Flooding is a natural occurrence that happens when heavy rain falls on Earth and fills up depressions, low-lying areas, and other surfaces that typically remain dry. It is a natural part of the water cycle and happens almost everywhere on our planet. Despite the bad press it receives, flooding serves an ecological purpose and therefore has several environmental benefits. 

Benefits of flooding

  • Recharges groundwater
  • Creates temporary wildlife habitat
  • Increases fish production
  • Recharges wetlands
  • Rejuvenates soil fertility for agriculture
  • Constructs floodplains

While flooding has several environmental benefits, it becomes a problem when it causes damage to human settlements. Because humans have built on floodplains and other flood-prone areas, we have put our infrastructure at increased risk. Building dams, drains, pipes, and other infrastructure to convey water either toward or away from cities has altered the natural water cycle, and in return altered natural flood patterns, leading to increased flood severity. 

Flooding accounts for approximately one-third of all natural disasters and affects more people than any other natural disaster (Talbot et al). There are many risks associated with flooding because it is so widespread. Floods can have immediate and long-lasting impacts, jeopardizing economic, environmental, and human health. 

Risks of flooding

  • Dangerous landslides
  • Loss of crops and livestock
  • Disruption of normal drainage systems
  • Water pollution through spillage of raw sewage and animal waste
  • Accelerated discharge of industrial and urban and toxic materials 
  • Damage to homes and other infrastructure 

Flooding across the globe

Flash flooding on May 21, 2024 swept away cars in a dealership in Omaha, Nebraska. Image source: KETV Omaha
Heavy flash floods have wiped out several homes after a dam collapsed in Mai Mahiu, Kenya on April 29, 2024. 71 people have been confirmed dead and 110 are hospitalized. Image source: CNN
Historic flooding in Rio Grande do Sul, Brazil has submerged homes, caused landslides, and collapsed bridges. Over 800,000 people are believed to be without water, 100 people are missing, and 75 people have been confirmed dead. According to the Brazilian Geological Service, water levels are the highest they’ve been in 150 years in some cities. Image source: Sky News

Flooding in central Indiana 

Already this year central Indiana has been subject to several flood warnings, prompting many travel warnings and in some cases making roads impassable. A flood warning issued on April 11 lead to several road closures across the city. Four people and their pets had to be rescued by the fire department after becoming trapped in high water on Indy’s southwest side. 

Indianapolis fire crews rescuing people and animals stranded by flooding. Image source: WRTV 
Flooded road in Indianapolis. Image source: IndyStar

Another flood warning was issued more recently on May 15, causing flooded roads, submerged cars, and multiple crashes.

Submerged car as a result of the flooding in central Indiana. Image source: WTWO Terre Haute
The sandbar of Flowing Well Park is completely submerged after flooding on April 2, 2024. Image source: Susie McGovern

Back in September 2022, one woman was killed in southern Indiana as flash flooding destroyed homes, vehicles, and uprooted trees.

Excessive rainfall is one of the major drivers of flooding, a trend that experts say we can expect to see continue in the future as we battle the effects of climate change and other land-disturbing activities. 

According to Purdue University researchers, rainfall is projected to increase over the years, particularly in the winter and spring. In fact, Indiana has already been experiencing an increase in precipitation, which has led to higher-than-average streamflow. A 30-year study revealed that 98 out of 109 streamflow gauges across the state reported an increase in streamflow, with central Indiana seeing a disproportionate amount of rising streamflow (Purdue University).  

Annual average streamflow trend for the past 30 years for each USGS streamflow gauging station in the state. Image and caption source: Purdue University

Flood Types

Floods can be categorized by the time it takes to flood or by the area experiencing flooding. Below are some examples of the common flood types that researchers use to characterize extreme weather. 

  • River floods happens when water levels exceed the capacity of a riverbank, causing water to spill over the top.  
  • Coastal floods are the result of higher than average high tides, often coupled with heavy rainfall and winds. 
  • Urban floods are floods that occur in cities and other built-up environments, when man-made drainage systems cannot keep up with rainfall. 
  • Flash floods occur when intense rain falls over a short period of time, typically less than 6 hours.

How can we minimize the risk of flooding?

Flooding is going to happen regardless of how many dams, flood walls, and flood resilient structures we build because flooding is part of the water cycle. Minimizing the risk of flooding is to protect humans from the economic, environmental, and health related risks of flooding. Flood related disasters are costly and can take a long time to recover from, so it is important to understand how to mitigate the risks and costs associated with flooding. 

  • Avoiding alternation of and development near rivers, wetlands, and floodplains.

In addition to climate change and rising global temperatures, flooding is exacerbated by human development. Changes in land use that require drainage networks to move water off site increase the severity of flooding by increasing the amount of water that is conveyed to nearby rivers and streams. This limits the capacity of our natural systems, and in return, causes flooding. 

Building on flood-prone areas and alternating natural drainage networks also increases the risk of flooding by putting structures directly into harm’s way. For example, the construction of bridges, which encroach onto a river’s floodplain, can increase upstream flooding by narrowing the width of the channel, increasing water flow resistance, and creating a large backwater upstream (United States Geological Survey).

  • Installing green infrastructure. 

In cases where development on flood-prone areas is not avoided or the use of gray infrastructure is proposed, green infrastructure is a viable option for flood reduction, especially for the cost savings benefits. Green infrastructure (GI) refers to natural or man-made drainage networks that mimic nature, as opposed to gray infrastructure which refers to drainage networks like pipes, culverts, and drains. Forests, wetlands, rain gardens, bioswales, green roofs, and permeable pavement are all examples of GI.

The Capital Region Watershed District in Minnesota conducted a study on GI for flood prevention and found that installing GI, at an estimated cost of $2 million, was more cost effective than installing an all-gray infrastructure alternative, at an estimated cost of $2.5 million (Environmental Protection Agency). 

The City of Goshen, Indiana completed a flood resilience plan which recognizes the importance of GI in the planning and design of the city. The plan lays out goals related to the adoption of GI to improve flood resilience, such as training staff about GI practices and customizing the city’s stormwater ordinance to include requirements for GI. 

  • Protecting wetlands and other natural areas. 

Wetlands are areas where water is temporarily or permanently stored and are one of our best protective measures against flooding. Just one acre of wetlands can store up to one million gallons of water (Environmental Protection Agency). One study demonstrated that restoring the 100 year flood zone of the Upper Mississippi watershed could store 39 million acre-feet of floodwater, the volume of water the caused the Great Flood of 1993, and save over $16 billion in projected damage costs (Environmental Protection Agency). 

The removal of vegetation and natural areas increases flood risk. Imagine a plot of land 100 percent covered with a wetland, plants, and trees. Water will be absorbed by the wetland, both in the soil and on the surface. The plants and trees will uptake water into their leaves, stems, and root systems, storing it for essential processes like photosynthesis. Up to 95 percent of a plant is water, making them an essential and overlooked component in water storage. 

Now imagine a plot of land that is 80 percent concrete and buildings, and 20 percent plants and trees. Much of the water that was being absorbed by the wetlands, plants, and trees is now hitting the surface of the buildings, parking lots, and other paved surfaces, flowing down gutters and towards drainage networks that convey water rapidly to a nearby river of stream. 

The example given above is for illustration purposes only and is not intended to reflect any scientific study. When development occurs on natural areas, it essentially reduces the capacity of the land to store water, and in return, that water goes somewhere else in the watershed – most often to rivers, streams, or retention ponds. As development accelerates, we not only continue to lose the natural water storage systems, but at the same time we strain the already existing ones. Therefore, protecting wetlands and natural areas from development is essential to minimize flood risk.

Swamp wetland at Ritchey Woods Nature Preserve in Fishers, Indiana. Image source: Susie McGovern