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Floodwalls Similar to levees, flood walls also keep water away from the building. However, floodwalls are con- structed of stronger materials, are thinner, take less space, and generally require less maintenance than levees. Floodwalls can be constructed using a variety of designs and materials. By taking into account the individual building design, siting, and topography, and with some imagination, a floodwall can be constructed that not only protects a building, but also enhances its appearance. Selection of a floodwall design is primarily dependent on the type of flooding expected at the building site. Tremendous forces can be created by high flood levels and flood velocities. Fast moving water can also be a danger since erosion might undermine the floodwall or its footing and cause a failure, therefore. riprap may be needed to prevent this problem. Closures Closures must be provided for sidewalks, driveways, and other openings left in a flood wall or levee. However, floodwalls and levees designed without closures are normally more effective because there is no need for human intervention. In the case of a levee, access may be provided simply by constructing the levee with gentler side slopes at the driveway to allow vehicles to enter and exit by passing over the levee. When constructing a floodwall or levee around a building, a sump pump must be incorporated to provide proper interior drainage from groundwater seepage and rainwater from the building side of the protection. Closures act to close the openings in floodwalls and levees and prevent water from entering. They can be of a variety of shapes, sizes, and materials. In some cases closures are permanently attached using hinges so that they can remain open when there is no flood threat. They may also be portable, normally stored in a convenient location and slipped into place when a flood threatens. There are a number of elements involved in designing and using a closure system. Closures may be separated into two basic categories: permanent or temporary. Combinations of permanent and temporary closures are also fea- sible. Closures can be considered as an option only if a flooding situation provides sufficient warning time to properly install them. The need for both sufficient warning time and "human intervention" is critical, since all temporary closure systems require personnel to install them and make certain they are properly sealed. Closures that are stored between floods must be readily accessible. The effectiveness of an entire system will be compromised if the closures are stored such that flooding renders them inaccessible, or if even one closure is improperly installed. Closure systems are most effective where there are a limited number of openings. If there are too many, leakage could overwhelm and defeat the system. Any sewers or drain pipes passing through or under a floodwall or levee will require closure valves to prevent backup and flooding inside the building and protected area. 8 DRY FLOOD PROOFI",G Dry flood proofing involves sealing building walls with waterproofing compounds. imper- meable sheeting, or other materials and using shields for covering and protecting openings from floodwaters. In areas of shallow, low velocity flooding, shields can be used on doors, windows. vents, and other building openings. The first step with the use of shields placed directly on buildings is to be certain that both the shield and the building are strong enough and sufficiently wa- tertight to withstand flood forces. Sewer lines should be fitted with cutoff or check valves that close when flood waters rise in the sewer. to prevent backup and flooding inside the building. 11