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Why Do Floods Occur? Here Are 13 Causes of Floods and How to Prevent Them

Every time it rains heavily, concerns about flooding often follow. Heavy rains continuously falling can cause rivers to overflow and submerge streets, affecting residents.

Although often considered a natural disaster, flooding is not always caused solely by natural factors. Human activities such as throwing garbage into rivers or the reduction of floodplain areas can worsen this condition. Then, what are the real causes of flooding and how to prevent them?

Let’s discuss further!

What is Flooding According to Experts?

Generally, flooding is an event when water overflows and submerges land that is usually not covered by water.

According to the Kamus Besar Bahasa Indonesia (KBBI), flooding is defined as water in large quantities and rapidly flowing, especially from rivers, flooding areas that are usually dry.

To understand flooding more deeply, several experts have provided definitions explaining this phenomenon from different perspectives. Below are several definitions of flooding according to experts:

• Ligal (2008): Flooding is an event when land that is usually dry (not an area that is constantly wet) becomes submerged with water. This condition is usually caused by heavy rainfall and topography of lowland or depressions.
• Khotimah dkk. (2013): Flooding is the flow or submergence of water that can cause economic losses and lead to casualties. In technical terms, flooding occurs when the flow of river water exceeds the capacity of the river’s retention basin.
• Rahayu (2009): Flooding is defined as a situation where an area becomes submerged due to water overflow exceeding the capacity of drainage systems in that area, causing physical, social, and economic losses.

The Types of Flooding

Flooding does not occur in just one form. This phenomenon has several types that differ based on the water source and characteristics of its flow. Each type of flooding also has different risk levels, speed of occurrence, and impacts, requiring adaptation in response measures to the conditions on the ground.

Generally, flooding can be categorized based on the water source and type of water submerging the area.

Here are the types of flooding:

Based on Water Source

According to Ristya (2012), flooding can be categorized into two types based on its water source:

1. Local Flooding

Local flooding occurs due to heavy rainfall in a specific area, while drainage systems in place cannot handle the volume of water. As a result, rainwater submerges the surrounding areas.

Since it is localized, local flooding usually only affects areas that receive the heavy rain.

Several factors that commonly trigger local flooding include:

• Extremely high rainfall intensity in a short period
• Limited capacity of drainage systems
• Drainage channels clogged by garbage or sediment

2. Transient Flooding

Unlike local flooding, transient flooding occurs when river water volume increases due to water flow from upstream areas. In other words, the affected area may not experience heavy rain but is still impacted by the water flow from other areas.

As a result, river flow increases and floods the lowland areas.

Several conditions that can worsen transient flooding include:

• Reduced floodplain areas in upstream regions
• Increased development in watershed areas
• Changes in land use that cause more water to flow on the surface

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Based on Water Type

When viewed from the type of water or materials carried, flooding can also be categorized into several types as follows.

1. Water Flooding

Water flooding is the most common type of flooding, especially in urban areas or lowland regions. This usually occurs due to river overflow, lakes, or drainage systems that cannot handle the volume of rainwater.

The main characteristic of water flooding is water accumulation that forms gradually after rain continues to fall over a long period.

2. Debris Flooding

Debris flooding is a type of flooding that arrives very quickly and has high destructive power.

Because it carries a lot of heavy materials, debris flooding can damage houses, bridges, and other infrastructure. This type of flooding often occurs in areas near mountains or terrain with steep slopes.

The flowing water usually carries various materials such as:

• Rocks
• Sand and gravel
• Twigs
• Debris from buildings

3. River Flooding

River flooding occurs due to coastal flooding caused by rising sea levels. This usually happens in coastal areas or regions with lower elevation than sea level.

As a result, seawater submerges residential and infrastructure areas near the coast.

Several factors that can trigger coastal flooding include:

• High sea tides
• Declining land elevation in coastal areas
• Rising sea levels

4. Cold Water Flooding

Cold water flooding occurs in areas around volcanoes.

This material is usually carried by heavy rains that flow down mountain slopes. Because it carries a lot of dense materials, cold water flooding has very high destructive power and can damage residential areas, agricultural land, and infrastructure nearby.

The flow consists of a mixture of water with volcanic materials such as:

• Volcanic ash
• Sand and gravel
• Rocks
• Residues from eruptions

13 Main Causes of Flooding

Many people believe flooding only occurs due to heavy rains. However, the reality is more complex. Flooding usually happens due to a combination of various factors, starting from natural conditions to human activities that disrupt the environmental balance.

Besides high rainfall, factors like topography, soil absorption capacity, and poor environmental management can also increase the risk of flooding. Below are the main causes of flooding that should be known:

1. High Rainfall

Heavy rainfall lasting a long time can make the soil unable to absorb all the water that falls. When the soil’s absorption capacity is full, water will flow on the surface and potentially cause flooding.

High rainfall intensity can also cause river water to rise quickly, increasing the risk of flooding in surrounding areas.

2. Low Topography of the Area

Areas with low topography are more prone to flooding. Flat areas cause water to accumulate and flow more slowly compared to higher areas.

In addition, several other factors can worsen this condition, such as:

• High groundwater table
• Specific soil types that are difficult to absorb water
• Location close to rivers or other water bodies