Floods In India, Causes, Flood Prone Areas, Consequences

Table of Contents

Context: Andhra Pradesh and Telangana experienced heavy rainfall which led to severe flooding and widespread waterlogging across both states.

What is Flood?

A flood is a state of high water level along a river channel or on the coast that leads to inundation of land.
Floods are commonly associated with a stream or river. A stream floods when its discharge is greater than the capacity of its river channel.
Excess water flows over the river banks and submerges the adjacent land which is usually dry. When it happens, the channel and the flood plain together allow the passage of water.

Causes of Floods

Natural Causes

Heavy rainfall: Heavy rain in the catchment area of a river causes water to overflow its banks, which results in the flooding of nearby areas.
- Example: In July 2023, Delhi received heavy rainfall which contributed to the flooding of large parts of the city.
Snow melt: Snowmelt and glacial melt are gradual processes and usually does not cause major floods. But sometimes glaciers hold large quantities of bounded water, which may be suddenly released with the melting of ice blocks resulting into Glacial Lake Outburst Floods (GLOFs).
- In October 2023, flash floods in Sikkim that wiped out settlements and decimated lives are attributed to a GLOF.
Sediment deposition: River beds become shallow due to sedimentation. The water-carrying capacity of such rivers is reduced. As a result, the heavy rainwater overflow the river banks.
- Frequent floods were observed in 2003, 2008, 2011, and 2013 near the deltaic region of the Mahanadi river due to the excessive sediment deposition.
Tropical cyclones and hurricanes: These powerful weather systems often bring heavy rainfall and storm surges, resulting in widespread flooding in coastal and low-lying areas.
- Recently, Cyclone Asna contributed to heavy rainfall and flood situations along coastal areas of Gujarat.
Change in the course of the river: Meanders, erosion of river beds and banks, and obstruction of flow due to landslides also lead to changes in river courses.
- The 2008 Kosi River flood resulted from heavy rainfall and a subsequent course change, leading to catastrophic flooding, displacement of thousands, and widespread damage in Bihar, India.
Tsunami: Large coastal areas are flooded by rising sea water, when a tsunami strikes the coast.
Lack of Lakes: Lakes can store the excess water and regulate the flow of water. When lakes become smaller, their ability to regulate the flow become less and hence flooding.

Anthropogenic causes

Deforestation: The removal of trees and vegetation reduces the natural absorption of rainfall, leading to increased surface runoff and a higher likelihood of flooding.
- The devastating floods that hit the state of Kerala in 2018 were partially attributed to deforestation, as the loss of forest cover reduced the natural water-holding capacity of the region.
Urbanisation: Construction of buildings, roads, and other infrastructure reduces natural permeable surfaces, which can exacerbate surface runoff and overwhelm drainage systems.
- Chennai experienced severe flooding in 2015 due to heavy rainfall combined with unplanned urbanisation. The city’s drainage systems were overwhelmed, resulting in widespread inundation and disruption.
Land use changes: Alterations in land use, such as converting natural wetlands into agricultural or urban areas, can disrupt natural water retention and drainage patterns, increasing the risk of flooding.
Dam failures: Structural failures or breaches in dams and reservoirs can release large volumes of water downstream, causing severe flooding.
- In 2019, the collapse of the Tiware Dam in Maharashtra caused flash floods in downstream villages.
Interference in drainage system: Drainage congestion caused by badly planned construction of bridges, roads, railway tracks, canals etc. hampers the flow of water and results in floods.

Distribution of Flood Prone Areas in India

The Brahmaputra River Region	This region consists of the rivers Brahmaputra and Barak and their tributaries, and covers the states of Assam, Arunachal Pradesh, Meghalaya, Mizoram, Manipur, Tripura, Nagaland, Sikkim and the northern parts of West Bengal. The catchments of these rivers receive heavy rainfall during monsoons. These rivers originate in fragile hills susceptible to erosion leading to high silt discharge. The region is subject to severe and frequent earthquakes, which cause numerous landslides and upset river regimes. Cloud bursts followed by flash floods and heavy soil erosion are also prevalent.
The Ganga River Region	The river Ganga has many tributaries, the important ones being Yamuna, Sone, Ghaghra, Raphti, Gandak, Burhi Gandak, Bagmati, Kamla Balan, Adhwara group of rivers, Kosi and the Mahananda. It covers the states of Uttarakhand, Uttar Pradesh, Jharkhand, Bihar, south and central parts of West Bengal, Punjab, parts of Haryana, Himachal Pradesh, Rajasthan, Madhya Pradesh and Delhi. The flood problem is mostly confined to the areas on the northern bank of the river Ganga as most of the damage is caused by the northern tributaries of the Ganga. In general, the flood problem increases from the west to the east and from south to north. Large-scale encroachment of flood plains of the rivers for habitation and various developmental activities is one of the main causes in this region.
The North-West River Region	The main rivers in this region are the Indus, Sutlej, Beas, Ravi, Chenab and Jhelum. This region covers the states of Jammu and Kashmir, Punjab and parts of Himachal Pradesh, Haryana and Rajasthan. Compared to the Ganga and the Brahmaputra river regions, the flood problem is relatively less in this region. The major problem is that of inadequate surface drainage which causes inundation and water-logging over vast areas. Indiscriminate use of water for irrigation and development of low-lying areas and depressions has created problems of drainage congestion and water logging. These rivers change their courses frequently and leave behind vast tracts of sandy waste.
The Central and Deccan India	Important rivers in this region are the Narmada, Tapi, Mahanadi, Godavari, Krishna and Cauvery. These rivers have mostly well-defined and stable courses. They have adequate capacities within the natural banks to carry the flood discharge except in the delta area. The region does not have serious flood problem except that some of the rivers in Orissa State namely Mahanadi, Brahmini, Baitarni, and Subarnarekha are prone to floods every year. The delta and coastal areas of the states on the east coast periodically face flood and drainage problems in the wake of monsoon depression and cyclonic storms.

Consequences of Floods

Loss of life and injuries: Floods can result in the loss of human lives and cause injuries, especially when people are caught unaware or unable to evacuate in time.
Damage to infrastructure: Floodwaters can cause severe damage to roads, bridges, buildings, and other infrastructure. This damage can disrupt transportation networks, communication systems, and essential services, making rescue and relief operations challenging.
Displacement and homelessness: Floods often force people to evacuate their homes and seek shelter in temporary accommodations or relief camps.
Impact on agriculture and food security: Floods can devastate agricultural lands and crops, destroy livestock leading to significant losses in the agricultural sector.
Water contamination and health risks: Spread of diseases like cholera, gastro-enteritis, hepatitis and other water-borne diseases spread in the flood-affected areas.
Environmental damage: Floods can cause erosion, sedimentation, and the destruction of natural habitats.
Soil fertility: Floods also make a few positive contributions. Every year, flood deposit fertile silt over agricultural fields which restores fertility of the soil.

Need for Flood Management

During the monsoon season, approximately 350,000 million gallons of water flow into the Yamuna daily. Preserving this water could supply Delhi residents with drinking water for a year.
In November 2022, the floodwater released into the sea in Chennai could have met the city’s water needs for half a year.
Floodwater can be conserved to address drought and water scarcity during the summer months.
Per capita water availability in India has sharply declined from 5,177 cubic metres per year in 1951 to 1,486 cubic metres in 2022, with a further projected decline to 1,367 cubic metres by 2031.
The Union Ministry of Housing and Urban Affairs reports that per capita water consumption is 135 litres in urban areas and 55 litres in rural areas.
Two-thirds of India’s 718 districts face significant water scarcity issues.
Growing awareness of safe drinking water has led to a rise in spending on bottled/packaged water, with 12.2% of urban households relying on it in 2018, up from 2.7% a decade earlier. In rural areas, consumption increased from 0.5% in 2008 to 4% in 2018.
Empirical evidence underscores the necessity of managing rainfall productively to combat water scarcity.

Flood Prevention and Mitigation

Structural Measures

Dams and Reservoirs: Construction of dams and reservoirs to store excess water during heavy rainfall and release it in a controlled manner, reducing downstream flood risk.
Levees and Floodwalls: Building embankments, levees, and floodwalls along rivers and coastlines to contain floodwaters and protect adjacent areas from inundation.
Flood Diversion Channels: Creation of diversion channels or canals to redirect excess water away from vulnerable areas, reducing flood impact.
Flood Control Basins: Designing flood control basins or detention ponds to temporarily store and regulate floodwaters, preventing their rapid downstream flow.
Channelization: Modifying and straightening river channels to improve their flow capacity and efficiency, reducing the risk of overflow and flooding.
Floodplain Restoration: Restoring natural floodplains by removing obstructions, reconnecting floodplain habitats, and creating additional space for water storage during floods.

Non-Structural Measures

Floodplain Zoning and Land Use Planning: Implementing zoning regulations that restrict construction in high-risk floodplain areas, ensuring that development is appropriately located and mitigating potential flood damage.
Early Warning Systems: Establishing robust early warning systems that use technology and community engagement to provide timely alerts and evacuation guidance to vulnerable populations.
Flood Insurance and Financial Mechanisms: Promoting the availability of flood insurance to incentivize risk reduction measures and provide financial protection to individuals and businesses affected by floods.
Public Awareness and Education: Conducting public awareness campaigns to educate communities about flood risks, safety measures, and preparedness strategies, fostering a culture of resilience.
Urban Drainage Systems: Developing and maintaining efficient stormwater drainage systems in urban areas to manage excess rainfall and prevent waterlogging and urban flooding.
Ecosystem-Based Approaches: Preserving and restoring natural ecosystems, such as wetlands and mangroves, which act as natural buffers and absorb floodwaters, reducing flood impacts.
Integrated Water Resources Management: Adopting an integrated approach to water resources management that considers the entire watershed, balancing water allocation, flood control, and environmental sustainability