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!


6 comments:

Rose said...

Now I'm getting even more excited about creating one of these myself! Thanks for the additional information, Rose; this is the perfect example of one simple thing a person can do that multiplied over many gardens could make a huge difference. I'm interested in where you sited your rain garden and if you directed downspouts towards it.

Thanks for the link love; now I wish I had used this for my Sustainable project, too:)

garden girl said...

That's fantastic Rose! Your rain garden is also pretty, and great for the pollinators with its native plants.

We don't have a rain garden, but we do have a swale that serves the same purpose. There was never anything planted in it before I came here. I'm still learning what will thrive there since it's shady and stays wet for a long time. So far the river birch, red-twig dogwoods, cardinal flowers, and heleniums are doing well in the always-moist spots. It's the spots that are flooded for days, (sometimes weeks,) after a storm or snow melt, and bone dry most of the summer that challenge me most.

Sissy said...

I surely learned something new today! The first is about rain gardens. The second? I'm awful at math!!

rambleonrose said...

Rose--I agree that this is something simple that people can do to make a different. I look forward to reading about your own rain garden creation in the future! I did direct a downspout into mine, which I'll address in a post soon!

GG--It's definitely challenging to find plants that can take those extremes! I have had some hits and misses too.

Sissy--Don't worry, I'm terrible at math too! That's why I had to find a website to tell me exactly how to calculate the volume, then I used a calculator to actually figure it out!

Plant Tomatoes said...

You know how precious freshwater is to life.You probably also know that freshwater is becoming increasingly scarce due to pollution, misuse, overuse and climate change.

So when someone asks you "why plant a rain garden?" you can tell them that you are doing it to help keep clean, fresh rainwater out of the sewer system and you are doing your part to reduce pollution and preserve our water systems.

VMware Classes Online said...

We don't have any space in here...since we lived in the fourth floor in a building..a condominium building of course..No matter how much I love planting plants I guess I need to stick with my pots. :)

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