Flood Causes

Floods are caused by numerous environmental, seasonal and human factors. All flooding can be dangerous and potentially deadly, although infrastructure and property damage are among the most common outcomes. Although large-scale floods are generally thought of as the most dangerous, smaller floods and flash floods can cause much harm as well. As little as two feet of running flood water can sweep away a large automobile and drown a person swept up in its currents.

Geography

• Areas near rivers and other water bodies or areas at low levels relative to the surrounding terrain can be prone to flooding. When water rises too much it can flood over its banks or shores and into adjacent areas. The water will settle at the lowest possible point, flooding any areas that are at or below the current water level. In areas where the ground is dry, nonporous or otherwise incapable of absorbing water, flooding can occur as a result of sudden or seasonal rains as well.

Weather

• Hurricanes, tsunamis and even severe rain storms can cause flooding in areas that have certain geographical features. Flash floods, which are distinguished from other floods in that they occur in a matter of hours, are often the result of heavy rain in low-lying areas. The effects of floods caused by weather can vary. Flash flooding usually diminishes in as little time as it occurred once the source of rain is gone. Floods from tsunamis and hurricanes can last for days or weeks. In addition to conventional water damage, these floods can also aggravate damage caused by forceful winds and high water, leaving significant destruction.

Technology Failure

• Occasionally, permanent structures such as dams and temporary flood walls or sandbags prove inadequate to hold back water. In permanent dams, this can be because of a design flaw or slow, extensive wear over time from water pressure and other erosive elements. Temporary precautions such as sandbags can fail for numerous reasons. These include improper placement and inadequate volume. The extent of seasonal flooding caused by rain or melting snow can be difficult to predict; sandbags sometimes fail because the water is higher than the sandbag walls are erected to hold.