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Hydrology Sub-Committee George Smith, Coordinator

Floods are defined by the National Weather Service (NWS) as "Any high flow, overflow, or inundation by water which causes or threatens damage." More specifically, flash floods are "A rapid and extreme flow of high water into a normally dry area or rapid rise in a stream or creek...". The Federal Emergency Management Agency (FEMA) National Flood Insurance Program (NFIP) defines flooding as"




"A general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or of two or more properties (at least one of which is the policyholder's property) from:

  • Overflow of inland or tidal waters; or
  • Unusual and rapid accumulation or runoff of surface waters from any source; or
  • Mudflow; or
  • Collapse or subsidence of land along the shore of a lake or similar body of water as a result of erosion or undermining caused by waves or currents of water exceeding anticipated cyclical levels that result in a flood as defined above."

However you define them, floods and flash floods are the most common and dangerous natural hazards in the world. According to FEMA, the NFIP since 1978 has paid $33.2 billion for flood insurance claims and related costs. They continue in saying that any particular home has a 26% chance of being damaged by floods during the course of a 30-year mortage term and that flash flooding is the leading cause of weather-related deaths in the U.S.

A key factor in reducing loss of life and damage to property is the collection of real-time hydrologic data to forecast the potential rainfall from a storm event and the subsequent effect on the nearby rivers and streams. This involves the use of advanced radar systems ground-truthed with telemeterd data from monitoring stations. Additional tools such as accurate digital models of ground terrain, incorporated with the radar and real-time data, can provide accurate forecasts in many watersheds.

Let the NHWC assist your community to be better prepared the next time the rains fall. Our conferences and workshops highlight the many technological advances in hydrologic data collection, forecasting, and warning disseminations.

For more general information about floods, check out these resources:

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