Flood (Disaster Management)

The term “flood” is commonly used to describe a situation where the water flowing in rivers, streams, and other bodies of water cannot be contained within natural or artificial banks. 

Floods occur regularly in India, affecting approximately 10% of the country’s total area. However, the impact and frequency of floods have increased due to climate change.

Natural Causes

• Heavy precipitation: India receives all the rainfall in just 4 months. During that period, the discharge of water in the river increases than the capacity of the river, resulting in floods.
• The river changes its course due to various reasons, such as landslides. By blocking the flow of streams, the landslides cause massive floods.
• Events such as cloud burst, which results in massive water discharge in a very less period
• Climate Change: Climate Change led to increased variability in rainfall patterns, with some areas experiencing prolonged dry spells followed by heavy rainfall in a short period. This change in rainfall patterns contributes to flash floods.

Manmade Causes

• Settlement in Flood Plains: Many towns and cities have been established in floodplains, which are low-lying areas adjacent to rivers and prone to flooding during heavy rainfall or when rivers overflow their banks.  E.g., Construction activities in low-lying areas, such as Alapuzha in Kerala, have made these regions highly vulnerable to flooding.
• Destruction of Natural Wetlands around the Cities: Wetlands play a vital role in controlling floods by acting as natural sponges that absorb excess water during heavy rains. However, the destruction and encroachment of wetlands for urban development and agriculture have significantly reduced their capacity to absorb and store water. 
• Environmental Degradation: The Gadgil report on the fragile ecosystem of the Western Ghats, released in 2011, highlighted the detrimental effects of illegal mining and deforestation in the region. These activities have led to extensive encroachment on river fronts, resulting in reduced river carrying capacity and increased siltation in reservoirs located in the Western Ghats. 
• Deforestation and Soil Erosion: Deforestation, particularly in hilly regions and catchment areas, has a significant impact on flooding in India. Trees and vegetation help to retain rainwater, reduce surface runoff, and stabilize the soil. When forests are cleared for agriculture, urban expansion, or other purposes, the protective cover is lost, leading to higher rates of soil erosion. Increased soil erosion results in more sediment being carried by rivers, leading to siltation and reduced carrying capacity, which in turn contributes to floods.
• Faulty Dam Management: Dam failures, the release of excessive water during heavy rainfall, or sudden discharges without adequate warning can lead to downstream flooding.  The 2018 floods in Kerala revealed shortcomings in dam management. The dam authorities were unable to assess the situation accurately and failed to provide timely warnings to the affected communities.

Flash floods are an extreme manifestation of flooding that takes place within a significantly compressed timeframe, resulting in rapid and intense inundation. Unlike conventional floods that may unfold over a longer period and affect larger regions, flash floods are highly localized. 

Causes of Flash floods in India

1. Cloudbursts: Cloudbursts are sudden, intense rainfall events that occur within a short period in localized areas that overwhelm drainage systems.
2. The concentration of rainfall during the monsoon season: India receives nearly 75 per cent of its total rainfall during the monsoon season. This concentrated rainfall puts a significant burden on the rivers.
3. Water exceeding the Dam’s Capacity: Flash floods can also occur when the water level in a dam exceeds its capacity. 
4. Glacial Lake Overflow: In regions with glaciers, flash floods can be triggered by the overflow of glacial lakes. 

Factors like poor drainage infrastructure, deforestation, and urbanization can also exacerbate the risk of flash floods in certain areas.

Hard Management Techniques

1. Dams: Dams play a crucial role in flood management by trapping and storing water during heavy rainfall or snowmelt periods. The stored water can then be released gradually during dry spells.
2. Embankments or Artificial Levees: These structures are built along riverbanks to contain floodwaters within the river channel, preventing them from spilling into surrounding areas. 
3. Interlinking of Rivers: Connecting rivers through canal systems or diversion channels can help manage floods by diverting excess water from one river to another.
4. Flood Walls/Coastal Defences: These structures are constructed around settlements, particularly in coastal areas, to protect them from the impact of floods and storm surges.  
5. Storage Areas: Constructing temporary storage areas, such as reservoirs or lakes, allows excess water to be pumped out of rivers during flood events.
6. Dredging the River Basins: Dredging involves removing sediments, debris, and vegetation from river channels, increasing their capacity to carry water. 

Soft Management Techniques

1. Washlands: Certain sections of the floodplain, known as washlands, are intentionally allowed to flood. These areas are often designated as sports fields or nature parks, serving as controlled flood zones.
2. Flood Plain Zoning: This technique involves establishing regulations and land-use policies that restrict or discourage development in flood-prone areas.
3. Afforestation: Planting trees and vegetation in flood-prone areas can help manage floods. The roots of trees absorb water and stabilize soil, reducing erosion and the likelihood of flash floods. 
4. Warning Systems: Implementing early warning systems can provide timely information about impending floods.
5. Hydrological Data Sharing: Cooperation and sharing of hydrological data among countries in the upper catchment area of a river basin are vital for effective flood management.

Capacity Building

1. Flood Education: Raising awareness and providing education about floods, their causes, and appropriate responses can empower communities to better prepare and respond to flood events. 
2. Emergency Search and Rescue: Developing specialized search and rescue teams trained in flood response can significantly improve emergency operations. 
3. Emergency Relief: In the aftermath of a flood, providing short-term housing, food, safe water, access to healthcare, and protection for vulnerable groups such as women, children, and the elderly is essential. 

Other Measures

1. There is a need to promote flood-tolerant “scuba rice”, sugarcane, jute and high-value aquatic crops in regions frequently hit by floods. 
2. Formulate Nation-wide Silt Management Policy.