What are floods?

What are floods?

Floods are partial or total occupations of water that occur on a surface that is usually dry and that could generate material and / or human damage.

Floods are events produced by natural phenomena such as rains, hurricanes, or snow melt; or produced by human activity.

Types of floods

There are various classifications of floods according to the various official disaster prevention agencies. This is a compilation of all categories:

Flash floods ( flash floods )

These are events in which water accumulates and saturates the terrain in a very short period. Generally they are floods caused by precipitations of sudden appearance but of intense effect. That is, rains that are generated suddenly and that also last a long time.

Flash floods are considered one of the most dangerous categories, since by their nature they make prevention and eviction tasks difficult for affected populations.

One of the most outstanding characteristics of flash floods is that they tend to be generated in terrain with steep slopes. This facilitates the rapid descent of the water and the flooding of the terrain, with the structural and human damages that this implies.

Slow floods

They are generated by persistent rains that can be intense or moderate, which causes a progressive saturation of the terrain. In these cases, rainfall can last between two and four days at least.

The persistent nature of rainfall can cause material damage to poor structures, as well as damage crops and crops. However, in this case it is possible to activate damage prevention and containment protocols because the time frame is longer.

River floods

River overflow is one of the most common causes of recurrent flooding in third world regions.

They are floods caused by the overflow of rivers, either due to problems associated with the quality of the land on their banks or due to a considerable increase in flow.

This increase in the water level can be caused by intense or prolonged rains, or by the melting of snow in areas near the river.

Storm floods

Satellite view of the Ayatthaya region before and after the floods caused by the monsoon rains in Thailand in 2001.

It is any saturation of terrain caused by rains. In some countries, flooding from pluvial sources is a constant at certain times of the year, as in India, whose rains caused by monsoon winds generate large floods during the summer.

Coastal flooding

If barrier floods exceed sloping terrain, a flash flood or flash flood may occur .

These are events caused by the rise of the sea, which ends up entering the mainland, either by the effect of heavy rains, tidal waves, tsunamis, storms or typhoons. In this sense, coastal floods can occur in one of three ways:

  • Direct: water directly breaks the ground in the absence of natural or artificial barriers.
  • Barrierbreak: water breaks a natural or artificial barrier as a result of strong waves.
  • Excess barrier: the size of the waves or the tide overcomes a barrier, either natural or artificial and floods the terrain.

Urban floods

The accumulation of waste is one of the causes of floods in urban areas.

They are a type of flood that affects urbanized cities and communities. They can have a natural origin (rainfall or overflow of rivers) or artificial (failure in hydraulic works, breakage of levees, etc.).

Population density, soil erosion, and increased garbage production are just some of the factors causing urban flooding.

You may be interested in reading: Natural disasters.

Flood causes

Floods can have various causes. These are the events or activities that can cause flooding:

Natural causes

They have to do with natural events that occur without human intervention, such as:

  • Rains: they generate a saturation of water in the land that, by not draining quickly, causes flooding.
  • Meltingice: the condensation of the ice causes the water to reach the rivers and increase their channel, causing their overflow.
  • Storms, hurricanes, typhoons or tsunamis: they generate waves of great magnitude that can knock down natural or artificial barriers, facilitating the entry of water on dry land at high speed, and flooding everything in its path.

Unnatural causes

They are factors related to human activities that have a direct impact on water bodies or on the decrease in the quality of the land. Some of those activities are:

  • Hydraulic faults: ruptures of dams or dams, which release large amounts of water in a very short time, saturating the terrain or nearby bodies of water and causing flooding.
  • Water contamination:solid waste and sewage can obstruct the channels of the water bodies, favoring their elevation and subsequent overflow.
  • Soil erosion: urban works, excess crops or pollution decrease the quality of the land, increasing its permeability, making it susceptible to saturation more quickly.

Consequences of the floods

Floods have an impact on multiple levels, and end up affecting not only the environment but also local and national economies.

Environmental consequences

Floods can generate slight, moderate or severe changes in the affected topography. These changes in terrain can be part of natural dynamics (such as monsoon rains) or human activity, and can affect local ecosystems.

If a crop is devastated by a flood, the ecosystem of which it was part is also altered. Pollinating agents (such as bees) and animals that have benefited from crops for food can move to other areas and negatively alter this new location.

Economic consequences

Floods can cause considerable structural damage, affecting homes, commercial premises, crops. All this has a negative impact on the local economy, which in turn deteriorates the living conditions of the affected people.

In 2017, monsoon rains flooded tea crops in Darjeeling, India. The loss of the crop had an impact on the Indian economy and increased the value of Indian tea worldwide, hurting final consumers.

Social consequences

In the most serious cases, floods can cause human loss or serious injuries. Furthermore, these types of events can induce forced population displacement, as a way to solve the loss of the home or the source of work.

It is also possible that the authorities order the suspension of educational, work or recreational activities, which directly impacts the quality of life of people.

Health consequences

Floods can generate foci of diseases such as dengue, infectious, dermatological diseases, digestive disorders, etc.

In the most disadvantaged areas, this type of situation worsens the already precarious conditions of the local health systems, by collapsing their attention capacity.

Examples of floods in Latin America

In Latin America there are several examples that illustrate the magnitude that a flood can reach, especially when adequate prevention or containment measures are not taken.

These are just some of the most relevant events that have occurred in recent history:

Tragedy of Vargas, 1999 (Venezuela)

During the month of December, the intense and prolonged rains that occurred throughout the country generated an unprecedented landslide in the Vargas state. This situation left a balance of more than 300 thousand victims, thousands of deceased, wounded and disappeared, in addition to irreparable structural damage.

Santa Fe Flood, 2003 (Argentina)

A persistent and intense rain that occurred at the end of May in the city of Santa Fe and nearby towns, generated a flood of the Salado River. The water managed to penetrate the defenses (which were not finished) and entered the city, causing human and material losses.

Tabasco Flood, 2007 (Mexico)

A series of continuous precipitations accelerated the flooding of the Usumacinta and Grijalva rivers, flooding 80% of the state of Tabasco.

The levees and barriers were surpassed by the waters, which brought about the collapse of drinking water, electricity and health services, as well as human losses and victims.

Tragedy of Mariana, 2015 (Brazil)

During the month of November, a dam built to hold toxic waste in the city of Mariana, in the state of Minas Gerais, leaked. A few hours later, the dam gave way and expelled contaminated sludge that reached the Doce River, which supplied drinking water to the entire state.

This situation caused not only the overflow of the river and the flooding of nearby towns. It also caused irreparable damage to the drinking water system, since it is now not suitable for consumption.


by Abdullah Sam
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