December 2005 Issue

AID NORTH EAST CELL NEWSLETTER

Background Information on Assam Floods
Text Box: The Brahmaputra basin represents an acutely flood-prone region characterized by awesome hazards of flood and erosion that create an annual mayhem of devastations bringing untold miseries to the people and causing colossal loss and damage to public property and infrastructure (Fig.1). The greatest single casualty due to recurrent floods is the agricultural sector which happens to be the mainstay of the economy. The extent of damage caused by the hazard has increased significantly in recent years particularly after the great Assam earthquake of 1950 which recorded 8.7 on the Richter scale. 1500 people were killed - this was among the strongest earthquakes recorded in the 20th century. The dammed tributaries of the Bramaputra River, like the Dihang, Dihing and Subansiri were breached a few days later and resulted in serious flooding. Most of the loss of life was as a result of the flooding and not directly from the earthquake. The Brahmaputra valley had experienced major floods in 1954, 1962, 1966, 1972, 1974, 1978, 1983, 1986, 1988, 1996, 1998 and 2000. 40 percent of its land surface susceptible to flood damage - the total flood-prone area in the Brahmaputra valley is 32 lakhs. The floods in Assam are caused by a combination of several natural and anthropogenic factors. Given are the following: Dynamic monsoon rainfall - the single most important cause for frequent occurrence of flood in this region is the extremely dynamic monsoon rainfall regime in the backdrop of the unique physiographic setting. The water yield of the Brahmaputra basin is among the highest in the world. This, together with the limited width of the valley and the abruptly flattened gradient, leads to tremendous drainage congestion and resultant flooding. Unique environmental settings: The Brahmaputra basin vis-à-vis the eastern Himalayas, highly potent monsoon regime, weak geological formations, accelerated rates of erosion, rapid channel aggradations, massive deforestation, intense land use pressure and high population growth especially in the floodplain belt, and ad-hoc type temporary measures of flood control are some of the dominant factors that caused and/or intensify floods in Assam. Earthquakes are pretty significant enough to bring about irreversible damages. Inundation of riverine areas: This is due to overtopping of banks by the Main River and tributaries. The problem of drainage congestion especially near the outfalls of the tributaries during high flood stages of the river. Bank erosion and channel instability: The numbers talk for themselves: The period 1953 to 1998 saw the worst of the Brahmaputra. A table of statistics is provided in the appendix *. It indicates that flood damage rose up to as high as 664 crores (Rs) in the year 1988 and 700 crores (Rs) in 1998. The 1998 flood is considered to be the most severe one since 1950. During this flood season, the Brahmaputra remained above the danger level for 42 to 99 days at 6 major gauge sites on the river. The floods came in four major waves from June to September, the fourth one occurring in September being the most severe. The synchronization of flood peaks of several major tributaries with the main stream led to further intensification of the hazard. All the 21 districts in the valley were flooded affecting a population of 47 lakhs in 5300 villages and damaging 9.7 lakhs ** hectares of cropland. Besides, 30900 houses were washed away or damaged and 156 numbers of human life and 7814 cattlehead were lost. Breaching of embankment had been a major cause of intenfication of the 1998 flood hazard which recorded as many as 139 breaches. The flood waters of the Brahmaputra had submerged the Kaziranga National Park for almost a month with 1-3 m depth of water taking a toll of 652 wild animals including 39 rhinos, 7 elephants and 23 wild buffalos. Conclusion: Growing up, I remember how we were stuck in Goalpara (a lower Assam district) – trying to navigate our vehicle through the virtually “invisible” roads by looking at the side trees. It’s a paradox – here you have pouring rain and muddy waters, the wild and ruthless river during summers while one sees “beach festivals” (a big tourist attraction!) on the Brahmaputra thanks to the dry sand beaches. I bring to an end our little walk down memory lane with a quote by an un-named seismologist. “Why are we so helpless in containing the spates of Brahmaputra and coping with its flood hazard? Why do our efforts go awry and all civil engineering measures end up in shambles? The answer, in my opinion, lies in our failure to recognize the reality of active faults and continuing crust movements in this geo-dynamically restless region. Understandably, the flood coping measures have never been designed to accord with this recognition.” Appendix *Table: Statement showing Flood Damages During 1953 to 1998, Assam ** Lakhs - 0.1 million Sources http://www.southasianfloods.org/document/ffb/ http://www.ias.ac.in/currsci/may25/articles13.htm http://asc-india.org/gq/19500815_indochina.htm

[Text Version]

The mighty Brahmaputra River at Sunset.

(Assam Govt Website)

The many forms of the River Brahmaputra River running through the valleys of the Northeast.

(Assam Govt. Website)

Flood rescue by the India army

(Tribune India Photo)

Villagers use banana trunks as a makeshift raft during a flood in Hajo in Assam

(Reuters Photo)

A man carries his son on his shoulders through floodwaters as they move to higher ground in Chanamari, 50 kms (31 miles) east of Guwahati.

(Reuters Photo)

Assam Floods

(BBC)

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Sl No.

Year

Area Affected
(million ha)

Population Affected
(million)

Total Damage
(Rs. Crore)

1

1953

0.080

0.410

2.66

2

1954

3.150

1.680

15.97

3

1955

1.410

0.800

3.71

4

1956

0.600

0.560

3.26

5

1957

0.400

0.310

4.52

6

1958

1.250

0.470

2.70

7

1959

1.040

1.760

8.39

8

1960

0.470

1.320

7.76

9

1961

0.190

0.250

0.57

10

1962

1.620

4.050

20.23

11

1963

0.580

0.830

2.06

12

1964

0.760

0.770

2.76

13

1965

0.600

0.240

0.69

14

1966

1.780

4.650

22.53

15

1967

0.260

0.680

2.44

16

1968

0.410

0.920

8.36

17

1969

0.810

1.470

8.46

18

1970

0.720

1.710

10.43

19

1971

0.360

0.670

5.63

20

1972

1.100

3.200

24.15

21

1973

2.750

2.290

16.41

22

1974

1.120

2.850

20.14

23

1975

0.010

0.030

0.34

24

1976

0.570

1.460

11.98

25

1977

1.100

4.550

31.09

26

1978

0.310

0.920

4.08

27

1979

0.670

2.350

28.14

28

1980

1.160

3.360

39.80

29

1981

0.460

1.360

7.40

30

1982

0.610

1.420

21.89

31

1983

0.730

2.260

56.18

32

1984

1.520

5.680

50.83

33

1985

0.650

2.380

54.84

34

1986

0.430

2.350

204.60

35

1987

1.530

10.490

346.60

36

1988

3.820

8.410

663.84

37

1989

0.690

2.403

0.00

38

1990

0.488

1.692

74.56

39

1991

0.997

5.307

191.15

40

1992

0.213

0.974

26.56

41

1993

1.348

5.261

0.215

42

1994

0.053

0.177

0.20

43

1998

0.972

4.698

700.00