What Causes Floods? Top 8 Common Causes of Flooding

Flooded yard

Flooding is experienced all over the globe and for a variety of reasons — but why exactly does flooding occur? There are several human causes of flooding, including poorly designed infrastructure. There are also natural reasons flooding happens.

Here are eight of the most common causes of flooding, both natural and human-induced:

1. Heavy Rains

The simplest explanation for flooding is heavy rains. No matter where you live, you are surrounded by infrastructure and systems designed to move rainwater into appropriate basins and reservoirs. In most cases, the infrastructure does its job, and you never have to think about where the rain goes when it runs off.

When it rains heavily, however, those systems are overwhelmed, and that water doesn’t drain nearly as quickly as it needs to. In short, the drainage systems back up, and the water rises — sometimes into homes. This typically happens only in cases of sustained heavy rains over a long period.

2. Overflowing Rivers

You do not necessarily need to have heavy rains to experience flooding in your area. For example, if you live along a river and areas upstream from you experience heavy rains, it could lead to a serious overflow where you live. Most larger rivers include a series of dams to help manage large amounts of rainfall, and most river systems are managed by government authorities.

Sometimes, however, those authorities have to make tough decisions about how to operate dams. They often can manage the water and prevent flooding altogether — but not always.

3. Broken Dams

Much of America’s infrastructure was built in the 20th century, so it is getting old. When heavy rains come, and water levels rise, aging dams can fail and unleash torrents of water on unsuspecting households.

This is part of what happened after Hurricane Katrina hit New Orleans in 2005. Levees failed and made the flooding far worse than it would have been otherwise. While we have come to depend on 20th-century architecture, and much of it does its job well, there is always a possibility that a structure will fail.

4. Urban Drainage Basins

Many of our cities are made of mostly concrete and other impermeable material. When you have an urban drainage basin that is made of concrete, there is no ground for water to sink into. So, when those drainage basins fill up, it is going to mean flooding for low-lying areas.

This is mostly the case in large urban areas — think Houston and Los Angeles. When heavy rains strike, the basins used to drain them cannot always handle the load.

5. Storm Surges and Tsunamis

Rain is not always the culprit when it comes to flooding. Storm surges related to hurricanes and other storms can lead to significant flooding, as can tsunamis that are sometimes caused by underwater earthquakes.

Given modern technology, we often know about storm surges and tsunamis before they arrive, but this is not always the case. For example, in 2004, an earthquake off the coast of Indonesia created a tsunami that gave little warning before coming ashore.

6. Channels with Steep Sides

Flooding often occurs when there is fast runoff into lakes, rivers and other reservoirs. This is often the case with rivers and other channels that feature steep sides. It is a similar issue to having a lack of vegetation, which is explained in more detail below.

7. A Lack of Vegetation

Vegetation can help slow runoff and prevent flooding. When there is a lack of vegetation, however, there is little to stop water from running off. This can be a bit of a conundrum after a drought.

While area residents likely welcome the rain, the lack of vegetation after the drought can cause flash flooding. This does not always happen given that basins and reservoirs are close to empty, but it can occur in cases of extreme rains following long periods of drought.

8. Melting Snow and Ice

A winter of heavy snow and other precipitation can lead to a spring of flooding. After all, that snow and ice have to go somewhere when they melt. Most mountainous areas experience relatively consistent snowfall totals from year to year, but an unusually heavy winter of precipitation can spell bad news for low-lying areas around the mountains when spring hits.

The good news is that sustained winter precipitation provides a long lead time to prepare for potential flooding. That is a silver lining at the very least.

These are just a few examples of common causes of floods, but there does not need to be an incredible weather event for you to experience flooding at your home. You can experience devastating flooding simply due to a clogged or broken pipe as well as other plumbing issues. No matter how or why you experience a flood, you need a qualified water restoration professional with quality tools to help you get your home back into working order again.