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Welcome to the Flood Preparedness Website!

Where floodwaters flow - check it out!

Floodplains are generally flat areas adjacent to watercourses or the sea where water flows in time of flood or would flow, if not for the presence of flood protection. So, even if a community has flood protection provided by levees or sea walls, that community is still in a floodplain – it is just better protected than it would be without levees and sea walls because while levees and sea walls reduce the risk of flooding, they do not completely eliminate the risk or consequences of flooding.

However, floodplains are not always flat. They can also be sloped and curved as is the case with alluvial fans.

Because floodplains vary so widely in size, shape, and potential depth of flooding, probably the best way to think of floodplains is that they are any land area that is subject to inundation by flood waters from any source. And, this is where things can get a bit tricky: we can’t always see our potential flooding sources because of distance or other reasons, or we don’t think of small creeks or streams producing extreme flooding.

Due to California’s diverse geography, we have all three major types of floodplains: alluvial fan, coastal, and riverine as well as other, less common, types of floodplains.

General Locations of Flood Hazards

Map is representational only and does not include all floodplains in California. (Source: California Department of Water Resources, 2013)

Alluvial Fan Floodplains

Alluvial Fan Floodplains are areas on alluvial fans that are subject to flooding. Flooding on alluvial fans can be comprised of water, water that is laden with debris, and water that carries so much debris it is called “debris flow” flooding. These floodplains vary in size. Alluvial fans experience at least three different types of flooding, and flooding on alluvial fans can impact land and floodplains adjacent to the fan. For more information about alluvial fan floodplains, click here

Coastal counties

Coastal Floodplains are generally flat areas bordering the ocean where water flows during a tsunami or tidal storm surge or would flow if not for the presence of flood defenses like sea walls. These floodplains vary in size. Coastal floodplains experience at least two different types of flooding, and flooding on coastal floodplains can impact land and other floodplains adjacent to coastal floodplains. For more information about coastal floodplains,
click here

FEMA 100-yr riverine floodplains

Riverine Floodplains are generally flat areas bordering rivers and streams where water flows in time of flood or would flow if not for the presence of flood defenses like levees. These floodplains can be quite narrow in canyons and up to several miles wide in valleys. Like alluvial fan and coastal floodplains, riverine floodplains experience different types of flooding, and flooding on riverine floodplains can impact land adjacent to the floodplain. For more information about riverine floodplains, click here

Bottom line: living in floodplains involves both risk and consequences.

So, BE AWARE, BE PREPARED, and TAKE ACTION!