Monday, March 28, 2011
Why you should have a rain garden
A few weeks ago we experienced an intense rainstorm, and as I stood looking out my back door I saw my rain garden in full effect, filled to the brim. This reminded how I've wanted to figure out how to quantify just how much water the rain garden collects. After a quick internet search, I found a handy formula to calculate the cubic feet of water contained by the rain garden when it's full, and how many gallons that equals.
Based on these calculations (3.14 x [length x .5] x [width x .5] x depth x 7.48), my little rain garden holds about 140 gallons of water. That means that if it gets filled ten times in a year, it absorbs 1,400 gallons of water! (In the link above I used the elliptical measurement because my rain garden is an oval, not a rectangle.)
Now, none of this is hardcore calculus or anything, and if my measurements are found to be wrong I welcome corrections from anyone with a stronger understanding of math than me! I also found round measurements that didn't account for the length of the water feature. Using this calculation my rain garden clocked in at a still-respectable 94 gallons capacity.
Assuming either calculation is correct, that's pretty impressive. Approximately 100 gallons of water held by one little 6'x4'x1' rain garden! If more people could help absorb 100 gallons at a time in their gardens (while enjoying beautiful native plants like milkweed, cardinal flower, golden alexander and sedges), imagine what a difference that would make for our aquifers, rivers, lakes and stormwater systems! If a little rain garden like mine can absorb over 1,000 gallons of water a year, how much pollution, fertilizers and sediment could be kept out of waterways by 10 more rain gardens of a similar size? What about 100 more?
I spent two days digging this rain garden, which was the most difficult part. Finding the right plants was fun, and it's needed very little maintenance since it was completed. (I have to dig out leaves and mulch occasionally, which is partly my fault for making the sides too steep. At 6'x4', that's still easier to accomplish than my regular weeding chores.) A couple days' work equals roughly 1,000 gallons of water conserved a year. Not a bad equation, if you ask me!
I had been planning this post for a while, but I was finally motivated by two things to get it out there. First, this is part of Jan's Gardeners Sustainable Living 2011 in honor of Earth Day on April 22nd. Visit her at Thanks for Today to read more! Also, Prairie Rose posted about a rain garden information session she attended and I'm piggybacking on that too. I encourage you all to seriously investigate planting a rain garden to help keep stormwater and runoff out of our sewers, rivers, lakes and oceans and to help recharge our aquifers. To help that, I will post more about how to site a rain garden and what are appropriate plants to use. Or, if you don't feel like waiting for me, check out the Prairie Rivers Network (link is also on my sidebar under Chicago-Area Resources). They have lots of great information!