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Building to Minimize Risks

Flood Hazards Can Mean Changes in Construction, Renovation, and Mitigation


Natural disasters have made headlines all across the country in the past few years. El Nino has spawned floods, landslides, severe winter storms, and tornadoes. Other notable events include the Red River of the North, the Great MidWest Floods, the Northridge Earthquake, the Winter Storm of the Century, the Great Northeast Freeze, and dozens of hurricanes such as Andrew, Hugo, Alberto, Iniki, and Fran.

The number and severity of disasters seems to be increasing, and more and more people are building and living in risky areas. Since 1964, more than 1,200 disasters have been declared by the President of the United States. Every state has been hit, but some states are more vulnerable than others (see map on page 59).

As with any problem, it is better to know what you're facing and to learn how to respond and how to minimize the risks. Finding out today about hazards you may experience in the future will help you to protect your property and residents.

Flood hazards have been identified in every county in every state, and in more than 18,000 cities and towns. Coastal communities are vulnerable to surges of water caused by hurricanes, tropical storms, nor'easters, tsunamis, and prolonged on-shore winds. Inland communities are vulnerable to cloud bursts which swell small creeks and streams, and large rain storms which overflow the banks of larger rivers.

People who build and live close to the water often recognize that flood risks are likely. But sometimes it is hard to understand that a placid stream may become a rushing threat. Sometimes property that is far from the water is still vulnerable to flood damage. In the Great Mid-West Floods, the Mississippi River and other waterways spread over miles of adjacent land. In low lying areas along the coast, tidal surges may push inland for more than 10 miles.


In 1968, Congress created the National Flood Insurance Program (NFIP). Administered by the Federal Emergency Management Agency (FEMA), the NFIP provides flood insurance which is not available from private insurance companies. The NFIP also develops flood hazard information in the form of Flood Insurance Rate Maps (see figure on page 60). These maps are kept in your local planning or building permit office and are available for inspection. This is the best way to find out if your property is at risk of flooding.

Check with your property insurance agent for flood insurance. Your regular property insurance does not include flood damage.Your agent can place a separate policy, which is available from the National Flood Insurance Program. It is important to understand what is and is not covered by federal flood insurance. Of particular significance is that enclosed areas below ground level, including basements, have very limited coverage.

Even if a floodplain building has not suffered damage in the past, protection measures may be required if substantial improvements and renovation work are planned. As part of the NFIP, communities are required to issue permits for such improvements. Mitigation measures such as those described in this article may be required to protect against flood damage. Check with your engineer and local building permit office for specific requirements.

The best mitigation measures are applied before a flood-prone building is constructed. Communities that participate in the National Flood Insurance Program are required to determine when a new building is proposed to be located in a mapped floodplain. Ideally, new buildings will be located on high ground or set back from the water in order to minimize exposure. In some areas, good planning helps preserve floodplains to serve their natural functions.

With the help of a community official or an engineer, you can learn how deep flood waters are expected to be for the '1 percent annual chance flood.' This flood has a 1 in 100 chance of occurring in any year, and is often referred to as the '100-year flood.' While that may not sound like a great risk, such floods happen in communities all across the country every year. Plus, most floods that cause damage are not the big ones that make the headlines. Smaller floods can and do happen frequently, and some flood-prone buildings have been damaged 10 or more times in past 20 years.

After you learn how deep and how frequently flood waters are expected to occur, you can explore your protection options. In cases where very shallow flooding is expected very infrequently, doing nothing may be a reasonable course of action. But that usually is not the case, especially if your investment is high or if residents could be endangered.

Find out about local flood conditions, flood warnings, and evacuation procedures. Check with your local emergency management office to find out about local flood response plans. Where sufficient advance warning can be made, local officials may have developed procedures to notify at-risk properties, especially those with high populations.

Some states and communities require owners of apartment buildings in flood-prone areas to include a notice of flood risk in leasing information. Even if local laws do not require this notice, it may be valuable to limit liability. It is also important for public safety and to encourage renters to obtain flood insurance for their contents. Regular renters insurance does not provide coverage for flood damage.

If you have determined that your apartment property is in a flood-prone area, and after you have purchased flood insurance, you are ready to evaluate measures to protect against damage. Some information on simple property protection measures, including post-flood cleanup, is available on FEMA's Internet Web page at Your local planning department or city engineer's office may also have some resources.

But floods usually do more than just get things wet. When flood depths exceed one to two feet, and especially when strong currents or waves are likely, sometimes walls collapse and foundations are undermined. It is best to get an experienced professional engineer to help evaluate protection options. You should also check with your community, because some mitigation measures require a building permit.

Some mitigation options may be simple and low cost. For example, if a basement utility room floods frequently, the easiest measure may be to relocate the mechanical equipment above anticipated flood levels. In some cases, window openings through which water enters a building may be blocked. However, care must be taken because water pressures may build up and cause structural damage.

When an apartment building is subject to flood waters that are several feet deep, more complex mitigation measures may be required. If several hours of warning are available, a structural floodwall with special door closures may be feasible. Such measures, called dry floodproofing, may be appropriate to protect non-residential areas, such as utility rooms, laundry or storage space, activity rooms, and building access areas. In some cases, if designed by an engineer and permitted by the community, a small earthen berm may be constructed around one or more buildings. Permitting is required because berms may push more water onto adjacent properties.

Sometimes, however, there are no feasible options to keep water out of a building. In these cases, cost effective measures may involve allowing water to enter so that expensive structural damage is avoided. This approach, called wet floodproofing, involves changing how flood-prone space is used, relocating or elevating equipment such as water heaters on platforms, and replacing finished wall and floor coverings with water resistant materials.


In this era of growing flood hazard awareness, property owners may find that there is financial assistance available from a number of sources. After major flood disasters, FEMA and other federal agencies provide funding for mitigation projects. The funds, often administered through the state and community, are intended to support cost-effective mitigation measures. Some housing agencies may fund mitigation projects that protect low-to-moderate income housing, especially in areas where such housing is scarce.

One example of an early mitigation success took place in Baltimore, Maryland, in the mid-1980s. A multi-story building with garden apartments had flooded several times in less than a decade. Due to the depth and frequency of flooding, engineers determined that the most feasible measure involved eliminating the below-grade units. The units were filled with gravel, capped with concrete, and designed so that flood waters drained freely to reduce moisture problems. To make the project work, the city purchased the rights to the apartments, supported in part by state funding. The project not only prevented flood damage, but reduced risks to residents and city rescue personnel.

If your property is located in a high 'risk earthquake area or if your community is subject to high winds, you should check with your engineer or building code official. There is a wealth of techniques to reduce damage from all natural hazards, and such mitigation measures should be considered to protect both people and property.

Quinn is mitigation program manager for Michael Baker, Jr., Inc., a multi-disciplinary engineering firm in Annapolis, Maryland.
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Author:Quinn, Rebecca
Geographic Code:1USA
Date:Jun 1, 1998
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