Floods | Natural Risks

Flood effects may be limited to a local event affecting an individual community in a low‐lying area or adjacent to a river, or may be widespread, affecting entire river basins. Floods may occur in a matter of minutes (i.e., flash floods), or may develop slowly over a period of days. Flash floods often have a dangerous wall of water that carries rocks, mud, and other debris, can sweep away buildings, vehicles, and other structures in its path, and occur with little sign of the rainfall that initiated the event. Overland flooding occurs outside a defined river or stream, such as when a levee is breached. Overland flood effects can be limited, or can engulf an entire city resulting in catastrophic levels of devastation. Flooding can also occur when a dam breaks, or when water is channeled without warning along small streams, gullies, creeks, culverts, dry streambeds, wadis, or low‐lying ground that might appear harmless in dry weather.

Companies should ensure that weather warnings are tracked and local advisories regarding safe and unsafe areas are identified. Personnel should avoid dry riverbeds, low‐lying areas, and valleys during storms. Upon notification of a flood warning, managers should ensure that all electrical appliances, water, and supplies are moved above ground level. Where possible, water barricades should be constructed using sandbags against doorjambs and cracks, or around buildings and valuable materials. During a flood, personnel should avoid streams, drainage channels, canyons, and other areas known to flood suddenly. If flash flooding is a possibility, personnel should be moved immediately to higher ground or to the top level of a building. Managers should track radio and television broadcasts to stay abreast of the situation, and to listen for local emergency alerts or instructions if caught within a flood‐stricken area. You can post your status and requirements for emergency services using sheets, paint markings, or other indicators as to the number of personnel within a facility, any injuries that require treatment, and special assistance required.

If personnel need to leave a facility, they should not walk through more than six inches of moving water, as the water velocity can cause them to fall. In addition, moving water can disguise holes or hidden obstructions that could result in injury. If movement through water is necessary, still‐water areas should be selected and a stick should be used to check depth, identify holes, or discover underwater obstructions. Individuals or groups being evacuated should be tied to one another on a safety line and should be aware of the threats from power lines and debris hazards. Personnel should not attempt to drive vehicles through a flooded area if the water is higher than the bottom of the door, as such levels will likely cause the vehicle to stall or lose traction. One foot of water will float most vehicles, and two feet of rushing water can carry most vehicles downstream.

Once the initial effects of a flood have abated, the IRT should continue to monitor radio and television broadcasts to track secondary flood hazards as well as emergency response instructions. Special attention should be paid to whether water supplies have been contaminated and whether there has been damage to transportation and medical infrastructures. Personnel should avoid floodwaters, as water may be contaminated by oil, gasoline, raw sewage, or, in extreme cases, decaying carcasses. Water may also be electrically charged by underground or downed power lines. Personnel should also be wary of areas where floodwaters have receded; roads may be weakened and could collapse under the weight of a vehicle. Buildings also may have been structurally weakened and may collapse or have concealed threats. The IMP is designed to support incident managers during the initial stages of a flood, taking action to increase the safety of personnel, as well as the protection of critical infrastructures where possible.