Disaster risk management: Floods

Here is a town in a river valley. When there’s rain in the forecast, the residents of this town get a little nervous! There is always a risk that heavy rain here will cause the river to break its banks, causing a flood. What can be done? It is not always possible to stop a flood.

But, we can stop floods from becoming disasters by preparing ahead of time. There are several strategies these townspeople use to manage and control flood waters. One strategy is building barriers to hold the water back. The first type is built using compacted soil, grass, sand or other natural elements - it is a levee. Levees are usually found along the banks of rivers, and act like hills to keep water from immediately rising into the local area.

Floodwalls have a similar purpose, but are instead built of manmade materials, such as concrete. A floodwall may look like a regular garden wall, but it is strengthened from the inside with steel bars, and has a very deep foundation. This stops the wall from tipping over, and prevents water from seeping through underneath. Floodwalls don’t require a big slope, so they may be a better choice than levees in places where space is limited, such as cities. A man-made pathway has also been built here, to act like a river for the extra water to go.

This is called a flood diversion channel. This smooth, wide channel can quickly carry a lot of water away from where it might flood homes and other buildings. While these can reduce flood risks, they are not perfect. All floods are different. Just because a levee or floodwall has resisted floods in the past, does not mean it will be safe from the next flood!

It is always possible that a flood can bring more water than a levee or floodwall can handle. Diversion channels, meanwhile, can become blocked. They might even cause flooding in the areas they redirect their water to. That is why the townspeople need to constantly check and maintain their levees and floodwalls. Some floods happen unexpectedly, without warning.

Others are more predictable, happening at the same time every year. So, when it comes to managing flood risk, it’s important to have a good understanding of the weather and the environment. The process of predicting when and where floods might happen and how severe they could be is called flood forecasting. It begins with collecting a lot of data! Weather forecasting agencies throughout the world are always monitoring weather conditions, rainfall amounts, water levels in rivers, and more, using computer models and data from satellites.

The townspeople also use information about past floods to understand the current state of the environment. Based on the forecasts and models, experts issue flood warnings and alerts. Things like text messages, TV announcements, and social media can be used to warn people about floods and what they should do to stay safe. In this town, residents may have to leave their homes temporarily and go to safer places. This is called evacuation.

It's done to make sure people are not in danger from rising water levels. Flooding can be dangerous! That’s why quick and coordinated communication is very important during a flood. With effective disaster risk management, the impact of floods on people can be reduced.