Conduct Flood Risk Assessments Effectively

What Is a Flood Risk Assessment?

According to the World Health Organization, it indicates that between 1998 – 2017, floods negatively impacted more than 2 billion individuals all over the globe. On top of this, over 80% of the recorded natural disasters in the last 10 years were because of floods, storms, and drought. A testament to the widespread devastation that results in massive loss of life and damage to property, flooding is one of the most dangerous natural disasters around the globe affecting homes, communities, businesses, and local governments. Individuals who live in floodplains, non-resistant buildings, or those who have no warning systems and flood awareness are especially vulnerable to floods.

This is why flood risk assessments are done, so relevant authorities, engineers, surveyors, architects, and even homeowners understand how likely it is for a flood with damaging intensity to happen at a specific area and its surrounding areas over a while.

A flood risk assessment (FRA) is a document that lists all the potential flood risks to a development site. It seeks to quantitatively evaluate the hazards associated with flood scenarios, their impact on inhabitants, and the economic activity of the area. It should also include suggestions for the implementation of relevant safety measures to reduce the impact of flooding on the area.

Overall, the main objectives of a flood risk assessment are to evaluate whether:

• A project or development could be exposed to flood hazards, present or future, from any source.
• The flood hazards in the area will increase the risk elsewhere.
• The proposed control measures are enough and appropriate to reduce the risks.
• A project or development will be safe for habitation presently and in the future.

This article covers the following topics:

1. Why is it important to consider the flood zone

2. What are the methods for assessing flood risks

3. How does digital application support flooding risk assessment?

Why Is It Important to Consider the Flood Zone?

Before purchasing or developing a home, you must understand the flood risk of the area you’re developing in. One important reason to have your property assessed is for flood insurance. Flood maps show the community’s risk of flooding and can be used to determine flood insurance requirements and costs.

The National Flood Insurance Program (NFIP) reports that over 40% of insurance claims between 2015 to 2019 came from areas mapped outside of high-risk flood zones. This is why it’s important to have your property assessed — so you can take measures to protect it from flood risks.

The reality is, all developments can benefit from flood risk assessments because no one is fully safe from flooding. Whether it’s from a nearby body of water or a storm, any area can experience a flood. Taking necessary precautions can help ensure the protection of lives and properties in the long haul, especially because the Federal Emergency Management Agency (FEMA) reports an area’s flood risk can change because of climate change, land development, and erosion.

To get a better understanding of the flood zone, we refer to FEMA’s classifications. The designated flood zones are moderate- to low-risk, high-risk areas, and undetermined areas. These flood designations are further segregated into two categories:

• Special Flood Hazard Areas (SFHAs): This category includes all zones that are considered high-risk and start with the letters A or V. These areas have a 25% chance of flooding within a 30-year mortgage.
• Non-Special Flood Hazard Areas: This category includes all areas that fall under moderate- to low-risk and starts with the letters B, C, or X. These areas fall within the limits of 100-year to 500-year floods and are eligible to receive one-third of federal disaster assistance from flooding.

To know your area’s flood risk, you can use FEMA’s Flood Map Service Center and search for your location on their database.

What Are the Methods for Assessing Flood Risks?

The goal of the assessment is to evaluate the magnitude of potential flooding that can occur as well as the potential economic loss that it can bring. So, the key factor to making informed decisions on risk management and protection is an accurate flooding risk assessment report.

A flooding risk assessment measures four main things:

• Flood hazards: What is the probability and magnitude of the flooding?
• Exposure: What are the economic value of the properties and assets exposed to flood hazards?
• Vulnerability: What is the relationship of flood hazard properties to the potential economic loss?
• Performance: How effective are flood protection and damage control measures set in place to decrease the impact of flood hazards on exposure and vulnerability?

The methodology for completing a flood risk assessment involves three essential stages:

Stage 1: Flood Mapping and Planning

Once the flood zone of your area has been identified, the planning and initial assessment begin. This is where a comprehensive flood map of the development site will be made and the areas at risk for flooding will be focused on. It will also include a review of previous floods that have happened in the past and an assessment of potential floods that can take place in the future.

Stage 2: Identifying Sources of Flood Risks

The most important reason for performing a flood risk assessment is to find out the vulnerability level of the development site from any future flood hazards, whether natural or artificial.

The assessment typically looks out for eight major sources of flood risks:

• Fluvial: Commonly known as river flooding. This happens when the water level in a river or stream rises and overflows into the mainland.
• Coastal: This normally happens during extreme weather conditions such as storms that cause a rise in seawater levels.
• Canals: Although it’s rare for canals to flood, it can happen when the maintaining structure fails or when a nearby body of water floods into it.
• Groundwater: This usually happens after long periods of heavy rainfall the water level rises beyond ground elevation.
• Reservoirs and bodies of water: The main function of reservoirs and large bodies of water is to retain water in case of flooding. However, when these overflow the water can flow down to floodplains.
• Pluvial Floods: Considered as the invisible flood hazard, it can happen in any location — even those with no bodies of water. They happen when drainage systems are overwhelmed or when heavy rainfall causes flash floods.
• Sewers: Happens when sewers flood due to excessive flows of water or experience blockage in the infrastructure.
• Wider catchment development: Though catchments or watersheds are originally meant to collect rainwater. However, in times of great rainfall intensity the water can cause runoff into sewer networks.

Stage 3: Flood Risk Mitigation

The last stage of an FRA is focused on establishing safety measures and damage mitigation to reduce the risks of flooding to acceptable levels. This will include recommendations to install flood defenses to control the potential damage to assets, manage residual risks, and even improve existing water systems.