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Flood Education

Climate change is expected to bring even more extreme weather to California than usual: longer, drier droughts and more ferocious storms, both of which can increase flood risks

Dry soils from multi-year droughts create perfect conditions for dangerous flash floods. And heavy downpours often lead to dangerous flooding conditions. The Golden State, for all of its natural beauty and benefits, is a land of extremes. So just remember, even if we’re in a drought, “Flood Prepare California!”

Floodplain Types

  • Alluvial Fan Floodplains: Alluvial fan floodplains are the most complex kind of floodplain in California because of the way alluvial fans are created. Learn more >>
  • Coastal Floodplains: Coastal floodplains are areas near the coast that are subject to flooding from various tidal, storm and tsunami events. Learn more>>
  • Riverine Floodplains: Riverine floodplains are the most common floodplains in California (see figure 1). Low lying, generally flat areas adjacent to and near rivers, creeks and streams that flood when water overflows the banks are all considered riverine floodplains.  Learn more >>

Types of Flooding in California

  • Alluvial Fan & Debris Flow Flooding: An alluvial fan is a fan-shaped buildup of sediment found at the base of steep mountain canyons. Alluvial fan flooding is characterized by relatively shallow depths, high velocity, and moving soil and sediment, creating uncertainty about where rising water will travel. Alluvial fan flooding is a concern primarily in central and southern California. Learn more >>
  • Coastal Flooding & Tsunami Dangers: Storms can cause flooding through a process known as "storm surges," which is when ocean waves are significantly larger than normal. If a storm event corresponds with a higher than normal tide, extensive flooding can occur. Learn more >>
  • Flash Flooding: Flash floods are the number one weather-related killer in the U.S. because they can roll boulders, tear out trees, and destroy buildings and bridges quickly. A flash flood is a sudden, rapid flooding of low-lying areas typically caused by intense rainfall. Flash floods can also occur from the collapse of a man-made structure or ice dam. Learn more >>
  • Localized/Stormwater Flooding: Localized flooding occurs in both urban and nonurban areas during or after a storm. Any storm, particularly slow-moving, steady rain storms, can overwhelm drainage systems. When the system backs up, pooling water can flood streets, yards and even the lower floors of homes and businesses. Even less intense storms can cause this type of flooding when leaves, sediment and debris plug storm drains. Learn more >>
  • Riverine Flooding: Riverine flooding occurs when rivers, streams and lakes overflow their banks. This includes flooding caused by levee failure and channel erosion. Learn more >>