Flooding is the overflow of water onto lands that are normally dry and is the most commonly experienced natural hazard. Desert terrain, snowmelt, and valleys and canyons surrounded by steep mountainous slopes can all contribute to the risk of flooding. When flooding occurs, erosion and considerable deposition of soil and debris can cause additional damage and other hazards. Historically, flooding is the most prevalent, costly, and destructive (on an annual basis) hazard in Utah.
River, Lake, or Sheet Flooding
Overflow of water from excessive river/stream flow, water in lakes, and thin flow across generally flat to gently sloping ground.
Debris flows, and related sediment flows are fast-moving flow-type landslides composed of a slurry of rock, mud, organic matter, and water that move down drainage-basin channels onto alluvial fans.
Shallow groundwater can flood basements and other underground facilities, damage buried utility lines, and destabilize excavations.
Dam and Canal Failure
An unintentional release of water due to the failure of a water-retention or conveyance structure (dam or canal) may occur with little warning. The extent of associated flooding depends on reservoir volume and nature of the failure.
A standing (oscillating) wave in a body of water that is at least partially enclosed and can be induced by earthquakes and other energy sources.
A series of waves in the ocean or a lake caused by the displacement of a large volume of water, such as from underwater fault rupture or landsliding into the water.
Costs of Flooding Hazards
Flooding hazards have caused significant damage to structures and property, resulting in at least 101 fatalities in Utah since 1847, with 80% of deaths from floods and flash floods, 15% from debris flows, and 5% from dam and water conveyance structure failures. Sixteen major flood events since 1923 have caused over $1.3 trillion in damage, and to date, flooding is Utah’s most costly geologic hazard to the economy.