Flood Studies: A Brief Introduction

We’ve had a lot of flooding in central North Carolina over the last year. Hurricanes, tropical storms, and even summer thunderstorms have caused local lakes and rivers, such as Lake Jorden and Crabtree Creek, to rise and flood nearby roadways, bridges, and structures. In July of 2025, UNC published a study showing that flooding is more common and widespread in the state than we had previously thought. In the face of this study and the apparent increase of damage, flood preparedness tools can reduce the risk of the loss of property and life. One of the tools that A&O employs is the flood study.

What is a Flood Study

A ruined bridge in a state park

A flood study is an analysis of a stream, river, or lake to learn what the impact of a flood would be. FEMA and other official studies use the 100-year flood, a flood that has a 1% chance of occurring each year, as a standard. This is mostly for insurance or regulatory purposes, and it’s possible to use a 25-year, 500-year or even a 1,000-year flood in a study as well. Using a flood study, it’s possible to learn how deep a projected flood will be, how far it will go past the banks or shore, and even the velocity of the flood waters.

What are they used for?

A damaged section of Hillsborough’s RiverWalk Trail

The primary goal of flood studies is risk prevention. In this vein, the first step in preventing loss of property or life in a flood is to make sure that the buildings are not constructed within a flood hazard zone. While flood studies are often used for insurance, developers and property owners can also have a flood study done so that structures can be built outside of affected areas.

Are they only for buildings?

The eno river suspension bridge with a tree branch brought from floodwaters still attached

Flood studies are just as important for greenways, roadways and bridges. When constructing a roadway or pedestrian bridge over water, a flood study can estimate the likely location and height of floods. This helps us to design and place bridges to span those areas. Roadways and greenways can use them so that people and cars can travel more safely and minimize the risk of flood damage. Dams that affect people or property also require flood studies as part of the EAPs discussed in our other posts. Flood studies are a necessary part of the safety of multiple types of structures.

As we become more aware of the risk of flooding in North Carolina, the need for risk assessment increases. By constructing buildings outside of potential hazard zones, building bridges that span floodplains, and designing roads to avoid dangerously low areas, losses of life and property can be potentially avoided. Even in the case of sudden emergencies or flooding that exceeds the proposed scope, existing prevention measures, such as EAPs, can help to forewarn people most at risk. While we hope that the future brings a decrease in severe storms and the disasters associated with them, A&O hopes to be at the forefront of helping communities understand potential flood risks and developing practical solutions to support them and prepare them for the future.

If you are interested in learning more about our work in bridge design, flood studies, EAPs and inspection services, please visit our project pages.