What Is a Flash Flood?

The following essay is covered in The Conversation, an online publication.

The type of flooding that occurs in a short time frame after a precipitation event is called flash flooding. Heavy or excessive rain can cause it, but it can also happen in places with no water bodies nearby.

There are flash floods in rural and urban areas. The water can rise very quickly in areas with a lot of impervious surfaces that prevent the ground from absorbing the precipitation.

The soil may not be able to absorb any more water if an area has recently had a lot of rain. When soil is too dry and hard to absorb precipitation, it can cause flooding. Areas with shallow soil depths above solid bedrock are prone to flash floods after heavy rains.

The lowest point in a potential pathway will be the focus of the rain. In urban areas, that is often streets, parking lots and basement. In rural areas with steep terrain, flash flooding can turn creek and river into raging torrents.

Even though weather forecasters and emergency personnel try to warn, flash floods can catch people by surprise. Cars can be washed away and buildings can be moved.

To be safe in a flash flood, you need to be aware of the danger and be prepared to respond. There is a risk of flooding in low-lying areas whether it is quickly or slowly.

You need to know where to find the latest weather information. It is always better to wait for the water to go down or return to a safer route if you are outdoors. Don't try to get across it. Flood waters can be more dangerous than they look.

Building for a wetter future

Engineers work to limit the damage that rain can do. Water is often directed underneath roads and railways so that people and goods can continue to move safely. After flooding has stopped, water can be held in containment ponds and basins.

Green infrastructure systems, such as rain gardens and green roofs, are being used to reduce flash flooding. Wetlands are restored along rivers and streams.

The design standards and rules that we use to engineer these features are often based on the location where we work. Engineers use that information to calculate the size of a culvert or pond. Excess capacity is always built to handle large floods.

Many parts of the U.S. are experiencing more intense storm events that cause a lot of rain in a short period of time. The recent floods in Kentucky and St. Louis were both on a scale that would be expected to happen once in 1,000 years.

With climate change planners and engineers will need to rethink how to design and manage infrastructure in the future It is difficult to predict how many storms will occur at a given location. When there are other demands for funding, it is not cost effective to design and build for the worst-case scenario.

Engineers, hydrologists and others are trying to understand how to plan for the future so that we can help communities make themselves more resilient. Updating data and design standards will be required.

The conversation published this article. The original article is worth a read.