Floods, Erosion and Ecological Impact in Assam
Floods and riverbank erosion are the most serious recurring natural problems of Assam and have a deep impact on its economy, ecology and society. Every year the Brahmaputra and its tributaries swell during the monsoon, submerging farmland, villages, roads and even wildlife habitats. Along with flooding, the shifting and erosion of riverbanks permanently consumes land and shrinks islands such as Majuli. This chapter explains the causes and extent of floods, the erosion problem, the ecological consequences for wetlands and national parks, and the institutions and measures used for disaster management, all of which are frequently asked in ADRE, APSC and similar examinations.
Causes and extent of floods
The Brahmaputra and its numerous tributaries are the main cause of annual floods in Assam. About 40 per cent of the state's area is flood-prone. Floods occur mainly during the monsoon season from June to September, especially in July and August. The Barak river floods the Barak valley in southern Assam, in the Cachar region. The Brahmaputra, known as the Tsangpo or Yarlung Tsangpo in Tibet and as the Jamuna in Bangladesh, carries one of the highest sediment loads of any river in the world. Heavy rainfall in the hills, steep slopes, deforestation, the high sediment load and shifting river courses all worsen flooding. Human-induced factors such as deforestation and encroachment on wetlands and riverbeds further increase the risk, and climate change is likely to make floods more frequent and more intense.
Riverbank erosion
Erosion by the Brahmaputra is a slow but severe disaster that permanently destroys land and displaces families. Majuli, the largest river island in the world, has lost a large part of its area over the decades to bank cutting and is still shrinking. Chars are sandbars or silt islands that form in the river and are inhabited by people who are especially vulnerable to floods and erosion. Common anti-erosion measures include concrete spurs with boulders, geo-bags and bio-engineering methods such as planting vetiver grass. The Brahmaputra Board, constituted in 1980 with its headquarters at Guwahati, prepares the master plan for the Brahmaputra basin, while systematic construction of embankments began after the devastating floods of 1954, which followed the great earthquake of 1950.
Ecological impact
Floods and erosion have a major ecological impact. In Kaziranga National Park, which lies on the southern bank of the Brahmaputra, flooding submerges the grasslands and forces animals such as rhinos to migrate to higher ground, and many die in the process. During Kaziranga floods, the highway NH-27 (formerly NH-37) turns into a death trap for animals fleeing the water as they are often hit by vehicles. Wetlands such as Deepor Beel, the only Ramsar site in Assam, declared in 2002, perform vital functions including flood regulation, groundwater recharge, biodiversity support and livelihoods. Floods also damage agriculture severely, destroying standing crops every year and deepening rural poverty.
Disaster management institutions
Assam has a well-defined disaster management structure. The Assam State Disaster Management Authority (ASDMA) was established under the Disaster Management Act, 2005, and District Disaster Management Authorities (DDMA) manage response at the district level. The State Disaster Response Force (SDRF), Assam, is the state-level response force. The National Disaster Response Force (NDRF) was established in 2006, and its 1st Battalion is located at Patgaon in Guwahati. During major floods, rescue and relief operations are carried out by the NDRF along with the SDRF, the Army and central paramilitary forces. In extreme flood years, over one crore people have been affected in Assam.
Key facts at a glance
- Main flood cause: Brahmaputra and its tributaries; about 40% of Assam is flood-prone.
- Flood season: monsoon (June to September), especially July and August.
- Barak river floods the Barak valley (Cachar region).
- Brahmaputra names: Tsangpo/Yarlung Tsangpo in Tibet, Jamuna in Bangladesh.
- Embankment construction began after the 1954 floods (following the 1950 earthquake).
- Brahmaputra Board - constituted 1980, HQ Guwahati; prepares the basin master plan.
- Majuli - shrinking due to river erosion; chars are inhabited silt islands.
- Anti-erosion measures: concrete spurs with boulders, geo-bags, vetiver grass.
- Deepor Beel - only Ramsar site in Assam, declared 2002.
- ASDMA under the Disaster Management Act, 2005; NDRF (2006) 1st Battalion at Patgaon, Guwahati.
Quick revision points
- About 40 per cent of Assam is flood-prone; monsoon floods peak in July-August.
- The Brahmaputra Board (1980) plans flood control for the Brahmaputra valley.
- Majuli is shrinking because of erosion; chars are inhabited sandbars.
- Deepor Beel is Assam's only Ramsar site (2002).
- ASDMA (2005 Act), SDRF, NDRF (2006, 1st Battalion at Patgaon) handle disasters.
How to prepare this topic
- Learn the causes of floods and the share of flood-prone area.
- Note the river names and their different names in Tibet and Bangladesh.
- Link institutions with their years and headquarters.
- Remember the ecological effects on Kaziranga, Majuli and Deepor Beel.
- List the anti-erosion and disaster response measures.
Common exam traps
- Embankments began after the 1954 floods, which followed the 1950 earthquake - do not mix the years.
- The Brahmaputra Board was constituted in 1980, not immediately after 1950.
- Deepor Beel is the only Ramsar site in Assam; Majuli is a river island, not a Ramsar site.
- ASDMA is under the 2005 Act, while the NDRF was established in 2006.
- The Brahmaputra is called Tsangpo in Tibet and Jamuna in Bangladesh.
Frequently Asked Questions
What causes the annual floods in Assam and how much area is flood-prone?
The Brahmaputra and its numerous tributaries are the main cause of annual floods in Assam. About 40 per cent of the state's area is flood-prone, and floods occur mainly during the monsoon season from June to September, especially in July and August. The Barak river floods the Barak valley in southern Assam.
Why is Majuli shrinking and what are chars?
Majuli, the largest river island in the world, is shrinking mainly because of river erosion and bank cutting by the Brahmaputra; it has lost a large part of its area over the decades. Chars are sandbars or silt islands that form in the river and are inhabited by people who are especially vulnerable to floods and erosion.
Which is the only Ramsar site in Assam and when was it declared?
Deepor Beel, a wetland near Guwahati, is the only Ramsar site in Assam and was declared in 2002. Wetlands perform vital functions such as flood regulation, groundwater recharge, biodiversity support and livelihoods, and are important for flood control.
Which institutions manage disasters and flood control in Assam?
The Assam State Disaster Management Authority (ASDMA) was established under the Disaster Management Act, 2005, and District Disaster Management Authorities manage district-level response. The State Disaster Response Force (SDRF) Assam and the National Disaster Response Force (NDRF, established 2006, with its 1st Battalion at Patgaon in Guwahati) carry out rescue operations. The Brahmaputra Board, constituted in 1980 with headquarters at Guwahati, prepares the master plan for the Brahmaputra basin.
What is the ecological impact of floods on Kaziranga?
During floods in Kaziranga National Park, which lies on the southern bank of the Brahmaputra, the grasslands are submerged and animals such as rhinos are forced to migrate to higher ground, and many die in the process. The highway NH-27 (formerly NH-37) turns into a death trap for animals fleeing the water as they are often hit by vehicles.