International Journal of Interdisciplinary Research in Science Society and Culture(IJIRSSC)
Vol: 1, No.:1, 2015
ISSN 2395-4335, © IJIRSSC
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Causes of Change of River and Landform Characteristics in the MutangaNona River Basin, Assam
1
Anjan Kumar Talukdar
2
Ratneswar Barman
1
Assistant Professor , Department of Geography
Narangi Anchalik Mahavidyalaya, Narangi, Guwahati-171, Assam
2
Professor (Rtd),Department of Geography, Gauhati University
_________________________________________________________________________________
ABSTRACT : River channels, big or small, along with their network in a basin are neither at
all static nor permanent even as they are persistent. Likewise the landforms developed due to
fluvial processes of rivers and their network are also not static. Such changes of river
landform and planform as well are different in different areas and time. The Mutanga -Nona
basin located in the Brahmaputra valley below the steeply rising Bhutan Himalaya have
rendered appreciable changes of the basins channel network and characteristic fluvial
landforms specially after the 1897 great earthquake and more so after the 1950 great
earthquake. During the last 100 years or so the river Mutanga -Nona has got drastic changes
due to secular endogentic process of earthquake and fluvial processes entangled in
sedimentation, flow of water and many others.The basin is least studied in respect of its
fluvio-geomorphic history of channel network changes and characteristic landforms
development.
Keywords: Channel network, persistent, metamorphosis, sedimentation, river plan form,
channel shifting.
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I. Introduction:
It has been observed that river channels, big or small, along with their network
in a basin area are not at all static nor permanent even as they are persistent [1].
Similarly the landforms developed out of the influences of them are not static; rather
they are continually modified due to a number of causes included in climatic to
hydrologic factors through topographic ones. However, the persistency differs from
place to place and time to time. The rivers in a valley or basin characterized by high
rainfall are highly unstable and, therefore, changes of channels and network are very
frequent and the landforms are also largely changing ones and the river
metamorphosis [2] is more common. The Mutanga-Nona river is of this type.
II. Objectives of the study:
1) To
evaluate the river planform
2) To study the fluvio-geomorphic landform characteristics.
3) Investigate their causes of development.
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III.Study Area:
The Mutanga-Nona river basin (fig. 1) conforms to a major tributary basin of the
Baralia river basin in the Brahmaputra valley below the steep Bhutan Himalaya. This
basin extending latitudinally from 26 0 N to 26 0 53 / 3 // and longitudinally from 91 0 29 /
to 91 0 37 / 30 // E covers a catchment area of 338 km 2 . The Mutanga-Nona basin has
undergone appreciably significant changes of its channel planform along with
landform specially after the 1897 great earthquake and more so after the similar great
earthquake of 1950. Even as the basin is flat enough, there are o ther factors of
changes of channel network and its planform along with the basin’s characteristic
landforms.
Figure 1: Study area – Mutanga-Nona river basin
IV.Methodology :
The Study is based on empirical method of investigation. The entire research work is
framed and categorized within the definite and precise stages one after another. At the
beginning the problem is formulated based on reading of different books, journals, newspaper,
etc. Personal experience and interest along with discussion with other persons have helped in
the selection and formulation of the research problem.
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In this study, a number of base materials are collected and compiled as data base. The
base map of the basin has been prepared from the Indian Topographical Sheets of 1:63,360
and 1:50,000 scale. Satellite images of 1988 and data from Google Earth imagery 2014 are
also used for the purpose. Geological accounts and information of the basin have been
collected from the geological survey of India, from the different base map. The necessary
morphomatric data base have been generated from different topographic maps and imageries.
In the second phase of the work, the proper field-works and observation are conducted
for the collection of primary data and information. Data were also collected from some
sources based on interview about history of flood, earthquake and changing pattern of
channel, etc. In the third stage, the study basically deals with the processing of raw data into
some tables, index forms, etc. Maps, diagrams, graphs, digital models etc. were then drawn
with the processed by data using some statistical, simple cartographic mathematica land
hydrological techniques on the processed data which are found relevant to fluvio
geomorphological study.
In the fourth or the final stage, the tables, maps, diagrams, field ideas, photographs etc.
were arranged systematically and their analysis and explanation are done to write up the
thesis.
V. Result and Discussion :
a) Causes of changes of river plan form and river network
This paper generally deals with the major causes of change of river network and
landform characteristics in the Mutanga-Nona river basin. It has been observed that
the channel network of the Mutanga-Nona had changed its pattern through time and
space, specially since 1911-13 onwards. It would be clear from this study about the
changed pattern of channel network of the Mutanga river in the purview of
geomorphic and hydrological processes which had later been responsi ble in capturing
the course and channels of the Mutanga-Nona river. Now the combined river network
and plan form is regarded as the Mutanga-Nona river basin. There are a number of
causes responsible for such changed characteristics of the river channels ne twork.
Frequent earthquakes, high sedimentation and flow of water, etc. have been
recognized as the prime factors. Other factors like channel gradient, relief or slope of
the valley wall, channel pattern etc. have also been playing roles in changing the
channel plan forms.
i.
Earthquakes
Earthquakes have been modifying the landform and river configuration of the
basin. The present study area, i.e., the Mutanga-Nona Basin along with the entire
Himalayan mountain belt forms some earthquake prone areas. The nort h-eastern part
of India has been worst affected by earthquakes. Records of several earthquakes
available in seismological centres at various places in North -East India have revealed
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that four or five tremors occur in this region every year. However, substa ntially
significant earthquakes occur in this part with a gap of about 10 years, while a high
magnitude earthquake takes at an interval of about 50 years. Since the 16 th century
A.D. remarkable earthquakes in North-East India had occurred during 1558, 1596,
1642, 1663, 1669, 1676, 1714, 1869, 1875, 1897 (M = 8.7), 1918 (M = 7.6), 1923,
1930 (M = 7.1) and 1950 (M = 8.7) [3]. After 1950 there has not occurred any
earthquake having magnitude 7.0 or more. It is added that the frequency of occurrence
of earthquakes in N.E. India has decreased since 1969 [4] over the past frequencies.
Recent studies have revealed that during 1920-1969, the Brahmaputra valley itself had
suffered from 416 earthquakes (Irrigation and Flood Control Department., Govt. of
Assam). Fig. 2 gives an idea of influence of earthquakes in the region including the
present study area.
Fig 2 Seismicity in India and adjacent countries
The 12 June Earthquake of 1897
This was a severe earthquake felt in the region. Oldham [9] has given a
comprehensive review of this earthquake, while an excellent summary of it is given
th
by Davison (1936). The epicenter was located partly in the Shillong Plateau and
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partly in the plains of the Brahmaputra Valley [5]. This earthquake was felt over the
area bounded by the isoseismal line of V or VI[6]. The earthquake lasting for two and
half minutes affected an area of about 3,84,000 km 2 . The hills were raped and there
caused landships. There occurred fissures in the plains and riddled with vents, from
which sand and water poured out in most of the channels of west Assam. The
earthquakes of 1897 caused enormous damage of land surface, the embankments were
fissured, bridges and railways were broken and the permanent way was much cut up
by fissure. Nalbari and adjacent region including the Mutanga-Nona basin suffered
severely from this earthquake which altered the waterways and rendered them
impossible for boats to come up to Chawlkhowa from Barpeta – a route that was
formerly opened for boats. The destruction and change of course of river network
configuration were most evident in the Pagladiya, Baralia and Puthimari catchments
covering the basin under study. The landslide on the foot -hills of Bhutan yielded loses
materials to be carried by subsequent high floods as sediment towards the Mutanga
along with the rivers of this part. As a result, the river bed became braided in its
channels. The braided channels were most active in lateral shifting. So the Mutanga
gradually used to shift towards west and ultimately to join with the Nona to form the
present network pattern of Mutanga-Nona river.
The 2 nd July Earthquake of 1930
This earthquake is known as the Dhubri earthquake. Its epicenter was at a point
of latitude 25 0 5 / N and longitude 90 0 E. This earthquake of magnitude 7.1 was felt over
an area of about 8,96,000 km 2 . The earthquake had also some effect upon the network
configuration of the study area.
The 15 th August Earthquake of 1950
On August 15, 1950 another severe earthquake was felt in this region. The
epicenter of this earthquake is said to be located at 29 0 N and 97 0 E. The earthquake
affected the Mutanga-Nona basin causing landslips and rockfalls along the foothills of
the basin. The beds of the north bank tributaries rose up. This happens particularly in
the case of the Pagladiya, Nona and Puthimari rivers. In this part the beds got up by
0.61 to 0.92 m [7].
From the above discussion it can be argued that the sensitivity of drainage basin
to seismic disturbances particularly to 1897 and 1950 great earthquakes has caused
major changes of the Mutanga-Nona river’s channel network. Fig. 3 shows the change
of river network during the last 77 years. The changes are based on Indian
topographic maps of 1911-13, 1954-60 and IRS 1A LISS III satellite image of 1988 –
all being of R.F. 1:50000
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ii.
Sedimentation
The Mutanga-Nona River indicates that suspended sediment ranges from 0.23
Ha.m. in 1978 to 7.38 Ha.m. in 1988 within 22 years of record at Bilpar gauge site
(table 1). The yearly mean and median of suspended sediment loads are estimated
respectively at 1.80 and 1.15 Ha.m. The value of standard deviation is 1.95 Ha.m. It is
also revealed that suspended load increases with the increase of annual runoff. The
relationship between runoff and suspended sediment shows a high positive correlation
co-efficient (r) of 0.88. It implies that intensity of sedimentation at flood flow time is
high enough.
Fig 3: Changes of river network; Mutanga-Nona river basin[
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Table 1: Total annual runoff and suspended sediment load, Mutanga-Nona river
at Bilpar Gauge site, 1971-92.[10]
Year
Total Annual
Runoff
(Ha.m)
Total Annual
Suspended
Sediment
(Ha.m)
Year
Total Annual
Runoff
(Ha.m.)
Total Annual
Suspended
Sediment
(Ha.m)
1971
19477.16
4.83
1982
17580.31
1.19
1972
28180.30
6.10
1983
13354.98
0.79
1973
9329.83
0.59
1984
16362.48
1.87
1974
19817.86
1.12
1985
14292.55
1.05
1975
12286.16
0.65
1986
7004.23
0.37
1976
9945.24
0.53
1987
21337.29
2.62
1977
20505.92
1.24
1988
49883.83
7.38
1978
7567.30
0.23
1989
18429.37
1.77
1979
12110.00
0.43
1990
26591.44
3.37
1980
15308.00
0.57
1991
18701.21
1.53
1981
8339.00
0.27
1992
12709.45
1.17
Source : Based on data collected from Flood Control Deptt., Govt. of Assam.
The thickness of sediment deposits towards eastern embankment in both the
locations of railway bridge and N.H. 31 crossing point ranges from 2.4 m to 2.6 m
above the agricultural field. Similarly the western bank near Singimara has sediment
deposit having thickness of about 3.08 m above the Singimara beel. Deposits of only
1.70 m thick took place in its eastern bank. The river banks or embankments have
breached hither and thither because of heavy sediment deposits on river bed, low land
gradient and gentle slope of the river bed. Sediment deposits at the rate of 0.05 m per
year over the river bed have been estimated to occur on the above mentioned area.
Thus the high sediment deposits (bed load and suspended load) and flood waters have
changed the channel network configuration through time and space in the Nona river
channel.
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Table 2:
Thickness of sediment deposits at river bed above agricultural
field, near Bilpar and Singimara, Mutanga-Nona river basin.
Thickness of
Average Thickness
Sediment (in m)
of Sediment in (m)
3.20
Near Railway bridge towards Western
3.25
3.13
Embankment at Bilpar
2.95
1.50
Near N.H. 31 Western Embankment
1.65
1.72
Breah point, 1997
2.00
2.85
Near
Railway
bridge
Eastern
2.37
2.40
Embankment of Bilpar
1.98
2.15
Near N.H. 31 at Eastern Embankment of
3.05
2.62
Bilpar
2.65
2.75
At Singimara in Western Embankment
3.00
3.08
breach poin, 1988
3.50
2.15
At Singimara in East bank
1.75
1.70
(no Embankment)
1.21
Source: Based on field observation by the authors, 2007.
iii.
Flow of Water
The water flow at high, average and low levels of discharges in Bilpar gauge
site indicates appreciable fluctuation. The study of high, average and low discharge
levels at Tamulpur gauge site shows a regular trend of flow fluctuation where
maximum discharge gets varied within 98 m 3 sec -1 and 65m 3 sec -1 respectively on
1987 and 1993. The stage and discharge hygrographs have shown much of
irregularities in fluctuation of water and flood levels at Bilpar and Tamulpur cross sections. Table 1 reveals the total annual runoff pattern during 1971 to 1992 at Bilpar
site. A comparison of the runoff variation would clear the fluctuation of water flow.
The maximum runoff is computed at about 49883.83 Ha.m. during 1998 great flood,
while the minimum runoff was 7004.23 Ha.m. in 1986. The respective mean and
median runoff have been calculated at 17232.36 and 15835.24 Ha.m. with a S.D. of
14501.90 Ham. during this study period.
From the above discussion it is opined that the flow of water has a significant
effect upon the channel network pattern. The flow or runoff variation has a direct
Location
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impact upon hydrological parameters such as width, depth, velocity of water in the
basin and the alignment of the new channels as well. So, the river hydro -dynamic
forces have changed the channel pattern. The frequently occurred variation of flow
even within the rainy period caused by high rainfall variability makes the channels
unstable to effect bank erosion, channel migration, etc. and aggravate flood condition
and land deformation as well.
b) Changes of landform characteristics
The landform changes in respect of forms, process and stage are considered
here. The idea of landform change can be related to the energy of rivers along with
others like topographic inputs. Increase or decrease of river energy could be
controlled by a number of factors. These might change base level, runoff or even the
climatic derivatives after a long time. In 1965 an important contribution to the
development of landform as a function of time and space (area) was made by Schumm
and Lichty. The change of landform development depends upon the length of the time span. If there is no major uplift, the land is rapidly worn away and the surface
continually lowered towards base level. Over a long period of cyc lic time, landform
slowly gets loss of energy and mass that reduce altitude. However, if the period is
greatly reduced, some streams, or parts of stream in a drainage network and the slope
on them may be regarded to stay at grade or in a stage of dynamic e quilibrium. During
the period of graded time minor fluctuation may occur. As a result, for instance cyclic
variation in rainfall may cause consequent cyclic changes in stream flow and sediment
discharge, and thus minor alternation in long profile gradients may occur. Within a
shorter time, a steady state may be found to exist, in which erosion, transport and
deposition get exactly balanced. The landscape would be slowly changing. But due to
self-regulating mechanisms in the process involved the drainage net work may be
regarded as being in a state of equilibrium. The present basin under study also
undergoes changes that can be explained by considering the above mechanisms of
landform development. However, here causes like sheet erosion, shifting of channels,
river bank erosion, sedimentation and finally the human interference can be adhered
to identify, evaluate and interpret the change of landform in the basin.
i.
Changes due to sheet erosion
Sheet erosion in the basin takes place when the force provided by the flow of
water exceeds the resistance of soil. Sheet erosion in the basin is associated with
laminar flow on surface which is smooth or slightly rough. Large concentration of fine
particles in channels is attributed to overland flow during flood storms. Emmett
,1970[10] demonstrated that overland flow is distinctly laminar. Sheet erosion is a
complex process of land denudation as it is affected by a large number of interrelated
variables.
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Soil erosion comprises soil creep and sheet wash phenomena. Soil cre ep occurs
on convex divides and interfluves area, and the sheet wash goes on slopes, attaining
maximum intensity on the steepest slope segments. Sheet erosion involves two
dynamic processes: (1) the action of rain beat on weathered rock or soil, and (2) th e
transport of sediment by the flowing water.
The variation and distribution of sheet erosion are directly related to the
rainfall distribution and its variability and co -efficient of rainfall variation in the
Mutanga-Nona basin and its adjacent areas. Sheet erosion in the basin is very high
where there lie the foot-hills of Bhutan Himalaya. Here slope ranges at more than 10 o .
The rate of erosion in this part is approximately 0.15 m/year. The bhabar alluvial foot
slope has been marked by less sheet erosion. Here deposition processes due to energy
loss caused by the river flash water have become dominant. On the other hand, the
middle built-up land has been under sheet erosion at the rate of 0.05 m/year. The
lower reach of the region comprising active flood plain of the basin has eroded the
land surface at the rate of 0.03 m/year. Here peripheries of marshes, swamps, beels
and other depressed pockets have been under constant sheet wash. Because of this
phenomenon, sedimentation has been a regular phenomenon o n the beels of these
depressed areas. Thus most of the low-lying areas of the basin have gone up and now
the areas have converted into rich agricultural field. Only the deepest portions of
these low lying areas have remained with a bit unchanged condition.
ii.
Changes due to shifting of channels
The shifting of channels has caused the change of landform characteristics.
Here, the resultant landform developed due to channel shifting is discussed in brief.
The channel shifting has changed the fluvio-dynamic situation of the basin. This has
ultimately modified the flow or discharge pattern. Channel geometry, channel
morphology and overall hydraulic situation, particularly in the lower part of the
Mutanga-Nona basin have been caused by frequent shifting of channels. The river has
been regularly suffering from overbank flow. So, there have been deposits of huge
amount of sand on the beds and banks of the channels, especially along those of the
trunk channel. In fig. 3 shifting of channels of the Mutanga -Nona basin is shown. The
river bed being continuously loaded with sediment deposits during each and every
high flood water makes itself high above the agricultural field. So, the river banks got
either breaches or slow changes to mark their shift.
iii.
Changes due to river bank erosion
The river bank erosion is one of the major elements of landform characteristics
of the Mutanga-Nona basin. Bank erosion is very active in the middle part of the river
basin, near Tamulpur, Dongpar and Pub-Hawli villages. Near the Pub Hawli village
the eastern bank is eroded by about 5-8 m every year of flood. Here, the alternate clay
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and silt formation has made bank erosion much easier. There is a continuous tendency
to have balance and make adjustment upon channel flow dynamics included in the
geomorphic processes to attain an equilibrium of channel form. Bank erosion has also
increased the suspended and bed load of the river which ultimately gets sorted at the
lower reaches of the basin. The bank erosion has changed the landform character istics
of the basin particularly in the lower part of the basin.
River bank erosion near the Mejguri villages indicates that incision of river bed
has also increased suspended load to develop marginal and point bars few kilometers
down-stream from the Ulubari and Dongpar villages. Heavy bank collapse which had
caused damage of the agricultural land near Dongpar , shows the landform change in
that part of the basin.
iv.
Change due to sedimentation
Sedimentation acts as one of the major factors for change of f luvially
developed landforms. Fluvial deposits fall into two types – lateral and vertical
accretions. Lateral accretion deposits result from redistribution of coarse stream
bedload in laterally shifting channels. Fine-grained material deposits over banks
during highflood constitute accretion deposits. The channel bed deposits with sand
during flood flow period near Bilpar has indicated sedimentation processes
particularly at the lower part of the Mutanga-Nona basin. In the upper course near the
village Mejguri, the channel has some transitory channel deposits mainly of bedload
nature. This is later found as more durable channel fill or lateral accretions. Channel
fill deposits are very common in the lower part of the basin which is marked by
abandoned channel segments. Marginal and point bar deposits have been distinct few
kilometers down-stream from Kawli river meet point with the Mutanga -Nona. Below
the point the Gayaldong joining with Mutanga-Nona a number of large point bars has
developed near Dongpar, Pakribari, Nakhuti and Ulubari villages. Vertical accretion
deposits are observed in the Bilpar area. Here fine-grained suspended sediment
deposits due to overbank flood flow are common. Sediment deposits upon overland
floodplains form splays due to local accumulation of bed load material spread from
channels on the adjacent flood plains.
v.
Change due to human interference
Man has always been recognized as an instrument in the change or
modification of landform. He can use the river’s water, manage channels a nd make
reservoir, irrigation channel, sluice gate etc. All these have direct or indirect
influences on landform change over space and time. For instance, people engaged in
rabi crops or winter farming construct some boulder patching along the channel.
After on-setting of monsoon the flow of river is changed and the diversion of channel
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may occur leading to changes of landform characteristics. This phenomenon has been
common in the upper reach of the river Mutanga-Nona.
VI. Conclusion:
Even as the Mutanga-Nona river is a creek (tributary) type, it has far -reaching
impact on drainage network, channel pattern, hydraulic dynamics and characteristic
landform assemblages. The river has been very problematic since 1950 great
earthquake causing frequently shifting of channels. The Nona (i.e. the lower reach of
the Mutanga-Nona) river is least investigated area even as the Ohio creek in the USA
is comprehensively studied by more than 17 times. The Mutanga -Nona river located in
the depressed Bramhaputra valley bounded by high hills of the Bhutan Himalaya in
the north attended by copious rains needs proper study and needful management of
topographic, hydrologic and hydraulic and land use situations for better yield and
environmental balance of the basin.
References :
[1]
Petts. E.G.1983 : ‘Rivers – Sources and Methods in Geography’ Butterworth & Co. Ltd., 1983,
Pp-141-181.
[2]
Schumm, S.A.1977: ‘River Metamorphosis’ in Gregory, K.J. (ed), River Channel Changes, John
Willey and Sons.
[3]
Gogoi,B.and Barmen, R.1991: The Burhi Dihing valley and its Adjacent Area:A study in
Historical Geomorphology, North-Eastern Geographer,vol.23 no 1 and 2 Pp.33-43.
[4]
Sharma S.K. 1989: ‘Seismicity and Seismic Risk in North-East India’ in Mahanta, P. (ed), Assam
in 2000 A.D. Prove. Workshop on Puturology Awareness held at Dibrugarah
[5]
Auden, H.B.1959: ‘Earthquakes in Relation to the Damodar Valley Projects’ Seminar Series1,Roorkee 10-12 February Pp-212-216.
[6]
Wadia, D.N.1952: ‘Geology of India’, (4th Ed) Tata McGraw Hill Publishing Co.New Dilhi, Pp403-04.
[7]
Barman,R1986: ‘Geomorphology of Kamrup District: A Morphometric and Quantitative
Analysis’ An unpublished Ph.D. Thesis, submitted to G.U.
[8]
Emmett W.W 1970: The hydraulics of overland flow U.S.Geol.Surv.Prof. Paper No. 622 A
[9]
Oldham,R.D 1899: Report on the great earthquake of 1897, Calcutta, Geological Survey of India.
[10] Talukdar, A.K 1998: Fluvio- Geomorphic characteristic of the Mutanga-Nona River Basin in
Assam, an unpublished M.Phil Dissertation, Gauhati University.
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