In much of Marin, gravity is the biggest factor in water damage. Homes on hillsides in Mill Valley, Sausalito, Tiburon, Belvedere, Larkspur, San Rafael and Kentfield catch rain on the roof and also receive runoff from every lot above them. Good drainage moves that water around and away from the house. Poor drainage sends it into crawlspaces, lower floors and foundations.
As of the Climate Prediction Center's October 8, 2026 ENSO discussion, an El Niño Advisory is in effect, and NOAA says a strong-to-very strong El Niño is likely through January–March 2027. NOAA is also careful to say that a stronger event makes El Niño-like impacts more likely, not guaranteed. El Niño winters have historically tilted Northern California toward wetter conditions, but individual seasons vary, and no outlook can tell you when or where a specific storm will hit. Watch the CPC seasonal outlooks and the National Weather Service Bay Area office for forecasts as the season unfolds.
Gutters collect roof water and are your first line of defense. In Marin, tree cover makes them fill quickly. Oak leaves, redwood needles, eucalyptus bark and pine needles can clog a gutter in a single windy storm.
Our sister site covers gutter repair and has a gutter cleaning guide for Marin's tree cover.
A downspout that dumps water at the base of your foundation defeats the purpose of the gutter.
On a hillside lot, the uphill side is where trouble starts. Look for:
Common fixes include regrading, French drains, curtain drains, and waterproofing below-grade walls. These are jobs for licensed contractors and sometimes require a geotechnical or civil engineer, especially on steep slopes.
Many hillside homes have patios, decks and driveways that drain through small area drains. Test each one with a bucket of water before the season. Driveways that slope toward garages need a working trench drain at the bottom, and keeping it clear of leaves is critical.
After the first significant rain, look in your crawlspace or basement. Standing water, wet soil, or water lines on foundation walls are signs drainage isn't keeping up. A sump pump can help, but fixing the source of the water outside is usually better. See storm damage and flood cleanup.
If you see signs of slope movement like new cracks, tilting walls or bulging soil, especially during or after heavy rain, contact your city or town and a licensed professional, and follow any official guidance. Sign up for AlertMarin for emergency notifications.
Walk your property after each big storm. Note where water collected, where gutters overflowed, and anything new in the crawlspace. Photos help a contractor diagnose problems later.
On hillsides, water doesn't respect property lines. Runoff from an uphill neighbor's driveway or downspouts can end up against your foundation, and your discharge can affect the home below you. If you notice a recurring problem, start with a friendly conversation and photos taken during a storm. Sometimes a shared solution, like a drain along a property line, works better for everyone. For more complicated situations involving slopes, retaining walls or easements, consult your city or town and licensed professionals before making changes.
If water gets inside despite your best efforts, start drying quickly and document everything. Read the first 24 hours after water damage, and request help from an independent local provider.
Several feet away, or into a solid drain line to an appropriate discharge point; avoid unstable slopes and neighbors' property.
Ponding at the foundation, overflowing gutters, damp below-grade walls, or water in the crawlspace.
Licensed contractors, sometimes with a geotechnical or civil engineer on steep slopes.
It can contribute to drainage problems. Document it and talk to your neighbor and local officials if needed.
Some drainage and grading work requires permits. Check with your city or town.
This article is general information, not legal, insurance or medical advice. Sources are linked in the text.