What is Flood-Proofing?
Flood-proofing is any measure - structural or nonstructural - intended to prevent damage from flooding to a building.
Flood-proofing requires that home owners, builders, architects, engineers and planners, engage in detailed assessment of the feasibility of building in high-risk flood-prone areas.
Besides structural measures, flood-proofing also covers the preparation of plans to initiate standby or emergency measures in anticipation of a flood, such as sandbagging, moving furniture and valuables to high floors, blocking openings or safely evacuating the premises.
Flood-proofing is not a cure for all flood problems. It is just one of the many available flood damage reduction tools.
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Factors to Consider When Flood-Proofing Your Home
Consider the following factors before attempting to flood-proof your home:
- Height of maximum flood level: the lower the depth of floodwaters, the easier it is to flood-proof a building or other structure.
- Velocity of water flow during flood peaks: the lower the flow velocity, the easier it is to design a building resist floodwaters.
- Duration and frequency of floods: the susceptibility to flooding of a given area makes flood-proofing more difficult and expensive.
When floodwaters surround a building they impose uplift (vertical) and lateral (horizontal) loads on the structure and sub-structure. The pressures exerted by these loads must be pre-determined in order to design adequate flood-proofing.
Most commercial and industrial buildings have sufficient anchorage and connections and are massive enough to resist lateral forces produced by floodwaters. In contrast, residential buildings often require special design modifications because they usually have neither the necessary anchorage nor the strength to resist lateral forces.
Uplift and lateral forces against a foundation slab and walls, caused by the infiltration of floodwaters through the foundation backfill, are especially significant in building design and construction.
The decision to use flood-proofing techniques alone, or in combination with flood protection works such as dykes, requires a cost-benefit analysis.
If you are seriously considering adapting any flood damage reduction methods, obtain the services of a qualified professional engineer to help you select and design the right measure tailored to your particular needs.
This is especially important if your house or light-framed structure is, or will be located in an area susceptible to fast-moving flood waters, or the cost involved is substantial.
Remember, flood-proofing measures will not necessarily eliminate the risk of your house ever being flooded. If anticipated benefits exceed the estimated cost then flood-proofing will be economically justified.
Costs will vary considerably, however, depending on local flood characteristics, viz. the type of size of structure; the financial terms of capital to be invested; and the elevation to which the building must be protected, say for insurance purposes. Benefits, therefore, depend on the estimated flood damage that flood-proofing will prevent.
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Basic Flood-Proofing Methods
Flood-proofing techniques usually require either dry measures or wet-flood techniques to secure thorough protection.
- Dry flood-proofing
- Wet flood-proofing
This refers to structural changes or measures applied to those portions of buildings located below the design flood elevation to keep the enclosed space completely or dry during a flood. If done incorrectly, the walls may collapse, causing more damage than if the structure were allowed to flood in the first place.
There are five types of dry flood-proofing:
- Building on fill:
New subdivisions or single buildings are often constructed on fill, raised above the design flood-level. The best filler is sand. Clay, sandy or gravely soil will also work. You will also need heavy plastic sheeting to provide water-proofing. Gradual sloping, good soil and ground cover should minimize erosion.
- Building on piers, piles, columns or bearing walls:
Elevating structures above design flood-levels on some kind of support (e.g. stilts) provides reliable protection against flood damage. This method uses land efficiently, does not raise the flood-level and has minimal adverse effects on flood flows. This alternative requires careful design to prevent damage to supports from floating debris. It also allows sufficient space for flood waters to pass underneath the structure. It cannot be used for large, existing buildings and may be difficult to apply, even to small, light structures.
- Making lower levels of buildings water-tight (closure and seal method):
Flood-proofing the lower levels of buildings by sealing all walls and openings against water penetration, requires that they be made strong enough to withstand cracking from the lateral and uplift pressure of the water. You should obtain the services of a qualified professional engineer to help you select and design the right measure tailored to your particular structure, especially if your house is located in a flood hazard area.
- Surrounding buildings with flood-proof walls or berms:
Walls can be constructed of brick, stone, concrete or other similar materials.
Sandbagging will be appropriate if predicted flood heights will be higher than your levee or other protection. Sandbags can be stockpiled in advance of a flood emergency. You should purchase specially made sandbags; not plastic garbage bags, burlap or some other type that will not hold up.
Wet flood-proofing simply means minimizing damage when floodwaters enter your house. There are five aspects to wet flood-proofing your structure:
- Remove hard to evacuate items that are subject to water damage such as furniture, large appliances, power tools, etc.
- Protect what cannot be moved.
- Relocate or adjust utilities such as electrical outlets, gas appliances.
- Seal off sewer and water systems to prevent health hazards.
- Tape-over heating and air conditioning ducts along the bottom to permit to dram out when floods recede.
- Let water in by ensuring that a doorway, window, or inlet pipe will be open to let outside water in, before it gets deep enough outside to damage your walls.
- Have an evacuation plan that gives you adequate warning time to move valuable items out of the area, especially non-insurable items such as valuable papers, etc.
- Turn off all utilities.
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