Global Perspectives on Geography (GPG) Volume 2, 2014 www.as‐se.org/gpg The Importance of Geomorphology in Understanding Natural Hazards with Special Reference to Hazards of The Dhansiri River Basin in The Golaghat District of Assam, India Nitashree Mili*1, Shukla Acharjee2 Centre for studies in Geography, Dibrugarh University, Dibrugarh, Assam, India. 1*
[email protected]; [email protected] Received 7 August 2013; Revised 21 January 2014; Accepted 23 January 2014; Published February 2014 © 2014 American Society of Science and Engineering Abstract A hazard is a naturally occurring process or event which has the potential to cause loss of life and property. Natural hazards are threatening events, capable of producing damage to physical and social space where they take place not only at the moments of their occurrence, but on a long term basis due to their associated consequence. In present day context, the applied geomorphologic knowledge has become very important for better understanding of natural hazards. The knowledge of geomorphology helps in mitigating various hazards or to reduce the impact to a great extent. This paper focuses on the role of Geomorphology in the prevention of various natural hazards with special emphasis to flood and erosion hazards caused by the dhansiri river of Golaghat district of Assam. Keywords Hazard; Geomorphology; Flood; Erosion; Dhansiri; Assam Introduction
A hazard implies the probability of a destructive phenomenon occurring at a particular place. If the destructive phenomenon is a product of nature such as flood, landslide, earthquakes or volcanic eruption, it is a natural hazard. Study of natural hazards and their effects happen to be one of the most dynamic areas of Geomorphology. Geomorphology is a branch of physical Geography which studies the origin and development of different types of landforms on the earth’s surface and the processes modifying those landforms. Natural hazards are considered within a geological and hydro meteorological conception. These hazards are strongly related to geomorphology since they are important ingredients of the earth’s surface dynamic. Hazards are results of sudden changes in long term behaviour caused by minute changes in initial conditions (Scheidegger,1994). Geomorphology has contributed enormously to the understanding and assessment of different natural hazards. Geomorphological work includes not only the understanding but the mapping and modelling of Earth's surface processes. Geomorphologists are becoming increasingly involved in the prevention of hazards, through vulnerability analysis, hazard and risk assessment and management. The work of geomorphologists is therefore of prime importance for disaster prevention. Human activities have had a huge impact on the environment and landscape, through industrialisation and land‐use change, leading to climate change, deforestation, desertification, landdegradation, air and water pollution. These impacts are strongly linked to the occurrence of geomorphological hazards, such as floods, landslides, floods, soil erosion, and others (Ayala & Goudie, 2010) which are strongly related to geomorphology since they are important ingredients of the Earth's surface dynamics. The present paper is a attempt to study the role of geomorphology in understanding the natural hazrds . Objectives

To highlight the concept of natural hazards. 
To study the major natural hazards of the study area. 1 www.as‐se.org/gpg Global Perspectives on Geography (GPG) Volume 2, 2014 
To find out the relationship between Geomorphic study and natural hazard management: Methodology
The required informations are collected from both primary and secondary data sources. Primary data and information are collected through field survey and participant observation. Secondary data are collected from various relevant books, journals etc. The required survey of India toposheets (Scale 1:50,000) of 1974 were scanned, georeferenced, mosaiced and used as resource maps. IRS‐P6 LISS‐III, digital image of 2000 and 2011 on 1:50,000 scale obtained from National Remote Sensing Centre (NRSC), Hyderabad, were used to map the geomorphological attributes during 2008 and 2011. The digital image was registered to the base map using a set of Ground Control Points (GCPs) and preprocessed in the ERDAS IMAGINE software environment. Map to image georectification process was adopted for geometrical correction of satellite images. ‘UTM’ projection was used with spheroid and datum as ‘WGS84’. Ground control points were obtained from Survey of India 1:50,000 toposheet. The geomorphological attributes of 2000 and 2011 were prepared by digitizing in Arc GIS and incorporated in a GIS domain for change analysis. ASTER image was used to prepare the slope map of the study area. Study Area
The area under study is located in the south bank of the river Brahmaputra in Assam. Among the 27 district of Assam, Golaghat district has been selected as a sample district to understand the problems of natural hazards. Geographically in the Golaghat district, Dhansiri basin considered as one of the important geographical unit with respect to agro economy and human settlement, is the main river of Golaghat district, Assam. The Dhansiri river, one of the major south bank tributaries of Brahmaputra has long been considered as a problematic river in the history of Assam due to recurrent and extensive flooding and bank erosion. As flooding and erosion continues to affect major portion of the growing population in the Dhansiri basin, people suffering from persistent flood and erosion problems are seeking methods to mitigate flood and erosion damages. IN D I A
FIG. I MAP OF THE STUDY AREA Natural Hazards
The term natural hazard implies the occurrence of a natural condition or phenomenon, which threatens or acts hazardously in a defined space and time. Different conceptualizations of natural hazards have not only evolved in time, they also reflect the approach of the different disciplines involved in their study. In this sense, a natural hazard has been expressed as the elements in the physical environment harmful to man (Burton and Kates, 1964); an interaction of people and nature (White, 1973); the probability of occurrence of a potentially damaging phenomenon (UNDRO, 1982); and as a physical event which makes an impact on human beings and their environment (Alexander, 1993). A natural hazard is a threat of a naturally occurring event that has the potential negative effect on people or the environment. Natural hazards are always potentially disastrous, the extent of damage depends on frequency and magnitude of the event. Those natural hazards that cause losses of human life and great material damage to economics are called Disaster and Catastrophes. 2 Global Perspectives on Geography (GPG) Volume 2, 2014 www.as‐se.org/gpg Relationship between Geomorphologic Study and Hazard Management
One of the major problems in hazard control and management has been the lack of scientific understanding of the complex physical processes involed in the occurance of hazards. Hazards cannot be prevented from occurring but their impacts can be reduced through proper management system. Flood and erosion control and management are necessary not only because they impose a curse on the society but the optimal exploitation of the land and proper management and control of water resources are of vital importance for bringing prosperity in the region. But this cannot be technically feasible without proper understanding the relationship among the factors affecting river flow, sediment load, channel pattern, channel migration etc. and their resultant impacts on man. Geomorphologic knowledge helps for better understanding the effects of the hazards, their frequency and magnitude. Primarily the interest of a geomorphologist concerns regarding flood and bank erosion are the following: 
Concept of Flood and Flood plain, floodplain delineation, flood deposit recognition. 
Monitoring of changes in river channel position and pattern. 
Determination of the probability of flooding from a river. 
The effects of such flooding 
The extent of flooding. 
Flood hazard management measures. 
Channel Pattern. 
River flow pattern. 
Grain size analysis of bank materials. All these information can be used to determine the areas prone to flood and bank erosion. Mapping of flood prone zone is a primary step involed in reducing the risk of the region. The information can also be used to control the landuse in the floodplain areas. Today, the increasing pressure of population on floodplain for agriculture and settlement and intensification of hazards due to flood and erosion, the engineers, hydrologists, fluvial hydrologists and planners need to know as accurately as possible the probable flood magnitudes and their occurrence for implementing various water resources development plans. Flood frequency analysis is thus extremely useful in risk analysis and economic development and planning of flood prone areas by means of providing the probability of occurrence of the future flood events. Similarly the knowledge of channel pattern, river flow and bank materials help in adopting various structural measures. The geomorphic ideas help to a great extent in the implementation of hazard mitigation policies. Now‐a‐days Geographical data and information relating to Remote sensing and Geographical Information System(GIS) have become essential for better understanding of the natural hazards. The remote sensing technology helps in providing accurate information about the spatial and temporal extent of flood by way of delineating the flood inundated areas along the river course. With the availability of repetitive remote sensing data, it is quite possible to monitor the variations in extents of flood inundation. River sediments and related problems like erosion and deposition are also studied through remote sensing. Erosion‐prone areas as well as the area of intensive bank erosion can be detected through remote sensing and their extents, dimensions, patterns and process can be analysed leading to formulation of effective erosion control plans. Hazards in the Dhansiri River Basin in Golaghat District Of Assam Flood
From the geomorphic point of view Dhansiri river is characterised by meandering pattern, Channel shifting, high flow velocity during monsoon period and prone to various fluvio‐geomorphic hazards. The two most common hazards of Dhansiri River Basin in Golaghat District are Flood and Bank Erosion. Defining a flood is a difficult task, partly because floods are complex phenomenon and partly because they are viewed differently by different people. A more general definition of Flood is given as “A flood is a body of water which rises to overflow land which is not generally submerged”. Assam is a land of rivers. Rivers present a potential threat to human populations and property through flood, drought and erosion. They therefore have potential social and economic as well as physical relevance. Flood is probably the most recurring, wide spread, disastrous and frequent natural hazard of Assam. It is a matter of concern that every year Assam suffers extensively due to floods and river banks erosion. Flood may be considered as the biggest cause of loss of life and property in Assam. The two main river systems i.e. the Brahmaputra and Barak have invariably been inundating the plains of Assam in different time. The flood statistics of Assam shows that the major earthquakes of 1897 and 1950 have caused abrupt changes in the fluvial regime of Assam. 3 ww
ww.as‐se.org/gp
pg Global Persp
pectives on Geeography (GPG
G) Volume 2, 22014 Th
he Dhansiri b
basin in Golaaghat is highlly vulnerablee to flood maanagement sttrategies. Dh
hansiri presen
nts challengee in terrms of long and recurrin
ng flood hazzard. Flood in i the Dhan
nsiri Basin is characterizeed by their extremely laarge maagnitude, hig
gh frequency and extensivve devastatio
on. It occurs in the middlle and lower reaches of D
Dhansiri and the pro
oblem is mo
ore pronouncced in the do
ownstream of o NH‐37 acrross Numalig
garh. Floods of extreme high h
magnitu
ude occcurred in thee sub basin in
n the years 19
954,55,59,60,770,76,86,87,8
88,89, 91, 98, 2000, 2004, 22010 and 20111. FIG. II DIS
SCHARGE HYDROGRAPH TABLE I MAGNITUDE AND
D DAMAGED CAUS
SED BY FLOOD IN THE GOLAGHAT D
DISTRICT DURING
G 2004‐12 2004‐05 2007‐08 2
2011‐12 No o
of villages 101 nos 1332 no’s 20
06 no’s No of afffected people 10259 86696 8
7
70294 Agriculturral area affected 42763hec 10
0322 hec 1 lak
kh 211 hec Crop
p damaged 4405 hec 240.95 hec 50 tho
ousand hec Sou
urce: “The flood i
in Golaghat Disttrict: causes, imp
pacts and remed
dies”‐Mandira sa
aikia.{IJCAES jou
urnal,ISSN:2231‐4
4946} Th
he major porttion of the rivver course is within the o
original state Nagaland an
nd terminatin
ng state Assam
m. In Nagalaand, thee river passess through a h
hilly course i
n the upper catchment aand causes flo
ood only in t
the foot hill a
areas of Kohiima disstrict, around
d Dimapur to
own. But the inundation s
stays only forr a day or two
o at the mostt. In its coursse in Assam a
also, no major inund
dation generaally takes plaace upto Bok
kajan. The prroblem of flooding becom
mes more com
mplicated in the Go
olaghat districct. The main
n causes of flo
ood in the sub
b‐basin are: i
i.
Heavy rainfall: Preecipitation over the basin
n is not unifform. High intensity i
of rrainfall with average ann
nual monsoo
on rainfall of f 1.158 mm. Beeing located in the monso
oonal regimee the basin reeceives heavyy rainfall durring monsoo
on season. Frrom the anaalysis of hydrrograph, it iss found that during mon
nsoon period
d (May‐Oct) the discharg
ge peaks weell coincide with w
corresponding high
her water levvel. The dailyy discharge and a
water leevel (stage) data of Dhan
nsiri river att Numaligarh
h Station havve been plottted for the yyear 1998, 199
99 and 2000 to show th
he pattern of changes in fllow characteristics (Fig. II and Table II). iii.
Steep slopes s
of the river in th
he hills: Majjor portion o
of the river iss in the steep
p hills of Nag
galand (Fig. I
III). Whenevver there is rainfall in the t
hills watter rushes do
own to the plains from extensive caatchment areeas, flooding
g the plains. iiii.
Deforestation and
d landslide p
proneness in
n the upperr catchmentt: Cleaning o
of the forested hillslopes a
and ultivation, co
onstruction o
of roads, settiing up of resiidence etc. arre very comm
mon both in the also thee plains for cu
upstream
m and downstream of thee river which
h is a major caause of flood
d. Again, the r
rocks of Nagaland being s
soft, the eartthquakes mayy easily causee landslide. L
Landslide also
o occur due t
to heavy sum
mmer rain and
d may block the course o
of the river an
nd flood occu
urs. ivv.
Highly meanderin
ng and shiftiing nature o
of the river i
in the plain:: The geomettrical pattern
n of the coursse is highly i
rregular in th
he plains whiile maintainiing almost a c
constant and
d less irregulaar course in t
the hilly terraain. bein (1966) th
he meander usually appeears whereverr the river flo
ow through f
fine Accordiing to Leopold and Langb
grained alluvium. In this partticular case the river flows f
throug
gh the unco
onsolidated alluvial terrrain predom
minantly com
mprising sand
ds and clays. Besides, thee river carry enormous qu
uantities of sediments frrom 4 Glo
obal Perspectivves on Geograp
phy (GPG) Vo
olume 2, 2014 w
www.as‐se.org/gpg the hillss and on reaaching the pllain, sedimen
nts are depossited on the channel bed
d (Fig. IV). Th
he channels are thus fillled up and th
he water dig o
out different courses. FIG. IIII SLOPE MAP O
OF THE DHANSIRI RIVER BASIIN SHOWING T
THE UPPER COU
URSE FALLING UNDER STEEP
P SLOPE FIG
G. IV IRS P6 IMA
AGE OF A PART
T OF DHANSIR
RI RIVER.SHOW
WING HIGHLY M
MEANDERING C
COURSE AND T
THE CUT OFF FORMING OXBO
OW LAKES Ba
ank Erosio
on
Th
he Dhansiri sub basin fallls in highly s
seismic zone and experieences several earthquakess in a year allong with heeavy dow
wnpour in the t
hilly catchments. Th
his factor co
oupled with heavy deforeestation in tthe hill catchment leadss to con
nsiderable so
oil erosion on
n the steep sllopes of the h
hills.The erod
ded soil is then transported by the rivver. On reach
hing thee plain the trransported m
materials get d
deposited at the river bed
d due to sudd
den change o
of the river grrade from a v
very steeep slope to g
gentle slope l
leading to meeander which
h ultimately results in ban
nk erosion. E
Erosional pro
ocesses are m
more acttive during monsoon m
and
d when the water level recedes the bank level. During the receding staage of the rivver, diffferent types of shear faiilure also took place and
d were obseerved around
d Kamargaon
n, Golaghat areas a
along the Dh
hansiri River channel (Du
utta, 2007). As A water levvel receded in
n the channeel, saturated levee materrial lost supp
port fro
om the chann
nel side. Thesse resulted in
n shearing of blocks from the saturated
d bank due to
o its own weiight. 5 ww
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pg Global Persp
pectives on Geeography (GPG
G) Volume 2, 22014 F
FIG. V A SUBSET
T OF LOWER PA
ART OF DHANSIRI RIVER SHO
OWING BANKL
LINE SHIFT AND
D BANK EROSIO
ON (E=EROSIO
ON) IN BETWEE
EN THE YEAR 2000 AND
D 2011 TA
ABLE II MAJOR EA
ARTHQUAKES IN T
THE NORTHEASTERN REG
GION IN RECENT P
PAST Place
e Cachar Shillon
ng plateau
u Sibsagaar Myanm
mar Year March 2
21, 1869 Magnitud
de June 12, 1
897 8.7 About 1542 p
people died 7.0 Property damage 7.5 Property damage August 31, 1906 Decembeer 12, 1908 7.8 Rema
arks Numerous eaarth fissures and sand craters 2
Srimang
gal July 8, 19
918 7.6 4500 km areea suffered damaage SW Assaam Septembeer 9, 1923 7.1 Property damage Dhubrri July 2, 19
930 7.1 Railway linees, culverts and bridgess cracked 7.6 Destruction o
of property 7.0 Destruction o
of property 7.2 Destruction o
of property 7.5 7.6 Destruction o
of property Severe d
damage About 1520 p
people died. One of thee largest known quaake in the histo
ory January 27, 1931 Nagalan
nd 1932 October 23, N‐E Assaam 1943 Arunach
hal July 7, 19
947 Upper Assam July 29, 19
949 Assam
m Upper Assam Patkai Range, Arunach
hal Manipu
ur‐
Burma bo
order Darjeeling Indo‐Myan
nmar borderr August 15, 1950 8.7 1950 7.0 Property damage 1954 7.4 Property damage 1959 August 6, 1988 7.5 Property damage 7.5 No casualtyy reported Sou
urce: “STATUS OF SEISMICITY
Y IN THE NOR
RTHEAST INDIIA AND EARTH
HQUAKE DISA
ASTER MITIGAT
TION”‐ R.P.Tiw
wari, Departmen
nt of Geo
ology, Pachhung
ga University Co
ollege, Mizoram University. 6 Global Perspectives on Geography (GPG) Volume 2, 2014 www.as‐se.org/gpg TABLE III DETAIL AFFECT OF EROSION CAUSED BY RIVER DHANSIRI IN GOLAGHAT REVENUE CIRCLE AREA SINCE THE YEAR 2001 Year 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 Total Total Damage A 14 44 95 115 53 07 Nil 08 31 43 08 418 bigha B Nil 10 16 33 16 Nil Nil Nil Nil 02 03 80 nos Area Eroded (A)* {area in bigha} Families become homeless(B)* Source: Revenue circle Office, Golaghat. Bank erosion, channel shifting and damage of human habitats as well as agricultural land etc. have been common phenomenon of the river Dhansiri. The Dhansiri river basin is one of the most erodible basins in India. The earthquake in 1950 may be said to be a threshold point after which the bank erosion problem has become more severe and intensive throughout the Brahmaputra valley of Assam (Table II). The Dhansiri had alone eroded away over 418 bighas of land between 2002 and 2011 (Fig. V). Loss of vast fertile land has made nearly 100 families homeless and landless particularly in the last 10 years (Table III). Flooding during the monsoon period due to heavy rainfall and fast flow velocity are also the causes of bank erosion. Being located in the monsoonal regime, the Dhansiri basin receives heavy rainfall during the monsoon season. Dhansiri gets floods from May to September. Over 80% of the flow and over 95% of the sediment contribution take place during this period. Due to meandering nature of channel pattern and excessive sediment discharge, there is constant shifting of the channel. The process of constant shifting due to bank erosion of the river has been continuing through ages. Mitigation Strategies Taken up So Far

Construction of embankment along both side of the Dhansiri for flood mitigation. The total length of embankment constructed in Dhansiri sub basin is only 23.05 km. 
A number of anti erosion schemes have been taken up by the Government from time to time to provide protection in the erosion affected reaches. Altogether 9612 hac of land including Golaghat township have been protected by various anti‐erosion measures. Conclusion
Hazards are a key interaction between humans and physical environment. It is a complex Geo‐ Environmental phenomenon; therefore, it needs a integrated approach composed of Geomorphological, Hydrological, Meterological and Anthropogenic aspects to lessen the disastrous effects of Natural hazards. Geomorphologic knowledge can contribute to the choice and design of various strategies for hazard management. The dynamism of the Earth's surface is enclosed within a temporal and spatial scale. The response of the landform to the changes caused by the processes corresponds to the magnitude and frequency of the events, the resistance of the involved materials and the size of the concerned landform (Summerfield, 1991). Natural hazards take place in a certain place and during a specific time, but their occurrence is not instantaneous. Time is always involved in the development of such phenomena. For example, the intensity and duration of rainfall in conjunction with the nature of the fluvial system, developed also on a time basis, would determine the characteristics of the flooding. The contribution of geomorphology to the field of natural disasters is mainly through the elaboration of hazard assessments. In general, such assessments comprise stages like mapping, modelling, prediction and management proposals, using field observations, photogrammetry, geographical information systems and remote sensing, the zonation and mapping of different hazards is done. Modelling approaches consider not only the understanding of present, but past events, leading to accurate predictions of the consequences a geomorphic hazard may have on a determined landscape under a given conditions. Thus, geomorphological work includes not only the understanding but also the mapping and modelling of Earth's surface processes, many of which directly 7 www.as‐se.org/gpg Global Perspectives on Geography (GPG) Volume 2, 2014 affect human societies. In addition, geomorphologists are becoming increasingly involved with the dimensions of societal problem solving, through vulnerability analysis, hazard and risk. Dhansiri, has been experiencing a continuous process of migration by way of bank erosion during flood periods. The severity of floods has further amplified under the influence of human intervention. If this recurrent phenomenon is not mitigated, it would be difficult to achieve the economic development. ACKNOWLEDGMENT
The authors are thankful to Dr. Munindra Konwar for his constructive suggestion during the preparation of the manuscript. REFERENCES
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Dutta, M.K., 2007. Dhansiri River Channel, Assam – A geomorphologic attribute, Unpubld. Ph.D. Thesis, Dibrugarh University, Assam. [5]
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White, G.F., 1973. Natural hazards research. In: Chorley, R.J. (Ed.), Directions in Geography, Methuen, London, pp. 193– 216. Nitashree Mili was born in Dibrugarh on 19 September, 1985 and received Master degree in Fluvial Geomorphology from Gauhati University, Assam(India). Currently she is a Lecturer in the Centre for Studies in Geography, Dibrugarh University, Assam. She joined there in the year April 2010. Her research areas are mainly in the field of Fluvial geomorphology and environmental science. She participated, presented research paper in national and international level seminars and conferences and published research papers in the reputed journal. Ms. Mili, Lecturer can be reached at [email protected]. Miss Shukla Acharjee got her Ph.D. in the year 2010 and she has published a few research papers in refered journals. 8