What is flooding?

Flooding is a temporary overflow of water that submerges or covers the the usually dry land. It can also be defined as the overflow of the excess amount of water that covers a huge area of land which is normally dry.

Causes of flooding

Flooding can be caused due to following reasons:

• Heavy precipitation
• Overflowing rivers
• Urban drainage basins
• Broken dams
• Storm surges and tsunamis
• A lack of vegetation
• Deforestation
• Cyclones
• A rise in the river bed
• Melting snow and ice
• Earthquake and landslide

Types of floods

Flood is classified into the following types:

• Areal flooding
• Channel flooding
• Flash flooding
• Coastal flooding
• Urban flooding
• Catastrophic flooding

Areal flooding

Areal flooding begins in flat areas such as floodplains or depressed areas. When it rains continuously, after the limit of infiltration of water in the soil exceeds, the excess water accumulates on the floodplain, resulting in flooding.

Channel flooding

Channel flooding occurs due to the overflowing of rivers, streams, or channels. Due to intense rainfall or melting of snow when the water bodies exceed their capacity, the excess water rises on the floodplain, which causes flooding.

Flash flooding

Flash flooding occurs due to the accumulation of water into water bodies or on land because of intense rain over a short period. Because of intense rainfall in a short period, the drainage system gets flooded and the water accumulates on the land.

Coastal flooding

Coastal flooding occurs in coastal regions. It happens when a rainstorm combines with high tides and large waves, resulting in a rising sea level in the coastal areas, which causes the rising of water level on the floodplain, hence causing flooding.

Urban flooding

Urban flooding occurs in populated urban areas due to intense rainfall, overflowing of rivers, or cloud bursting. The impervious surfaces in urban areas prevent water from percolating into the ground and hence, the water gets saturated on the land.

Catastrophic flooding

Catastrophic flooding is caused due to infrastructure failure. Due to landslides, earthquakes, or volcanic eruptions, the infrastructures such as dams, their spillways get damaged and collapse, due to which the stored water floods the floodplains first and then the main region.

Flooding can be further classified into the following types:

• Fluvial flooding
• Pluvial flooding

Fluvial flooding

Fluvial flooding is the term used when rivers or streams get flooded due to excessive rain or snowmelt.

Pluvial flooding

Pluvial flooding is the term used when extreme rainfall causes flooding irrespective of the assistance of flowing water bodies.

Effects of flooding and flood control

Floodplains are the regions most affected by floods. The flood causes loss of lives. Hence, the people living in flood-prone regions and near floodplains need to ensure flood insurance to get security against flood hazards. Flood insurance helps aftermath of the flood event. Flood also causes economical loss of the region by destroying all the structural and nonstructural parts of infrastructures in the region. Structural parts cause more economical loss as compared to nonstructural parts. Hence, it is necessary to control the flooding by proper flood management. It is necessary to use proper strategies while working on flood risk management. Flood management of floodplains is very crucial as floodplains tend to get flooded first during any flood event.

Flood control planning

Flood control planning is a necessary part of flood management, used for developing techniques for flood control. The planning is done with proper strategy and includes the following:

• Analysis of previous flood data and real-time situations of flood heights.
• Model analysis of the hydrological structures present.
• Designing structures to control the flooding or resist flooding.
• Proper forecasting and monitoring of weather and floods with the help of Meteorological departments.

Flood control techniques

Various techniques are developed with proper strategy as a part of flood management by experts. The easiest method is the use of sandbags in every home. Given below are the techniques used worldwide on a large scale for reducing the flood hazard from any flood event.

Dams and reservoirs

Dams are built to store water and reservoirs are built to distribute the stored water through spillways into fields and other water bodies. The provision of dams and reservoir helps in suppressing the flooding conditions as the excess rainwater is stored in the dams and reservoirs and hence helps in flood control.

Diversion canals

Diversion canals are also known as floodways. They are connected to rivers and other water bodies. The diversion canals are used to diverge water from water bodies during flooding conditions and help in flood control. During a flood, the water is diverted from the flooded water bodies to temporarily created ponds using diversion canals.

River defenses

Various river defenses are developed for protection from floodwater. The defenses include levees, weirs, and floodwalls.

A levee is a berm constructed on the banks of rivers either naturally by the alluvial deposits by the flowing rivers or by constructing them naturally for protection against flooding.

Weirs are also known as low head dams. Weirs are constructed along the width of the river to resist the flow of the water for protection against flooding.

Flood walls are the artificial vertical walls constructed along the banks of the river to prevent the overflowing of water during extreme weathering conditions.

Coastal defenses

Coastal defenses are the structures developed on the coastal regions to protect against flooding of the coastal regions from floodwater generated due to rising sea levels. The various coastal defenses include sea walls, beach nourishments, barrier islands, and tide gates.

Flood tunnels

Flood tunnels are structures that are mostly created in urban areas where there is a lack of space to create channels. In this technique, an underground tunnel is created, which carries the floodwater and takes it where there is no threat, and protection of the region is done.

Anti-flood reservoir

In an anti-flood reservoir system, the flood water and excess surface water are stored in an underwater reservoir. During normal conditions, the water is released back into the water bodies in a controlled manner.

Sponge city

Sponge city is an advanced technique used for flood management and protection from flooding. The sponge city is a special structure designed in such a way that the water from rainfall is absorbed into the ground, stored, and utilized to reduce flood.

Context and Applications

The concepts of flood control are useful for the students undergoing the following courses:

• Bachelors in Technology (Civil Engineering)
• Masters of Technology (Water Resources Engineering)

Practice Problems

1. Which of the following is not a reason for flooding?

1. Heavy precipitation
2. Drought
3. Cyclones
4. Deforestation

Answer– b

Explanation – Drought is not a reason for flooding.

2. Which of the following is not a type of flooding?

1. Channel flooding
2. Areal flooding
3. Urban flooding
4. Perimetric flooding

Answer– d

Explanation – Perimetric flooding is not a type of flooding.

3. Which of the following terms is used when extreme rainfall causes flooding irrespective of the assistance of flowing water bodies?

1. Coastal flooding
2. Pluvial flooding
3. Fluvial flooding
4. Catastrophic flooding

Answer– b

Explanation – Pluvial flooding is the term used when extreme rainfall causes flooding irrespective of the assistance of flowing water bodies.

4. Which of the following structures are mostly created in urban areas where there is a lack of space to create channels?

1. Flood tunnels
2. Coastal defenses
3. River defenses
4. Dams

Answer– a

Explanation – Flood tunnels are mostly created in urban areas where there is a lack of space to create channels.

5. Which of the following is an advanced technique used for floodwater management?

1. Bubble city
2. Rubber city
3. Sponge city
4. Pipe city

Answer– c

Explanation – Sponge city is an advanced technique used for floodwater management.