37 inches = 86 billion gallons
If there’s one thing on TV we don’t do, really can’t do, is math. Ask the audience to calculate something and you’ve lost their attention as the story whizzes forward. Here we can tackle it though. I want to share a mind-boggling number and an easy formula I learned while reporting our story on how well ecoroofs work.
Portland gets about 37 inches of rain each year. That adds up to 86 billion gallons of water falling on our heads, grass, driveways, parking lots, roofs and trees. The city’s big headache is that we’ve paved over so much of metropolitan Portland that most of that water is running down into the storm sewers.
So the city is encouraging green roofs and now even homeowners can get into the act.
But how much ran runs off the average house in a year in Portland? You can do the calculation yourself.
The Square Feet of the roof x 23 = gallons of runoff in a year.
Casey Cunningham at the city’s Bureau of Environmental Services elaborates: ”In more detail: square footage times 3.083 (which is 37 inches of rain converted to feet) times 7.48 (the number of gallons in a cubic foot)”
A small home with a 1,000 square foot roof would see 23,000 gallons run off annually. That’s more than a drop in the bucket. Building with ecoroofs on them can capture and hold close to 50% of the water that falls on them.
The city’s not only encouraging businesses to install ecoroofs, it now wants to promote this on homes too. There’s an event called Ecoroof Portland 2010 coming up March 12 & 13 where you can learn all about it. You can also learn how to apply for money from the city. Incentives could offset up to $5 per square foot of your costs. The event runs from 10am to 6pm at 101 NE Weidler in Portland.
The Field Journal brings you notes and stories from the environmental beat in Oregon and the Northwest.
