Reducing Riverine Flood Risks

 

Floods are the most common natural disaster in the United States. We tend to think that floods happen mainly around coastlines and during hurricanes, but America is experiencing more frequent and devastating floods along creeks and rivers, lakes and ponds, and areas with inadequate drainage systems. In some cases, extreme precipitation events such as atmospheric rivers, in-land tornados, and melting snow/ice can also cause floods in unexpected locations.

Texas, New Orleans, and Florida are known for their massive flooding experiences following hurricanes. Yet, many other regions in the U.S experienced severe flooding throughout the years. Massive floods have occurred along the Mississippi river hitting communities from Illinois to Louisiana. States such as South Dakota, West Virginia, Oregon experienced flash floods from heavy rains.

Historic floods left behind life casualties, broken families, and displaced communities. While many lessons have been learned and many solutions have been implemented, recent events imply the future is lining up bigger challenges.

Preparing for future floods can help avoid loss of property, injury, and death. Beyond preventing direct damage from flood water, we can also prevent life disruptions from flood events, such as prolonged outages, risk zones of mud and landslides, broken supply chains of food and water, and limited transportation.

In this blog we cover the following key strategies which may help protect your home from flood damage:

• Elevation of the home above BFE
• Designing according to your climate zone
• Adoption of Water Resistive Materials
• Building Rain Gardens 
• Elevating Essential Infrastructure
• Backing up Critical Systems
• Flood vents
• Flood barriers
• Government funds/grants to mitigate risks
• Flood Insurance

 

Many states and local municipalities in the U.S share flood maps that determine which locations are flood-prone. Many also have granular data on risks as well as corresponding building codes. 

The Federal Emergency Management Agency (FEMA) has a Flood Map Service Center (MSC) which is an official public source for flood hazard information that includes flood maps, flood hazard products, and tools for better understanding flood risk.

There are many ways to deal with floods, from simply securing your valuables at the most elevated spot in your house to elevating the entire house above the Base Flood Elevation (BFE) level. 

The best way to properly design and build your house to protect it from excess precipitation and floods is to consult with an expert on local risks and building codes. 

Yet, we list the main strategies that can be used for both new construction and existing buildings. Feel free to use the Glossary of Terms if there is a term we neglected to explain.

 

Elevation

A familiar flood mitigation measure is elevating a property above the Base Flood Elevation (BFE) or relocating it to higher ground outside of a high-risk flood area. BFE level is the height to which floodwater is expected to rise during the base flood—a flood of that magnitude has a one percent chance of occurring in any given year. 

It would be wise to avoid building in flood-prone areas. If this is not possible, the building should be raised above ground level to minimize damage in the event of flooding. The flood zone levels to which the building should be raised is above the BFE of the location. FEMA provides an interactive map that can help find the BFE by address. 

 

Design according to your climate

Properly design your house (foundation, walls, roof) to allow interior and exterior surfaces to dry. The flood zone house designs should adhere to the climate zone you are in, the temperatures inside and outside the house, and the humidity. These will determine the insulation, and the airtightness applied. Allowing vapor, precipitation, melting snow, and ice to dry quickly will prevent risks of health issues, damage, and extra cost. 

Consult with knowledgeable professionals and make sure they walk you through the design and material choices available and how the house system will behave during your climate zone’s normal conditions and during and after extreme events such as floods.

 

Water Resistive Materials

The main concept here is to take advantage of building materials that can dry relatively quickly, resulting in minimal damage and preventing decay and mold issues. This strategy is helpful, especially in locations where there is a higher risk of flooding or hurricane damage.

Examples of water resistant materials are preservative-treated wood framing (environmentally friendly treatments like borate), fiberglass-faced rather than paper-faced drywall, and tile or resilient flooring rather than carpeting. In addition, newer materials such as fiber cement products, and certain types of metals also resist water damage.

There are eco-friendly options that we encourage exploring, here are some to get inspired by:

• Preservative-treated wood - its key benefit is resistance to water, fungal, and insect damage. Not only will it improve the resilience of your house, but it will also contribute to the environment because it requires less maintenance and provides longevity that eliminates further forest harvesting. For years, wood was treated with chromated copper arsenate (CCA). In 2004 the U.S Environmental Protection Agency (EPA) reached an agreement to end the sale of CCA-treated wood for most wood-based products due to its toxic nature. Today, most common wood products are treated with ACQ as an alternative. However, even ACQ is considered to have risks with its copper substance. Borate-based treatments, among others, are considered safer. However, you should consult with an expert to properly match the wood to your environment as different treatments behave differently in various climate zones.
• Fiberglass-faced drywall - while paper-faced drywalls are more common and affordable, they pose a risk in humid and wet areas as they tend to develop mold. Using mold-resistant drywall may be more expensive upfront but will provide longevity and resilience.
• Fiber cement - while wood is probably the most pervasive material used for sidings, today you can find various types of sidings such as aluminum, vinyl, stone, brick, stucco, or fiber cement. The latter is considered an eco-friendly alternative, however, it requires an expert to manage the installations, ongoing treatment, and upfront costs are higher. Make sure that your choice of wood alternatives for sidings matches your climate zone and usage objectives within your built environment.
• Resilient flooring -  in flood-prone zones consider avoiding carpet flooring and even wood. Instead, use more durable, water-resistant solutions. Popular solutions that fall under the green category would be vinyl, linoleum, cork, and rubber. When looking at both green and resilient, it is advised to focus on linoleum solutions made of 100% natural substances (versus vinyl and rubber which in many cases use gas-emitting chemicals). Consult with an expert regarding the materials used to install the floor (e.g. glue) and make sure those are also resilient and safe.

In many cases, flood resistive materials are the “go-to” solution when more expensive and complex solutions are not feasible (such as elevating the house above the Base Flood Elevation level (BFE) as mentioned above)

 

Rain Gardens

Rain gardens are a great landscape solution against water runoff and a way to help our community as well as our own water quality. A rain garden is a garden of native plants located in the lower area of your yard. You can observe where rainwater in the yard flows after massive rain, and plan your rain garden in that location. By digging a ditch or creating a small barrier/slope, and planting the right plants, you can help stop excess rainwater from running off and ending up overwhelming the local sewer system or water reservoirs. According to the Groundwater Foundation, “rain gardens are effective in removing up to 90% of nutrients and chemicals and up to 80% of sediments from the rainwater runoff. Compared to a conventional lawn, rain gardens allow for 30% more water to soak into the ground. Rain gardens will drain within 12-48 hours, thus preventing the breeding of mosquitoes.” You can read more on the effects of stormwater runoff here. 

New Orleans has dedicated a section in their NOLA-Ready website to green infrastructure. It is a highly recommended “go-to” website in general. Specifically, the green infrastructure section mentions several strategies to develop a flood resilient community, each strategy includes an explanation, the amount of effort/labor, cost, and efficacy.

The strategies mentioned are:

• Rain Garden
• Detention Basin
• Stormwater Planter Box
• Infiltration Trench
• Pervious Pavers
• Rain Barrel
• Plant Trees

 

Elevated Essential Infrastructure:

Essential infrastructure systems including HVAC, fuel supply, electrical systems, and appliances should be protected from floodwater and storm surges. In addition to water damage, the pressure exerted from moving floodwater and storm surges and the dissolved chemicals, silt, suspended solids, and floating debris that are often carried with flood water can damage them as well.

To limit the effects of flooding and storm surges on building support systems, it is recommended to elevate them above the projected water elevation.

FEMA’s P-348 2nd edition from 2017 is a comprehensive guide for professionals that covers principles and practices for the “Design and Construction of Flood Resistant Building Utility Systems”. This guide can help protect your utilities and equip yourself with ideas and knowledge on flood protection when building or retrofitting your house.

 

Backing up Critical Systems

Resilience strategies aim to either prevent damage to a building’s equipment in the event of a flood or storm surge or to provide backup and redundancy for running critical systems.

This strategy helps maintain critical building functions in the event of a power outage or water supply loss.

The maintenance and operation of critical systems in the event of a power outage should be prioritized in the design of the building as well as in the operations and maintenance plans.

Critical systems should be backed up with renewable power generation, a generator, or a battery backup system. A building that has backup power generation is more resilient than a comparable building without those systems.

As for water supply backup, there are numerous emergency backup water systems that can be installed in the house, from basic water storage tanks to more sophisticated solutions that rotate the water for you. A couple of examples are Constant Water and ReadyMadeWater.

 

Sewage backflow protection

Floods can inundate and overload sanitary and rain sewer systems. As a result, water can flow backward through sewer lines and out through toilets or drains. There are several backflow prevention solutions, however, please note that installation of backflow valves and other plumbing modifications may be regulated by your state and local building codes, therefore it is highly advised to consult with a licensed plumber or contractor regarding your options.

 

Flood Vents

In general, we want to prevent water from entering our properties. Yet, trying to keep out water in an event of severe flood with high water pressure, may break and destroy walls and foundations. Instead, we can manage the flood water to enter and exit the property quickly causing as little damage as possible. This can be done by installing flood vents in enclosures below the Base Flood Elevation (BFE). This is also called Wet Floodproofing. Make sure to install engineered flood vents that are designed to operate only when needed. 

 

Flood barriers

You can place or install residential flood protection solutions such as aluminum flood shield barriers that can be mounted on doors or windows, or biodegradable sandbags, to protect from flood water entering the property. Note that these solutions protect from floods that do not exceed the height of the barriers installed. 

Unfortunately, we couldn’t find third-party certified products or environmentally friendly manufacturers. If you know of such, please contact us. 

 

Financial assistance for risk mitigation

Both FEMA and local governments plan and issue funds to carry out hazard mitigation projects. Hazard mitigation investments are “pre-disaster” that aims to build the resilience of communities and homes as preparation for future events.

Eligibility for most grants is at the local government/community level but homeowners/individuals may apply through their community. First, check with your local representatives if your county is eligible for funding and if so, ask your community representatives to apply on your behalf.

Here is the starting point with FEMA’s HMGP- Hazard Mitigation Grant Program.

 

Flood Insurance

Most insurance companies exclude flood damages from their homeowners’ insurance coverage.

However, flood insurance can be purchased separately. The National Flood Insurance Program (NFIP) provides flood insurance to property owners, renters, and businesses, to assist with a fast recovery when floodwaters recede.

The NFIP insurance is mandatory in Special Flood Hazard Area (SFHA). If your property is located in a high-risk flood area and your mortgage lender is federally regulated or insured, the lender is mandated to require flood insurance. The lender can also decide to require flood insurance even if they are not mandated to.

Note that if your location is not considered SFHA, it doesn’t necessarily mean that the location is not at high risk of a flood. Experts consider FEMA’s flood maps to be outdated and not provide the true flood risk in some areas. 

The NFIP insurance can be purchased from private insurance companies which are also responsible for customer service, but the federal government is responsible for underwriting losses.

NFIP insurance provides two separate policies:

1. For the building itself
2. For the content of the building: personal belongings.

You can decide to purchase one or both.

We looked at flood insurance from Allstate as an example:

Building property coverage includes the physical structure of your home or non-resident property, including electrical and plumbing systems, refrigerators, window blinds, and more. The maximum coverage in this policy is $250,000.

Personal property (contents) coverage includes items inside your home, like clothing, furniture, electrical appliances, valued at the time of loss. This policy’s coverage is limited to $100,000.

Both policies do not cover:

• Damage caused by moisture, mildew, or mold that could have been avoided by the property owner
• Currency, precious metals, and valuable papers like stock certificates
• Property and belongings outside of a building like trees, fences, and swimming pools
• Living expenses like temporary housing.

The rough average cost of flood insurance is $700. The cost differs according to factors such as the location of the property and if it is a high-risk zone, and the age of the property. You can also find calculated premium averages by State.

As of October 1st, 2021, FEMA updated the NFIP pricing methodology for the first time in fifty years. The new methodology is meant to incorporate more flood risk variables such as flood frequency and type, the distance of a property to a water source, and specific property characteristics such as elevation and cost to rebuild. 

Note that flood insurance has a 30 day waiting period after the purchase before the coverage takes effect, so if you decide on purchasing flood insurance, don’t wait till the last minute.

One way to reduce the cost of your flood insurance is to enroll your community in the Community Rating System (CRS) which is an incentive program provided by the NFIP. The city of Livermore received a 20% discount on flood insurance by making their city more flood resilient.

Another way is to retrofit your house to make it more resilient to floods by exercising one of the following strategies:

• Elevating your property, or at least elevating the utilities and HVAC equipment to higher levels if possible.
• Install a sewage water backstop
• Include porous surfaces in your landscape

You can explore mentioned and additional strategies in this document and webpage by FEMA. 

 

Final Thoughts

Floods are the most common natural disaster in the U.S.

Floods traditionally happen in known risk zones however, in recent years, climate change has brought on extreme events which overwhelmed zones that were considered prepared and protected as well as catching communities out of risk zones by surprise.

Planning and executing flood mitigation strategies must be led by local governments and communities working together to carry out citywide planning, infrastructure preparedness, and disaster recovery plans.

However, homeowners should be informed regarding steps they can take to make their homes more resilient to flooding.

Homeowners need to research risk mitigation strategies, either by adopting the latest building codes or in high-risk zones consider looking at strategies that go above the building codes which are considered the minimum.

In this blog we covered at a high level some of the main strategies that homeowners can adopt to better prepare against the risks of floods:

• Elevation of the home above BFE
• Designing according to your climate zone
• Adoption of Water Resistive Materials
• Building Rain Gardens 
• Elevating Essential Infrastructure
• Backing up Critical Systems
• Flood vents
• Flood barriers
• Take advantage of government funds/grants to mitigate risks
• Purchase flood Insurance