of stream segments. Stream order is defined as a measure of the position of a stream
in the hierarchies of tributaries.
Davis (1899) described the drainage basin as a leaf and the streams as the
veins of that leaf. It was Gravelius (1914) who made the first systematic attempt to
discuss on the hierarchical orders of the streams of a drainage basin by tracing the
streams from the mouth to the source. He tried to recognize the trunk stream through
greatest width, discharge, headward branching and junction angle which he allotted
the position of first order. He assigned the second order to those straems which join
the main streams of 1st order and so on.
System of channel ordering were suggested by Horton (1945) and Strahler
(1952) excluding Gravelius (1914). The work of Horton marked the beginning of the
concept of stream ordering. It was further modified by Strahler to overcome some of
the limitations of Horton’s ordering system (Fig. 4.1). Horton’s scheme of ordering of
streams is difficult, tedious and time consuming. Strahler (1952, 53, 57) modified to
reduce the limitations of the Horton’s (1945) ordering system. He proposed a simple
scheme out of Horton’s method. By this method, Strahler simplifies the computation
but it reduces the length of the main trunk, because the method of giving order
number is restricted to stream segments only.
In the present study, the researcher has applied the Strahler’s scheme and
method of stream ordering. According to Strahler ‘each finger- tip channel is
considered as a segment of the first order. At the junction of any two first order
segments, a channel of second 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.
Following the Strahler’s (1952) ordering system, it is found that the main
channel of the Kaldiya river system conforms to a fifth order basin. Out of 11
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80
significant sub-basins, 10 are third order sub-basins, and only 1 is fourth order basin.
All the eleven sub-basins except the Kaldiya river basin itself are the tributary basins
in the study area. The major tributary streams, viz-Buradiya river (4th
), Deojara river
(3rd
), Bhumki river (3rd
), Moradiya river (3rd
), Bhalukjuli river (3rd
) Bahbari river
(3rd
), Bogajuli river (3rd
), Daijima river (3rd
), Turkuni river (3rd
), Dirang (3rd
) and
Jorabari (3rd
), have drainage tracks ranging up to fifth order (Table 4.1 and Fig. 4.1)
The permeable nature of lithology and the low relief characteristics give a
minimum number of first and second order streams in the lower part of the basin
comprising mainly the alluvial plains. Actually the soils ranging from loamy to sandy
loamy nature have restricted dense growth and development of even the ideal number
of lower order streams in this part (Fig. 4.2)
4.1.2 Stream Number
The number of segments of each order is counted and denoted by Nu (Table
4.1). In an ideal condition the number of stream segments in a drainage net decrease
with increasing orders following a certain constant ratio called the bifurcation ratio
(Horton, 1945). Bifurcation has its significant role in the analysis of branching pattern
of drainages in the Kaldiya river basin like others.
Table 4.1 Kaldiya Basin : Orderwise Number of Stream Segments
Sl.
No.
Name of the
Sub Basin
Orderwise Number of Stream
Segments (Nu) Order Status of
the Basin First
Order
Second
Order
Third
Order
Fourth
Order
1 Deojara 9 7 3 3rd
2 Jorabari 10 6 2 3rd
3 Moradiya 16 5 4 3rd
4 Bhalukjuli 11 6 1 3rd
5 Bahbari 7 3 1 3rd
6 Bogajuli 6 4 2 3rd
7 Daijima 12 3 2 3rd
8 Dirang 8 4 2 3rd
9 Bhumki 6 4 2 3rd
10 Turkuni 5 3 1 3rd
11 Buradiya 19 11 5 1 4th
Kaldiya basin 109 56 25 1 5th
Source : Counted by the researcher from the toposheet of scale 1:63360
81
82
While considering the number of stream segments it is observed that the
maximum number of stream segments are associated with the Buradiya river followed
by the Moradiya river, Deojara river, Bhalukjuli river and Jorabari river because of
their catchments largely lying over high lands. The developments of these drainages
are naturally systematic with the efficiency of carrying water and debries in the high
lands. The other streams flowing partly over the plains have their comparatively less
number of stream segments. The surface drainage system is not well developed due to
smooth relief and relatively low rainfall. Hence, the number of streams are not found
in proportion to the orders.
4.1.3 Bifurcation Ratio
The bifurcation ratio *(Rb) being the ratio between any order of stream
segment to the next higher order of stream segment in a basin, is one of the important
characteristics and also and indicator of analysis. It gives an effective idea in
analyzing the basin form and the processes as well working on it. The bifurcation
ratio is related to the branching pattern of the drainage network. The study of
bifurcation ratio in different places indicates marked seasonal variations due to the
differences in climatic conditions, geological and structural characteristics, lithology,
relief feature and stage of basin development.
Horton (1945) recognized bifurcation ratio as one of the most important
characteristics of the drainage basin. He has postulated that bifurcation ratio varies
from 2.00 in the flat or rolling basins and 3.00 to 4.00 in the highly dissected
mountainous basins.
Strahler has observed that the bifurcation ratio is a dimensionless property of
an ideal drainage basin, because drainage system in topographically and structurally
homogenous materials tends to display geometrical progression. It is not surprising
that the ratio shows only a small variation from region to region.
* b
u
u
RN
N=
+1 Where,
Rb = Bifurcation Ratio.
Nu = Number of streams of a given order.
Nu+1 = Number of streams of the next higher order.
83
The bifurcation ratio of all the eleven small basins have been calculated and
the same have been represented in the table 4.2
Table 4.2 Kaldiya Basin : Bifurcation Ratio (Rb)
Sl.
No. Name of the Sub-Basins
Bifurcation Ratio Average
Bifurcation
Ratio (Rb) N1/N2 N2/N3 N3/N4
1 Deojara 1.28 2.33 1.81
2 Jorabari 1.67 3.0 2.34
3 Moradiya 3.2 1.25 2.23
4 Bhalukjuli 1.83 6.0 3.92
5 Bhabari 2.33 3.0 2.67
6 Bogajuli 1.5 2.0 1.75
7 Doijima 4.0 1.5 2.75
8 Dirang 2.0 2.0 2.0
9 Bhumki 1.5 2.0 1.75
10 Turkuni 1.67 3.0 2.34
11 Buradiya 1.72 2.2 5 2.97
Kaldiya Basin 2.41
Source:Morphometric data computed by the researcher from the topographical sheets.
Though the Tihu river is a fourth order basin and tributary to the Kaldiya river
system, it is not included in the study. It is because that the Kaldiya river has been
famous in its own identity and name. The average bifurcation ratio of eleven sub
basins of Kaldiya basin confirms the observations of the geomorphologists. The ratio
ranges from 1.75 to 3.92 in the basin. The Bhalukjli and Doijima basins have the
ratios of 3.92 and 2.75 respectively and the ratios that both the basins are having their
branches in the dissected region. The other basins are located in the flat plain. The
average bifurcation ratio of the basin as a whole is 2.41 (Table 4.2)
However, as evident from the computed values, the sub-basins under study do
not show constant values of bifurcation ratio. This is because of the basin’s variability
of structural control on the drainage network in its different parts. The bifurcation
ratio in the Kaldiya basin varies from a minimum of 1.75 in case of drainage basins
having their existences in topographically flat to slightly rolling areas to around 3.0 in
the drainage basin’s high land areas.
84
The general trend of bifurcation ratios confirm with the above hypothesis
because there is a general trend of decrease in the bifurcation ratios. Gensti and
Scheneider (1965) have further propounded that basins of equal order but variable
areas tend to have the smallest bifurcation ratios in the smallest areas, the ratio
increases with increasing areas up to a certain size beyond which the bifurcation ratios
tend to become constant. This hypothesis can be applied to the four small basins, viz.
Doijima, Bhahbari, Bogajuli and Dirang. The mean, median and standard deviation of
the bifurcation ratio are 2.41, 2.34 and 0.59 respectively
4.1.4 Stream Length
The stream length is a significant morphometric parameter of the drainage
basin as it helps in the calculation of drainage density vis-à-vis the energy of the
streams. The stream lengths of different orders of all the basins have been measured
in kilometer and represented in Table 4.3. The total length of various orders have no
significance because they may not be compared. Therefore, mean lengths of each
order has been calculated. Thenafter all the average length values have arranged in
Table 4.4
Table 4.3 : Kaldiya Basin : Stream Length (Lu)
Sl.
No.
Name of
the Basin
Stream Length (Km.) Total Length
(Km.) 1st Order 2
nd Order 3
rd Order 4
th Order
1 Deojara 32.5 15.0 17.75 - 65.25
2 Jorabari 14.0 16.0 2.50 - 32.50
3 Moradiya 24.5 15.5 25.75 - 65.75
4 Bhalukjuli 11.0 13.0 3.5 - 27.5
5 Bhabari 7.5 4.5 1.0 - 13.0
6 Bogajuli 10.5 6.5 3.25 - 20.25
7 Doijima 6.25 3.5 4.0 - 13.75
8 Dirang 7.25 7.0 2.5 - 17.75
9 Bhumki 11.75 2.0 3.50 - 17.25
10 Turkuni 22.50 9.25 10.0 - 41.75
11 Buradiya 25.6 13.8 12.5 2.7 54.6
Source : Measured from the topographical map of scale 1:63360.
85
Table 4.4 : Kaldiya Basin : Mean Stream Length
Sl.
No. Name of the Sub Basin
Mean Stream Length (Km.) L1 L2 L3 L4
1 Deojara 3.61 2.14 5.91 -
2 Jorabari 1.4 2.67 1.25 -
3 Moradiya 1.53 3.10 6.43 -
4 Bhalukjuli 1.0 2.17 3.5 -
5 Bhabari 1.07 1.50 1.0 -
6 Bogajuli 1.75 1.63 1.63 -
7 Doijima 0.52 1.17 2.0 -
8 Dirang 0.91 1.75 1.63 -
9 Bhumki 1.36 0.50 1.75 -
10 Turkuni 4.5 3.08 10.0 -
11 Buradiya 1.35 1.25 2.5 2.7
Source : Calculated based on Table 4.1 and 4.3
Generally, the first order stream segments have the shortest mean length. On
the other hand the mean length increases with the increase in order. All the streams
follow this postulation except some departure in certain orders of a few streams
suffered with some sort of abnormality.
Table 4.5 : Kaldiya Basin : Cumulative Mean Stream Length
Sl. No. Name of the
Basin
Cumulative Mean Length (Km)
Up to 1st
order
Up to 2nd
order
Up to 3rd
order
Up to 4th
order
1 Deojara 3.61 5.75 11.66 -
2 Jorabari 1.40 4.07 5.32 -
3 Moradiya 1.53 4.63 11.06 -
4 Bhalukjuli 1.0 3.17 6.67 -
5 Bhabari 1.07 2.57 3.57 -
6 Bogajuli 1.75 3.38 5.01 -
7 Doijima 0.52 1.69 3.69 -
8 Dirang 0.91 2.66 4.29 -
9 Bhumki 1.36 1.86 3.61 -
10 Turkuni 4.5 7.58 17.58 -
11 Buradiya 1.35 2.60 5.10 7.8
Source : Based on Table 4.4
86
For example, the tributaries like Deojara, Moradiya, Bhumki and Turkuni are
the exception. The Deojara basin shows that the mean lengths of second and third
order are less than that of the first order. The Moradiya indicates that the lengths of
stream of third order is less than that of the other lower orders. The Bhumki basin has
also shown that mean stream length of the second order is higher than that of the third
order. Similarly, the Turkuni basin shows the mean length of third order streams is
less than that of the second order streams.
4.1.5 The Laws of Drainage Composition
Various compositions of a drainage basin have been found to play their roles
in shaping the morphological and hydrological behaviour of the basin concerned. The
Kaldiya Basin is no exception to it. In this context an attempt has been made to
examine the pattern of channel network and its influenciable basin areas as per the
Horton’s law of drainage composition (1945). Horton tried to explore hydrophysical
behaviour of a drainage basin following some major laws of drainage composition, in
terms of order, number, length and areas of drainages.
Table 4.6: Kaldiya River Basin : Stream Order-Number Relationship
Stream
Order
(u) =x
x2 Stream
Number
Nu = y
Log y x. Log y Estimated Stream
Number
Yc = a-bx
1 1 109 2.0374 2.0374 184.17
2 4 56 1.7481 3.4962 41.59
3 9 25 1.3979 4.1937 9.39
4 16 1 0 0 2.12
� � = 10 � �= 30
� �� �= 5.1834
� � �� �= 9.7273
Log y = a - b x
Where,
y = Number of Stream Segments
x = Stream Order
a and b are constant
Where,
a is the point of intersection and
b is the regression co-efficient or slope.
Source : Estimated by the researcher from the data collected from topographical sheet.
87
KALDIYA RIVER BASIN
STREAM ORDER – NUMBER RELATIONSHIP
Fig. 4.3
88
Horton’s (1945) law of drainage (order vs number) shows a negative
exponential relationship (Table 4.6). As order increases the total number of stream
segments of the higher order decreases. In the Kaldiya Basin the drainage network
corresponds to the Horton’s law. The Kaldiya Basin clearly shows that there is,
however, some deviation from the normal relationship between the drainage number
and order (Table 4.6 and Fig. 4.3). Such a deviation is observed on the distribution of
the points on the graph for first, second, third and fourth orders of streams. It is seen
that orders and numbers of the basin drainages are correlated with a co-efficient value
of -0.92 which signifies a high correlationship. However, as the r2 or regression co-
efficient is only 85 per cent, order vs number relationship in the Kaldiya Basin is seen
to have its less roles in the development and modification of hydraulic and
topographic situations. Since, in the foothill region, the first order stream segments
are more in number, erosional activity is also more. Thus, the topographic complexity
is more on this rugged terrain. On the other hand, number of stream segments
decreases with increases in order. This indicates less erosional functionability in the
low undulating topography of the basin. It can, in this context, be explained that the
channel planform and flow of waters on the Kaldiya Basin encounters often with
erratic situations (Barman, 1986).
Table 4.7 : Kaldiya River Basin : Stream Order-Stream Length Relationship
Stream
Order (u)
x
x2
Cumulative
Mean
Stream
Length
(CI), y
Log y x. Log y
Estimated
Mean Stream
Yc = a + bX
1 1 1.590 0.201 0.201 1.757
2 4 3.484 0.542 1.084 3.233
3 9 6.934 0.841 2.523 5.948
4 16 9.634 0.984 3.935 10.945
∑ � = 10 ∑ �� = 30 ∑ ��� = 2.568 ∑ �. ��� = 7.744
Log Y = a + bX
Where, y = Mean stream length
x = Stream order
a and b are constant
Where, a is the point of intersection, and
b is the regression co-efficient or slope.
Source : Estimated by the researcher from the data collected from topographical sheet.
89
KALDIYA RIVER BASIN
STREAM ORDER – STREAM MEAN LENGTH RELATIONSHIP
Fig. 4.4
Str
eam
mea
n l
eng
th (
C L� )
90
As analysis of the stream order vs stream mean length (Table 4.7 and Fig. 4.4)
shows that they are also highly correlated. Coefficient of correlation (r) is equal to -
0.98. It can further be explained that their functional relationship in the basin is
limited within 97 Percent. The plots on the graph for stream order vs drainage stream
mean length follows an upward trend. At the same time the relationship deviates more
from the normal, specially with 3rd
and 4th
orders of streams. The other orders are,
having deviations of lower values. The whole phenomenon indicates the anomalous
distribution of drainage net and proportion of length vis-à-vis geomorphic and
hydrologic actions and reactions as related to the drainages. The differences between
the topographic highs and lows have differential influences on the drainage net and
geomorphic development with the exiting pattern.
The orders and their respective basin areas (Table 4.8 and Fig 4.5) bear a high
correlation signified by a value of 0.96 where r2 is 94 percent. It clearly indicates that
as the order increases inclusion of new areas with input of water supply increases
progressively in the basin.
Table 4.8 : Kaldiya River Basin : Stream order vs Mean Basin Area Relationship
Stream
Order (u)
x
x2 Mean Basin
Area (Āu) Y
(km2)
Log y x. log y Estimated Mean
Basin Area
Yc = a + bx
1 1 0.65 -0.187 -0.187 0.474
2 4 2.26 0.354 0.708 2.518
3 9 6.46 0.810 2.431 13.366
4 16 119.46 2.077 8.309 70.958
∑ � = 10 ∑ �� = 30 ∑ ��� = 3.054 ∑ �. ��� = 11.261
Logy = a + bx
Where, y = Mean basin area
x = Stream Order
a and b are constant,
Where, a is the point of intersection, and
b is the regression co-efficient or slope.
Source : Estimated by the researcher from the data collected from topographical sheet.
91
KALDIYA RIVER BASIN
STREAM ORDER – MEAN BASIN AREA RELATIONSHIP
Fig. 4.5
92
4.1.6 Sinuosity Indices
A river or its channel is no way is straight in reality. But under certain
conditions it is called straight, meandering or braided, reticulated and anastomosing
etc. It is observed that meandering of stream exists as per natural rule (Davis, 1913) in
river environment and involves a natural state of affairs affected by gradual stages
related to channel departure from the straight (Tanner, 1968). The pattern value and
magnitude of meandering of river channels thus act as some of the most significant
and meaningful indicators of hydraulic geometry and development of the channel as
well as of the basin. This is mainly due to the hydrologic and fluvio-geomorphic
dynamics over space and time. There is a number of ways to analyse the pattern,
magnitude and dynamics of meandering of a stream. One of such ways involves the
adoption of the technique related to sinuosity index.
In general the ‘Sinuosity’ of a stream is the deviation of a channel from its
straight line between the source and mouth of the river concerned. The sinuosity of
the channel is expressed by an index called the sinuosity index which is defined as the
ratio of the channel distance to its axial distance (Chorley 1969). According to
Mueller (1968), sinuosity index is expressed by S.S.I. (Standard Sinuosity Index)
which is nothing but the ratio of a channel length (CL) and the valley length (VL). He
also introduced ‘Topographic Sinuosity’ (T.S.I.) and ‘Hydraulic Sinuosity’ (H.S.I.)
indices as the measures of topographic and hydraulic influences on the meandering
pattern of a channel. The river courses are classified into three categories on the basis
of the Standard Sinuosity Index viz. (i) Straight river course (S.S.I.=1.00), (ii) Sinous
course (S.S.I.=1.00-1.50) and Meandering course (S.S.I. ≥ 1.50). The Kaldiya river is
influenced by, as observed in the field and on map, topographic and hydraulic
conditions while developing meandering pattern at its different reaches. Table 4.6
indicates the measures of T.S.I., H.S.I. and S.S.I. on different reaches of the channel
of the Kaldiya river.
The table 4.9 reveals perceptible variations of sinuosity indices at different
reaches, viz., upstream, middle stream and downstream locations.
93
Table 4.9 : Kaldiya River : Sinuosity Indices at different Reaches
Segment
of
stream
or
reaches
Air
length
in km
(AL)
Channel
length
in km
(CL)
Valley
length
(VL)
Channel
index
(CL/AL)
Valley
index
(VL/AL) Hy
dra
uli
c
sin
uo
sity
in
dex
��−
����
−�×1
00
To
po
gra
ph
ic
sin
uo
sity
in
dex
��−
���
−�×1
00 Standard
sinuosity
index
CL/VL
Upper
reach 11 16.75 15.12 1.52 1.37 29% 71% 1.11
Middle
reach 13 19.90 16.50 1.53 1.27 49% 51% 1.21
Lower
reach 21 32.62 26.32 1.55 1.25 55% 45% 1.24
44% 56% 1.19
Source : Generated by the researcher from the data derived from the topographical map.
The upper reach represents a low value of S.S.I. (1.11). On the other hand, the middle
and lower reaches show medium (1.21) and moderately high (1.24) standard sinuosity indices.
So far the T.S.I. is concerned, the channel marks an index of 71.0 per cent for its upper reach.
The middle reach of channel has the T.S.I. marked at 51 per cent, whereas the lower reach
records a percentage of 45.0 as T.S.I. The H.S.I.s of the channel for different segments of the
channel are also calculated. The upper part of the channel has an index value of 29 per cent,
whereas the middle and the lower reaches are marked by H.S.I.s of 49 per cent and 55 per
cents respectively.
The pattern of estimated sinuosity index for the Kaldiya river at its different reaches
reveals differential fluvio-geomorphic developments. The low value of S.S.I. in the upper
reach of the river shows that the river channel in the foothill part is straight enough. There
exist meanders with perceptible amplitudes and wave length in the middle reach as revealed
by medium sinuosity index of 1.21 (Table 4.9). This is mainly because of presence of
compact built up plains where channeling of the river is controlled by the plains. Contrary to
this, the lower reach of the channel indicates moderately high standard sinuosity index. A
close analysis of the distributional pattern of S.S.I.’s conforms that there are varying
influences of topographic determinants and hydraulic forces along the river Kaldiya. Still
then, the river is not much meandering as revealed by the sinuosity indices.
As the upper reach of the Kaldiya river falls on Bhutan hills and foothills
characterized by high slope over the areas of hard rocks, there develops straight channel
course of low S.S.I., moderately high T.S.I. and low H.S.I. (Barman, 1986, p-159). Again, in
the middle reach, the S.S.I. is higher (1.21) than that of the upper reach. As a result, hydraulic
action that can be expressed by H.S.I. is slightly above medium order (60 per cent) and the
94
T.S.I. is below 50 per cent. So far the lower reach is concerned, one can observe dominance
of hydraulic action (40 per cent) over the topographic influences measured by T.S.I. of 45 per
cent. The overall situation is such that the whole of the Kaldiya river is marked by H.S.I. of
44 per cent, T.S.I. of 56 per cent and S.S.I. of 1.19.
The hydraulic and topographic sinuosity indices (HSI and TSI) are the
valuable morphometric tools which help in determining the stages of the basin
development as well as the controlling factors of sinuosity. It is thus observed that the
topographic features in the Kaldiya Basin reflect matured to late matured stages of
development.
4.2 Areal Aspects of the Basin
The area of a basin is a significant morphometric parameter affecting the
spatial distribution of a number of morphometric attributes and controlling factors
such as drainage density, drainage texture, stream frequency, slopes, dissection index,
circularity ratio, etc. Anderson (1957) termed the basin as a ‘devil’s own variable
because almost every watershed characteristics is correlated with area’. The first order
basins have the smallest mean basin areas and the successive higher orders show
increase in the areas culminating in the largest area of the highest order of the trunk
stream. The areas of the eleven small basins in the Kaldiya river basin are measured
with the help of planimeter and shown in the Table 4.10
Table 4.10 : Kaldiya Basin : Sub-basins Wise Area and Perimeters
Sl.
No.
Sub Basin
Name Area (Km2) Basin Perimeter
1 Deojara Nadi 62 42.50
2 Jorabari Nadi 6 26.25
3 Moradiya Nadi 68 105.00
4 Bhalukjuli Nadi 16 15.50
5 Bahbari Nadi 8 11.25
6 Bogajuli Nadi 12 14.25
7 Daijima Nadi 7 15.00
8 Dirang Nadi 16 18.00
9 Bhumki Nadi 19 15.75
10 Turkuni Jan 69 45.25
11 Buradiya Nadi 52 41.35
Source : Based on the data collected from topographical sheets of scale 1:63360.
95
4.2.1 Basin Perimeters
The areas of the drainage basins are delineated by watersheds which are
termed as basin perimeter. The perimeter of a basin can be directly correlated with the
square root of the basin area. The increase or decrease in the basin perimeter depends
upon the increase or decrease respectively of the basin area (Table 4.10)
In a basin perimeter is positively correlated with channel length. The perimeter
increases with increase in channel length and the former decreases with the decrease
in the latter. The area and perimeter of a basin and the length of channel in the basin
have been the significant morphometric variables which determine the shape, size and
genetic as well as generic aspects of a drainage basin.
4.2.2 Drainage Density
The density of stream network in a basin has long been recognized as
topographic characteristics of fundamental significance. This arises from the fact that
the network density is a sensitive parameter which in many ways provides the link
between the form attributes of the basin and the processes operating along the stream
course. If drainage basins were uniformed in every aspect, stream flow would be
proportional to the length of water course in a basin because channel flow is much
more rapid than the alternative flow on or beneath the slopes. As the extent and
density of the network reflect topographical lithological, pedological and vegetational
controls and because they incorporate the influence of man, network density promises
to be a valuable index.
Lithology, climate and vegetation cover are the major factors for the varying
density. Infiltration capacity of soil or surface layer is also an important factor which
is directly affected by lithology and all are closely related to climate. Chorley (1957)
and Chorley and Morgan (1962) compared three lithologically similar areas from
Britain and confirmed a close relationship between drainage density and rainfall.
Horton defined drainage density as a ratio of total length of all streams
segments in a given drainage basin to the total area of that basin. Drainage density is
the quotient of the total length of all the streams and the total drainage area.
96
Drainage density *(Dd) is expressed in terms of length of streams per unit of
area. For the convenience of the present study the entire Kaldiya Basin is marked by
grids of 2.54 cm x 2.54cm on 1:63,360 topographical map. Thereafter the data
computed by adopting Horton’s method of drainage density are tabulated (Table
4.11). Isolines are then drawn at density interval of 1Km./ Km.2 to have an isopleth
map (Fig. 4.6)
Table 4.11 Kaldiya Basin : Areas Under Drainage Density Groups
Drainage Density
group (Km/Km.2)
Total Area (Km.2)
Percentage of area
to basin’s total
Drainage Density
category
< 1 42.72 8.49 Very low
1 – 2 208.43 41.43 Low
2 – 3 106.67 21.20 Moderate
>3 145.20 28.88 Moderately high
503.00 100.00
Source : Data compiled by the researcher based on the topographical sheets of R.F.
1:63360.
The Kaldiya river basin occupying an area of 503.00 Sq. kms and the Dd
values of the grids have been derived and the same have been grouped as moderately
high, moderate, low and very low. It has been apparent that the drainage density of the
aforesaid basin ranges between less than 1 and above 3. Their values are grouped into
below 1, 1-2, 2-3 and above 3. (Table 4.11)
The low category of Dd occupies the maximum of 41.43 percent of the total
area of the basin, while the very low category occupies only 8.49 percent of the total
area. The moderately high drainage density is found in the middle and south western
corner of the aforesaid basin and it occupies 28.88 percent of the total area. The
moderate density occupies only 21.20 percent of the total area. (Fig. 4.6)
* d
u
u
DL
A=∑
∑ Where,
Dd = Drainage Density
L u∑ = Total lengths of all segments
A u∑ = Total area of the basin
97
98
The variation in drainage density has been related to precipitation
effectiveness, vegetation cover, permeability of terrain, climatic character and also to
structure, particularly rock type.
A rise in drainage density occurs with increasing relief. This is clear from the
work of Doornkamp and King (1971). It is interesting that Peltier (1962), in a pilot
study, found that there was a much steeper rise in drainage density with increasing
mean slope in tropical areas than any other climatic zone.
The mean value (2.28) of drainage density falls in moderate drainage density
group. The standard deviation which is 0.10 stands at very low drainage density
group. The area below the mean accounts for 71.12 per cent or 357.82 km2 and above
it the area is 145.20 km2 equivalent to 28.88 per cent
4.2.3 Stream Frequency
The stream frequency like drainage density is also one of the most important
morphometric parameters of the drainage basin. Horton (1945) introduced stream
frequency (or drainage frequency, Fs) as the number of stream segments per unit area.
Stream frequency is calculated by the total number of streams in a drainage basin
divided by the area of the basin, or the stream frequency is calculated by the total
number of streams in a unit area in a given drainage basin.
For determination of stream frequency Hortonian formula, FS=(N/A), where
FS is the frequency of stream, N is the total number of streams and A is the area of the
basin or region is adopted for the present work. For the convenience of study, the
entire Kaldiya basin is transformed to 2.54 cm x 2.54 cm (or 1 inch) square grids on
one inch to a mile (1:63,360) topographic sheets. A general overview of the frequency
distribution of drainage net of the basin indicates high to low frequency as one moves
from foothill zone to the flood plain Table 4.12 and Fig. 4.7 show the spatial pattern
of drainage frequency distribution and thereof areas under different frequency groups.
These values are classified here into very low, low, moderate and high groups.
Then an isopleth map is drawn to the show the groups. The resulting map of the
stream frequency brings out the spatial variation clearly.
99
Table 4.12 Kaldiya Basin : Areas Under Stream Frequency Groups.
Stream frequency
N/A Area (Km
2)
Percentage of area
to the basin’s total
Category of
frequency
< 3 207.87 41.32 Very low
3 – 5 175.32 34.85 Low
5 – 7 96.24 19.15 Moderate
> 7 23-58 4.68 High
Total area 503.00 100.00
Source : Based on data generated by researcher from topographical sheets.
It is clear from the Table 4.12 that there is decreasing tendency of areas and
percentage shares as stream frequency category increases from very low to high. The
very low category of frequency accounts for 41.32 percent equivalent to 207.87 km2
of the total area of the basin, while low, moderate and high categories cover 34.85
percent or 175.32 Km2, 19.15 percent equivalent to 96.24 Km
2 and 4.68 percent or
23.58 Km2 respectively. The high group is found as a patche in the basin.
The mean value of the stream frequency for drainage net of the basin is 3.74,
which fall in the low category of the frequency. The standard deviation is 0.24. Below
the mean, the area occupied is about 76.17 per cent or 383.19 km2 and above the
mean there lies 23.83 per cent of the basins area equivalent to 119.82 km2
The study of the Fig 4.7 reveals that the frequency of stream in the Kaldiya
river basin depends upon a number of variable factors, which may be divided into two
categories.
1. Natural Factors.
2. Map Factors.
Natural factors
The important factors which affect and effect the stream frequency of the
basin are as follows. The relative significance of these factors varies from place to
place.
a) Climate.
b) Lithology and structural characteristics of rocks.
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101
c) Relief and slope.
d) Infiltration capacity of soil and surface layer and
e) Vegetation.
Climate plays a very important role in the basin so as far as the stream
frequency is concerned. The average annual rainfall (ranging between 1680 to
2400mm) and the number of rainy days around 186 days are quite adequate in this
basin. Thus, it is the climate of this basin which accounts much for the development
of the drainage system in this basin, thereby giving rise mostly to moderate and high
stream frequencies.
The relief and average slope play very significant role in the genesis and
development of stream frequency in this basin. Drainage lines will develop in large
number upon an irregular surface than upon one which lacks conspicuous relief. It
will be seen from the relief map (Fig. 3.1) of the basin that the relief is moderate in
the central area and it decreases to the southern part. The central part shows moderate
slope in large areas which explains the coarse stream frequency in this area. It is
interesting to find that wherever the average slope is low, the stream frequency is also
more or less low. In the foothill areas slope and relief being high there has been
apparently high drainage frequencies.
According to Thornbury, Horton has called infiltration capacity, or what is
more commonly reffered to as the permeability of the mantle rock and bed rock, is
probably the most important single factor influencing the drainage texture. Here, the
basin has shown less amount of percolation and this has resulted in the moderate to
high stream frequency.
Technical factors
The most important technical factors involved in determining the stream
frequency are the scale of the map and the accuracy of mapping. Needless to mention
that with large- scale maps one may get a more accurate picture of drainage frequency
than from small scale maps. In this study the author has used the topographic sheets of
the scale 1:63,360 due to the lack of larger scale topographic sheets. The aerial
photograph gives a better picture of stream frequency which is not available in this
area due to restriction. However, for the work of certain correction method is applied
to minimize the error.
102
4.2.4 Drainage Texture
Drainage texture is the most promising and useful variable in the
morphometric analysis of drainage basin, because it is related to the dynamic nature
of the network of the stream segments and the area of the basin. This variable,
therefore, can be fruitfully used for the classification of drainage basin in order to
have processes and to the interpretation of temporal changes of the drainage network
in the Kaldiya basin. It may be regarded as dependents on climate and catchment
characteristics.
An important geomorphic concept is drainage texture, by which we mean the
relative spacing of drainage lines. Horton (1945) defines drainage texture on the basis
of stream frequency (number of stream per unit area). In fact, the term texture has
been used loosely and no success has been made to search out a quantitative
parameter for its calculation. According to Savindra Singh (1976), ‘the term texture
must be used to indicate relative spacing of the streams in a unit area along a linear
direction’.
For the purpose of the present study the basin is divided into grids. Then the
numbers of stream crossing along both the diagonals are counted and averaged.
Further the number of stream crossing should be calculated per km length on the basis
of the following formula which is given by Savindra Singh. The quotient of the unit
length (1 km) and numbers of stream crossing would be the average spacing of the
stream per km length. The data so derived may be classified into fine, moderate,
coarse and very coarse. But the qualifying data for the classification may vary
according to the scale and magnitude of grid square simultaneously the ratio may
remain the same.
Table 4.13 : Kaldiya Basin : Areas under Drainage Texture Groups
Drainage Texture
(spacing of stream
per km of length) Area (km
2)
Percentage of area to
the basins total Texture category
0.2 – 0.4 163.62 32.53 Fine
0.4 – 0.6 286.71 57.00 Moderate
0.6 – 0.8 36.51 7.26 Coarse
0.8 – 1.0 16.15 3.21 Very coarse
503.00 100.00
Source : Data compiled by the researcher from the Topographical Sheet.
103
104
On the basis of the formula, the minimum and maximum values come to 0 and
1. Four classes of fine (0.2-0.4), moderate (0.4 – 0.6) coarse (0.6 – 0.8) and very
coarse (0.8 – 1.0) at uniform class interval have been worked out. The moderate
texture which secured first position covers 57 per cent of the areas of the basin. On
the other hand, very coarse category occupies only 3.21 per cent of the area of the
Kaldiya basin Table 4.13 and Fig. 4.8).
The spatial variations of texture in the basin are due to a number of factors.
Climate, vegetational cover, infiltration capacity (permeability of the rock and bed
rock) and geologic structure are significant controlling factors of drainage texture.
4.2.5 Circularity Ratio
It is the ratio of circumference of a circle constructed with same area as the
basin covers to the perimeter of the basin. Miller (1953) used this concept and method
of circularity for the first time which is similar to the elongation ratio. The index
values range around 1. The highest values of this basin indicates that the basin is the
largest compared to other basins.
Circularity index as ratio deals with the ratio of the drainage basin area (Ab) to
the area of a circle having the same perimeter. It is a quantative approach to compare
precisely, area of the actual form of the drainage basin to the area of the circle
encircled by the perimeter of the same drainage basin. High, medium and low values
of basin circularity are correlated with stages of the drainage basins.
Table 4.14 (a) Kaldiya Basin : Sub-basin wise Circularity Indices.
Sl. No. Name of the Sub-Basins Circularity Indices
1 Deojara 0.43
2 Jorabari 0.55
3 Moradiya 0.39
4 Bhalukjuli 0.51
5 Bhabari 0.84
6 Bogajuli 0.62
7 Doijima 0.88
8 Dirang 0.69
9 Bhumki 0.54
10 Turkuni 0.36
11 Buradiya 0.45
0.57
Source : Data compiled by the researcher from the Topographical Sheet.
105
It is apparent from the Table 4.14 (a) that the Circularity ratio varies from 0.36
to 0.88 in the sub-basin of the Kaldiya river basin. The average circularity ratio of the
entire basin is 0.57. These circularity indices are classified into three categories viz.
High (> 0.80), Moderate (0.50 – 0.70) and Low (< 0.50) (Table 4.14 b).
Table 4.14 (b) : Kaldiya Basin : Circularity Indices with Stages.
Circularity Indices Number of
Drainage Basin
Category Percentage of Total
Area
>0.80 2 High 13.75
0.50 – 0.80 5 Moderate 46.84
< 0.50 4 Low 39.41
Source : Data compiled by the researcher from the Topographical Sheet.
The five sub-basins out of eleven have attained the moderate category, while
two sub-basins viz. Doijima and Bhabari have attained high category. The remaining
four sub-basins viz. Deojara, Moradiya, Turkuni and Buradiya have attained the low
category.
�� = ���
Where, C. I. = Circularity Index.
Ab = Drainage Basin Area.
Aa = Area of a circle having the same perimeter.
106
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