California Flooding: What Every Property Owner Should Know

California doesn't flood often, but when it does, it floods hard. Months of dry weather bake the ground until it can barely absorb water, and then a single storm system can drop a season's worth of rain in a few days. We ship flood and storm protection out of Lake Forest, CA, so we've seen what these storms do up close. Here's what you should know, and how to get ready before the next one arrives.

Why California floods the way it does

Most of the state's big floods come from atmospheric rivers, long, narrow bands of moisture that stream in off the Pacific and stall over the coast and mountains. A strong one can carry more water than the Mississippi River, and they often arrive in back-to-back waves. The first storm soaks the ground. The ones after it have nowhere to go but downhill, into streets, garages, and ground-floor businesses.

The kinds of flooding you'll see

• River and creek flooding. Prolonged rain pushes rivers and creeks over their banks and strains the levees across the Central Valley and the Delta. This water rises slowly, but it can sit for days.
• Flash flooding. Intense rain on steep terrain or hard, dry ground turns dry washes and canyons into fast-moving water in minutes. This is the most dangerous type, because there's almost no warning.
• Burn scar debris flows. After a wildfire, scorched soil repels water like pavement. Heavy rain on a burn scar can send mud, rock, and debris downhill fast, and the risk lasts for several years after the fire.
• Urban flooding. Storm drains are sized for normal storms, not atmospheric rivers. When they back up, water collects in low streets, underground parking, and anywhere the grade slopes toward a door.
• Coastal flooding. High tides, storm surge, and big winter swells combine to push seawater into low-lying coastal neighborhoods and harbors.

When flood season hits

California's flood season generally runs from November through April, with the heaviest storms usually landing between December and February. In the spring, snowmelt from the Sierra Nevada can keep rivers high long after the rain stops, especially after a big snow year. Summer isn't completely safe either. Monsoon thunderstorms can cause flash floods in the desert and mountain areas of Southern California.

What's at stake

According to the California Department of Water Resources, more than 7 million Californians live in a floodplain, and every one of the state's 58 counties has had a federally declared flood disaster. FEMA estimates that just one inch of water in a home can cause around $25,000 in damage. For a business, the real cost is often the downtime: flooring, drywall, inventory, and days or weeks of lost revenue.

Two things catch people off guard. Standard homeowners and commercial property policies generally don't cover flood damage. And a new flood insurance policy through the National Flood Insurance Program usually has a 30-day waiting period, so buying one when the forecast turns bad is already too late.

How to prepare

• Know your risk. Look up your address on FEMA's flood maps and your county's flood and burn scar maps. Being outside a mapped flood zone doesn't mean you're safe. Many flood claims come from outside them.
• Review your coverage. Ask your agent what your policy actually covers, and consider flood insurance well before the rainy season.
• Clear the drainage. Clean gutters, downspouts, and the storm drains near your property before the first big storm, and make sure water flows away from your foundation.
• Protect the openings. Garage doors, storefronts, and low entryways are where water gets in. Have a barrier staged and ready, not on backorder.
• Watch the forecast. Sign up for your county's emergency alerts and pay attention when the National Weather Service issues a flood watch or an atmospheric river forecast.
• Have a plan to leave. Know your evacuation route, keep a go bag ready, and never drive through a flooded road. Just 12 inches of moving water can float a car.

Skip the sandbags

For most people, flood prep still means waiting in line for sand and spending an afternoon filling bags that leak at every seam. The DPALEX Flood Barrier is a faster way to do it. The panels lock together by hand into a continuous wall, seal against the ground, and hold back up to 27 inches of water. A typical entryway is protected in about 5 minutes, and when the storm passes, you rinse the panels off and stack them for next time.

Atmospheric rivers also bring wind, and a roof that leaks during a storm needs to be covered fast. Our Standard and Heavy Duty roof tarp kits come with everything you need to cover a damaged roof in one box.

Common questions

Does homeowners insurance cover flooding in California?

Usually not. Standard homeowners and commercial property policies exclude flood damage. Flood coverage is sold separately through the National Flood Insurance Program or private insurers, and new policies typically take 30 days to kick in.

What is an atmospheric river?

It's a long, narrow band of water vapor that flows in from the Pacific. When it hits the coast and the mountains, it can dump several days of heavy rain and snow. Atmospheric rivers supply much of California's water, and they also cause most of its major floods.

Am I at risk if I'm not in a flood zone?

Yes. Flash flooding, urban flooding, and debris flows can all hit properties outside mapped flood zones, and a large share of flood claims nationwide come from outside high-risk areas.

Get ready before the rain does

The best time to prepare for a flood is a dry week in October, not the night before the storm. The DPALEX Flood Barrier ships within 1 business day from our warehouse in Lake Forest, CA. For large perimeters, municipal orders, or pallet quantities, request a quote. Need it fast? Call us at 888-288-8118.