Where does the rain go?

Did you know that stormwater runoff is the largest cause of pollution in Puget Sound? Here in Seattle, if it's not raining today, just look up the weather forecast and you'll see it coming. The traditional Seattle rain is often light enough to prompt a question of, "Is it raining?" You actually have to stand outside for several minutes to be sure. But we also get heavy rain, the type that flows down the street in a visible river and drenches you as you run across the street. Due to climate change, the Seattle area will supposedly see much more of this drenching rain. 

Where does the rain go after it reaches the ground? If it lands on dirt or vegetation, it soaks into the soil, which acts as a natural filter. But if it lands on a hard surface - a roof or road - it flows into storm drains, which lead to rivers, lakes, or seas. This is no longer clean rainwater. It is contaminated with oil and gas from cars, heavy metals, and other compounds that are toxic to animals and people.  We do have sewage treatment plants that filter this water. But major storm events overwhelm the system, and untreated water can flow directly into places where it impacts the health of salmon and other species, including people.

The more heavy rain we get, the larger the problem. I'm writing an article about stormwater management that will appear in Seattle Business magazine later this year (I'll add a link when it publishes.) The article discusses several specific projects in the Puget Sound region that are addressing this issue. But I just felt compelled to blog about it now. 

There are many possible approaches to mitigating stormwater runoff, and they can all be found in commercial and residential buildings in the Seattle area. 

• Add a green roof. Putting vegetation on the roof serves several purposes: It cools the building in the summer, looks good, provides visible evidence of green building practices, and the plants absorb stormwater so that it never reaches the street. But this strategy is only workable on flat roofs, and the gardens do require maintenance. 
• Store rainwater in a cistern. Cisterns collect rainwater flowing out of gutters and filter it. The water can then be used for irrigation in the summer. But cisterns do require sufficient space and many of them are not especially attractive.
• Install a rain garden. If rain gardens are properly designed, they collect water that would otherwise flow into the street and filter it down through the soil. They also add curb appeal to houses and neighborhoods. Not all properties, however, have a suitable site, especially those built on a hill. If water pools in the rain garden or flows out of it, that defeats the purpose.
• Replace sidewalks or parking areas with permeable pavement. This walkable and driveable surface is porous, so that stormwater soaks into the sand layer below. But it is more expensive than standard concrete and has a look that not everyone appreciates.

In the course of researching the Seattle Business article, I visited Clearwater Commons, a residential development in Bothell, a suburb northeast of Seattle. The development is using all these solutions and more. But more on that in my next blog post, along with a tie-in to the diesel car fiasco.