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| Last Updated:: 13/01/2016



(Photograph: Internet)




A Hazard is a situation which poses a level of threat to life, health, property or environment. Most hazards are dormant or potential, with only a theoretical risk of harm, however, once a hazard becomes 'active', it can create an emergency situation.

The unique geo-climatic conditions of the regions make Assam and the entire northeastern region of India very prone to natural disasters like flood, earthquake and landslide. The state of Assam experiences perennial floods, river bank erosion, landslide and other environmental catastrophes. Disasters cause sudden disruption to the normal life of a society along with enormous damage to property associated with high casualty of human life. A review of the past disasters indicates that the state had to bear the devastations of two natural disaster floods and earthquake.


Natural Hazards:

·            Earthquake

·            Flood

·            Landslides


(Photographs: Internet)


Earthquakes in India are caused by the collision of the Indian Plate with the Eurasian Plate in the north. Every year the Indian Plate moves roughly 5 centimeters northward, pushing under the Eurasian Plate and forming the Himalayas and other great mountain chains in the northern part of the Indian peninsula. For great earthquakes the movement can be several meters and can covers several hundreds of square kilometers of the contact surface between the two plates. Most earthquakes in the northern part of the Indian Sub-continent are a result of this complex process. Earthquakes which occur at the margins of plates (or plate boundaries) are known as inter-plate earthquakes and account for 95% of the global seismic activity annually.

The North-eastern region of India is an earthquake prone area. The region has experienced a large number of earthquakes of tectonic origin. The risk probabilities of earthquake are less over the entire Brahmaputra valley. The region of Northeast India is seismically very active. Two major earthquakes of magnitude 8.7 occurred in 1897 and magnitude 8.6 in 1950 causing large scale damage of lives and properties in this region. Sir Edward Gait (1933) has mentioned about the occurrence of destructive earthquakes in this region in 1548, 1596, 1607, 1642, 1663, 1696-1714, 1869, 1882, and in 1897. In the present century, destructive earthquakes occurred in 1918, 1923, 1930, 1932, 1938, 1943, 1947, 1950 and in 1988.

Much of Assam lies in the Brahmaputra River Valley, except for a few southern districts. The northern and eastern parts of this valley are bounded by the Himalayan Frontal Thrust (HFF). In the eastern parts along with the HFF, there is the Lohit and Naga Thrusts. Among the large earthquakes in this region were the events in 1869 and 1897. The 1897 earthquake is well known for the dramatic accounts of violent upthrow during the shock.




(Photograph Internet)

Flood the most frequent natural calamities faced by India. A relatively high flow or stage in river, marked by higher than the usual, causing inundation of low land or a body of water rising, swelling and over flowing land not usually covered by water is termed as flood. It is essentially a natural hydrologic phenomenon with a large volume of surplus water that inundates the flood plains, interfere greatly socio - economic condition. Studies shows that flood levels to the extent of 2 meters could be brought down and severity of floods could be substantially reduced in the rivers along with generation of hydropower of the order of 30,000 MW in N.E Region.

The mean annual rainfall in the Brahmaputra basin is around 2300 mm. Internationally the Brahmaputra rank 10th in the world in terms of discharge. The water resources of NE Region has been assessed to be about 31 % of the country. However harnessing of water for irrigation and other beneficial purposes in Brahmaputra is 3%. Monsoon rainfall accounts for 75% to 80% of the annual rainfall. The flood problem has needlessly been continuing since time immemorial. This could have been overcome by the best utilization of huge water resources of the region for poverty alleviation and sustainable development which appear as disastrous flood in some part or other part of the region every year resulting in colossal damage.

Major river systems

(Photograph: Internet)

The Brahmaputra is one of the largest rivers in the world. Another important river system of Assam is the Barak, the head stream of the Meghna, rises in the hills of Manipur in India and flows south-west for 250 Km. At Lakhipur, it emerges from hills and at Bhanga, it splits into the Surma and Kushiyara which cross into Bangladesh near Karimganj. Northern tributaries of the Brahmaputra and Barak are braided and unstable in their reach. The instability of the river is mainly attributed to high sediment charge, steep slopes and transverse gradient. Apart from these the entire area is in highly seismic zone and receives Earthquake shocks of severe intensity periodically. This is also one of the factors for unstable character of the river. The Earthquake that occurred in those periods considerably disturbed the drainage network of Assam in 1897 and 1950.

The Brahmaputra and Barak river system is subjected to frequent heavy floods, drainage congestion and bank erosion resulting in extensive submergence of land, loss of life and property as well as disruption in communication system. At times the period of floods above danger level is 40 to 70 days. The impact of floods was not felt to the same extent in the past as is felt now. This is due to rapid increase of population and subsequent increase in the all-round activities of man. The flood plain is gradually occupied to meet ever increasing requirements of food and fiber and consequently the flood problem has been accentuated.


Causes of flood


Floods in the region occur due to variety of causes such as:

·           River channel carrying flows in excess of the transporting capacity within their banks. This is due to excessive precipitation that occurs in NE-India.Backwater in tributaries at their outfalls into the main river because of non-synchronization of peak floods in them.

·            Heavy rainfall in short space of time.

·            Storm

·            Aggravation of river bed.

·            Inadequate waterways at rail and road crossing and encroachment in the flood plains.

·           Degradation of catchment area in forms of deforestation, jhuming and loss of soil mantle in Himalayan friable watershed.

·            Lack of proper control of land use


The rainfall induces drainage problem occurs in naturally low land is severe and acute in this part of the country. The drainage congestion is caused due to heavy precipitation of short duration and higher flood level in the main river, which doesn't allow the water to drain into main river quickly. Drainage congestion is also caused due to construction of road, rail and embankments, which obstructs natural flow and encroachment in the riverine areas due to population pressure. The lack of sufficient capacity of drainage channel and natural bowel shape topography of land resulting from defunct river courses also contribute to drainage congestion problem.


Bank erosion of the Brahmaputra and its tributaries has become a matter of serious concern to both people and the Govt. consuming large annual exchequer of the Govt. in erosion control works. Along the valley specially in Dhemaji, Lakhimpur, Morigaon and Dhubri long reaches of river bank are eroded and consequently number of villages on record are seen left inside the Brahmaputra. The causes of heavy erosion are attributed to excessive sediment load, steep bed gradient, transverse bed slope, non cohesive erodible nature of bank material, formation of char island and consequent development of side channel. Majuli island and the Kaziranga National Park are also the worst victim of this erosion process. It is also observed below the confluence of major tributaries.


The extent and magnitude of flood problem is assessed in terms of different types of damages caused by flood. The floods of 1988 and 1998 of the Brahmaputra basin were unprecedented which completely shattered the economy of the state. Comprehensive studies have been undertaken to go into the various aspects of floods and flood control. Various aspects both structural and non-structural measures that are considered for formulation and implementation (M.U.Ghani).


Problems due to flood


The main problems due to floods are inundation, drainage congestion and bank erosion and consequence is damage to property. The problems depend on river system, topography of the place and flow phenomenon. 

The space borne satellite Remote Sensing technology is found to be an effective tool to disseminate the proper information in near real time basis.



The issues related to floods in the Brahmaputra are:

·            Narrow size valley (80-90 Km)

·            Highest rainfall (average nearly 2600 mm)

·            Tributaries are within the close range

·            Peak rainfall profile ranging from mid-May to mid-September

·            Settlement in vulnerable areas

 Source: For preparation of Environmental Atlas of Assam, ASTEC






(Photographs: Internet)

Landslide, the sudden and rapid downhill movement of soil along the hill slope is another dimension of slope instability. It now becomes a common environmental hazard all over the world. The rate of landslide is increasing day by day. Landslide being a natural hazard occurs either due to increase of load on its head or decrease of support in its toe. The nature of slope and the geomorphic processes induce landslides, but it became more hazardous as soon as the settlement process started on the hills. The landslide in the recent years was primarily man induced, the slopes of the hills of Guwahati in Assam are naturally prone to landslides for its structural peculiarities and prevailing climate of the region. The hills of the Guwahati city is coated with a thick layer of immature soil with low permeability which naturally became more landslide prone during rainy season. Growth of population and construction of houses on the steep slope zones and innumerable roads and footpaths caused removal of support at the toe of steeper part further deteriorate the situation.


The frequency of landslides increases with the increase of settlement. Unauthorized rapid growth of settlement on the hills is said to be the root cause of most of the landslides.


Man-Made Hazards:


(Photograph: Internet)


Causes of Deforestation


Forests in Assam are dwindling and the main reasons attributed to the gradual depletion of forests in Assam are:


·      The hills and plateau of the two districts Karbi Along and N.C. Hills are populated by hill tribes having their own cultural life style intertwined with forests, wildlife and jhum (Shifting) cultivation. This particular process involves 'slash' and 'burn' of forest area and natural vegetation. Original jhum cultivation had a long jhum cycle of about 20-25 years, which was allowed to elapse before the same plot of land was cultivated. In this process, the forest cover remained intact. But the increase in population demanded more cultivable land, thus shortening the period to about 4-5 years. This greatly effected the vegetation of the area, as well as the total environment.A study using satellite mapping of forest degradation due to shifting cultivation in the hill districts of N. C. hills and Karbi Anglong district, carried out at the Assam Remote Sensing Application Centre, shows that out of 423885 hectares of land under Jhum cultivation in Karbi Anglong district, 6844 hectares, became degraded forest land. Similarly out of 292309 hectares in N.C. hills, 7938 hectares are degraded. The study further shows that indiscriminate felling of tries primarily for shifting cultivation in these two districts is causing certain serious environmental problems like loss of soil fertility, soil erosion, floods and siltation in the plains.

·           Open rearing of domestic animals also contributes towards damage of the environment.

·         Particularly in Karbi-Along district, from where the bamboo, required as the raw materials for the Nagaon Paper Mill at Jagiroad, is procured. As a result it loses its capacity for growth and a large areas in Karbi Anglong have undergone the evil process of deforestation.

·           In other parts of Assam also, setting up of saw mills, veneer mills and plywood factories has caused rapid depletion of large forest areas, particularly during the last three decades. The data from National Remote Sensing Agency shows that within a period, of seven years (1975-82) about 64 million hectares of forest areas were depleted in the entire north east region.

·           The growth of tea industry has caused depletion of a large forest area. The present spate of growth of small tea gardens, many forest covers have to give way to tea plantation, thus causing further shrinkage in the total forest area.

·         Forests and grasslands have had to be shrunk by the expansion on settled agricultural practice.

·           The link between human poverty and environmental degradation is also one of the important factor behind deforestation. Lack of alternative livelihood for some and greed on the part of unscrupulous traders has led to gradual denudation of the forest resources.

·           Another poverty environment link is seen in the destruction of forest for collection of firewood. The demand for firewood being high, its supply is going on through illegal route. Even large trees are cut deep inside the forest, split into small pieces and supplied as firewood.

·           Population pressure has led to encroachment of the forestland. Since the coming of the immigrants and their settlement in the forests, the process of capturing vote banks has been going on and the result is the gradual destruction of the forest land.

·           Forest land becomes the first choice for rehabilitation of people affected by various natural calamities - thereby adds to further reduction.

·           Use of the forest as a major revenue earner has also contributed much to the depletion of forests.

·           Much destruction of forest occurs also due to building of roads, opening up new industrial towns, construction of communication towers and electrical lines.

·           In illegally procuring coal from Karbi Anglong district, much forest is destroyed.

·           For obtaining limestone from Karbi Anglong district for use in the cement factory at Bokajan, often large tracts of forests are destroyed in blasting. Another privately owned cement factory, due to start operation soon, is going to add to the depletion of forest.

·           Further, the reserved forests along Assam's border with Nagaland, Meghalaya and Arunachal Pradesh were the worst victims of encroachment and about 12% of reserved forests are under border encroachment. This takes place because, with the developmental activities in the plains people who used to live in hilly areas came down to set up habitation .in the reserved forests in these areas to enjoy the benefits of development.



Effects of deforestation on Environment


·       The shrinkage of forest cover has effected the climate of Assam adversely. The rainfall has become erratic, the temperatures have risen and in many places, the sign of desertification has set in.

·      Because of the loss of water retention capacity of the soil, rain in the upper reaches of the rivers have led to heavy soil erosion, leading to siltation of the river beds thereby causing flash floods. Such floods destroy more forest, creating a vicious cycle, and destroying a large number of varieties of precious flora and fauna, including medicinal plants.

·      The consequent floods carry any fertile top soil to fertilise the flooded land, by depositing only sand and silt destroy the quality of the soil.

·         The River Kakodonga passing through the Doyang Reserve Forest began to play havoc on the rice cultivation in the Ghilahdari Mouza in Golaghat district. The flood was caused due to heavy deforestation of the Doyang forests. In 1984-85, in a bid to stop flooding, water hyacinth was spread along the river. As a result within a few years the water-flow was greatly reduced. The net result is severe drought, affecting as many as nearby 7000 bighas of paddy field.

·      There have been widespread reports of herds of wild elephants coming inside human habitation in search of food, and damaging paddy fields and properties, trampling huts and even killing people. Lack of food in their natural habitat must have driven the pachyderms to human locality. Unless the depletion of forest area is checked, this problem will grow in future, and ultimately it will cause extinction of this great wild specie


Fig: Flood Hazard Zonation Map





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For More Information: 

Assam Disaster Management Authority


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