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The economics of flood insurance
The economics of flood insurance

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1.1 What is Flooding?

Flooding occurs when an area not normally covered in water is temporarily inundated.

Satellite image of The River Nile
Figure 1 The River Nile, Red Sea and Mediterranean coast
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Satellite image of The River Nile

Figure 1 The River Nile, Red Sea and Mediterranean coast

Rivers can flood, for example, as a result of heavy rainfall or in the spring when snow melt from higher altitudes leads to a sudden increase in the volume of water. But flooding is not something that only happens in communities located next to rivers or coastlines. There are six common types of flooding (Flood Guidance, 2009), some of which can even affect hill-top locations. Explore the types of flooding by scrolling/rolling over/clicking on the images in Figure 2.

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Figure 2 Types of flooding
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Slide 1 shows a drawing of a landscape. There are mountains and trees on the background. On the sky there are clouds with heavy rain. On the front there is a turbulent river. Text reads: River (or fluvial) flooding: This type of flooding occurs when a river exceeds its bank sides. It is particularly dangerous, because the current of the river can mean the flood water is fast flowing. Even shallow water can move large objects (like a car) if the water is fast flowing.

Slide 2 shows a drawing of a landscape. There is the sun on the horizon and some seagulls flying. On the front there is a sandy beach with a couple of palm trees. The sea is a bit turbulent and one can see that there are water pools on the sand.Text reads: Coastal (or tidal) flooding: This type of flooding occurs when seawater over tops coastal defences and requires local communities to retreat further inland. It is particularly damaging, because the sea salt in the flood water damages buildings and can cause salination of soil and groundwater.

Slide 3 shows a drawing of a landscape. There are three houses and some garden plants on the background. The sky is clear with only two clouds. On the front there is a lot of water reaching as high as the middle of the doors in the houses. Text reads: Surface water (or pluvial) flooding: This type of flooding can happen even if a community is not located near a river or the sea. Heavy rainfall creates surface water that cannot drain away. This may be because drains are blocked or inadequate or because areas have become built up and reduced the efficiency of the natural drainage capacities.

Slide 4 shows a drawing of a landscape. The ground level is visible as well as above and below it. On the over ground there are three puddles of water. On the underground there is a lot of water, reaching up to the ground level. Text reads: Groundwater flooding: This type of flooding occurs when rainfall raises the water table in an area, so that if the water table rises up through a slope, it may reach a point where the water table is higher than the ground level. This means that water can no longer seep into the ground but collects as groundwater or pours down from water-logged higher ground. It may require communities to consider flood management measures that prevent water from rising up from below their properties.

Slide 5 shows a drawing of a landscape. There is a main sewage pipe on the background. It is spilling water to the foreground. On the front there are some rocks that are partially submerged in water. Text reads: Sewer flooding: This type of flooding usually occurs when a sewage pipe is blocked or flooded with rainwater. It is particularly dangerous, because the contents of the flood water contaminate the areas inundated. Professional clean-up is necessary to ensure the health risks are minimal.

Slide 6 shows a drawing of a landscape. There are three dam gates on the background. They are all showing a heavy outflow of water. On the front there is turbulent water with a high level. Text reads: Reservoir flooding: This type of flooding occurs when the dams holding reservoir water back fail and water flows down the natural water path. It is particularly dangerous, because there is a large volume of water involved, which flows fast and can only be avoided by reaching higher ground.

Figure 2 Types of flooding
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Activity 1 Is flooding a problem?

Timing: Allow 10 minutes for this activity

Thinking about the types of flooding described in Figure 2, would you consider some types to be more or less problematic than others? Are there any types of flooding that might be beneficial?

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Answer

All types of flooding may be problematic, depending on context. There may be loss of life, damage to property, impact on infrastructure, such as roads and rail systems, bridges and power lines. Sewer flooding, because of contamination, poses additional dangers to health. Depending on the severity and duration of the inundation, these different aspects of damage may exacerbate each other (such as in cases where large scale flooding makes roads impassable, making it difficult to rescue people or get healthcare to them).

On the other hand, flooding may be predictable, expected and harmless. If there is an adequate flood plain to take up the water from river or coastal flooding, it might not be particularly problematic. The flood can simply be left to dissipate over time.

Flooding may even be beneficial to natural or agricultural processes. Civilisation has thrived for thousands of years around the Nile in Egypt, strongly benefitting from agriculture on the flood plains. The annual silt and water deposits make the land extremely fertile. Flooding is therefore not an inherently negative event, but can be problematic if unpredictable, unexpected or badly managed.