Kirkland has experienced severe weather events in the last few years, and, as you know, we had a major rainstorm that caused flooding across much of the state. Sometimes you’ll hear the media talk about a “10-year storm event” or maybe a “100-year event” in association with heavy rain, but what does that really mean?

What makes a 10-year storm?

A 10-year storm is a rain event with a 10% chance of occurring in a year. Thus, on average, we would see one every ten years. We can follow this pattern for 25-year storms (4% chance per year), 50-year storms (2% chance per year), 100-year storms (1% chance per year), and so forth.

Do these rainstorms have to occur over one day? Multiple days?

Many large storm events occur over a single day, but some can persist for multiple days. When referring to a “10-year storm event,” that is typically over 24 hours.

In Kirkland, a 10-year storm means it rains 2.6 inches in one day! For reference, a typical rainy day sees about 0.5 inches of rain. That’s 420% more!

What happens during these storms?

It may seem obvious, but soil gets wet and reaches a saturation point. Any rain that falls after this saturation point becomes runoff and flows into our streets, storm drains, and creeks. Also, rain that hits hard surfaces will flow directly into this runoff drainage system. When our storm drains and pipes get filled, we see flooding. Runoff also takes everything with it; the water is polluted with any pesticides or fertilizers left on your yard  and flows into our creeks and, eventually, Lake Washington.

How does the City work to prevent flooding during these massive rain events?

The City of Kirkland works each year to identify areas that experience consistent flooding, even in years without large storm events. Once we identify these spots, we continue to monitor them while working to create long-term solutions. Examples of solutions include planting roadside rain gardens and installing underwater vaults to hold overflow. We encourage residents to report any flooding they see in their neighborhoods, as local knowledge is invaluable in creating effective solutions. By working together, we can make Kirkland more resilient to severe weather events.

To report flooding, call: (425) 587-3900

What can you do to prevent runoff?

The simplest way to prevent runoff at your home is to plant trees, shrubs, and other plants that create deep roots. The deeper the roots, the more water the plant can absorb. Our grass lawns, while picturesque, aren’t great at developing these roots. Most lawn grass  isn’t native to Washington and therefore doesn’t have the roots that are ready for heavy rain.

What are the best plants to plant? Native plants! These plants are rain-ready and can better withstand a 10-year storm event. Consider planting ferns, vine maples, and Pacific rhododendrons.

Are your downspouts connected to underground pipes that lead to the road? Disconnecting downspouts and allowing that water to infiltrate in your yard will also slow runoff. If you’re interested in disconnecting your downspout, check out our Yard Smart program. We offer rebates to households that disconnect and make their yards more stormwater-friendly, like with rain gardens.

Now you know! Hopefully, this cleared up some of the stormwater “lingo” you might hear thrown around in weather reports and news articles.

If you’re interested in learning more about managing stormwater, the City of Kirkland offers a rebate program (www.KirklandWA.gov/YardSmart) and online resources. These can provide guidance on making your property more resilient to heavy rain events. Visit our website (www.KirklandWA.gov/Stormwater) for more information. If you have any questions, reach out to me at stormwater@kirklandwa.gov.