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My county requires rainwater management to be incorporated into lot plans for new construction if a certain percentage of the lot is impervious. This seems a sensible measure.

We are under the impression that rain gardens are the only approved method for managing runoff (if a percolation study determines that the site's soil can support one). Rain gardens benefit the community by reducing erosion and filtering pollutants.

It seems to me that rain barrels can achieve the same benefits. The only significant differences between the mechanisms that I can think of are

  1. the storage capacity and
  2. retention time.

Rain gardens "store" water temporarily and have a much higher capacity; rain barrels store only about 55 gallons but can hold that water indefinitely.

Because I'm an avid gardener, I'd much rather have rainwater available for watering my garden and reduce my reliance on municipal water. There is also some concern that rain garden performance degrades over time unless well-maintained. I don't think there's a similar risk to rain barrels, but if there were I imagine it'd be much easier to rectify a failing rain barrel than a failing rain garden.

Can rain barrels be considered to be suitable substitutes for rain gardens? Why or why not? Under what conditions?

  • That's interesting, it's like a dry well that you plant flowers in. – Tester101 Jul 17 '13 at 16:40
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I would think not, for a few reasons.

Water doesn't drain at a calculable rate from a rain barrel.

A rain garden would have a fairly consistent drainage rate, whereas a rain barrel could theoretically be full indefinitely. There is no guarantee that a homeowner who has a rain barrel, will use the water from the rain barrel.

Rain barrels don't capture all the water.

A rain barrel only captures the water from a structures roof, so only a portion of the water that falls on the property has the potential of being contained. A rain garden can capture water that falls not only on the structures roof, but also water that has fallen to the ground. The rain garden can also; theoretically, capture the overflow of other nearby rain gardens.

Rain gardens are harder to remove.

A rain barrel can easily be removed, either purposefully or accidentally. A rain garden would require quite a bit of effort to remove, and would not likely be removed accidentally.

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Can rain barrels be considered to be suitable substitutes for rain gardens? Why or why not? Under what conditions?

That is something only your county can answer as they're the ones that make the rules you need to abide by.

You'd have to have a pretty large array of rain barrels to handle as much water as you can with a rain garden as you noted.

There's no reason you can't mix the two. Your structure, if like most, will have multiple downspouts. See what the requirements are. You could have rain barrels on some downspouts, rain gardens on others. You can even combine the two and have the overflow from your rain barrel empty into a rain garden.

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As OrganicLawn mentioned, only your county can give you an answer for sure, but one reason I could see for them not being a good substitute would be the rainfall patterns where you live.

Here in the Great Lakes, and I suspect it is similar in VA, we get a lot of rainfall in spring and early summer. Our average precipitation days that time of year are 12/month, and it isn't unusual to have rain 2 or 3 days in a row. I have 1 rain barrel which pulls from less than 1/6th of my roof. It is overflowing by the end of one spring or early summer storm. I would need at least 2 rain barrels (maybe more) per downspout to capture the rain from a single storm, and the thing is, that time of year I am doing very little supplemental watering in my garden, because by the time the garden dries out, another shower is on the way, so really I would need enough barrels to capture the rain from many storms. Even if I hooked up 4,5,6 rain barrels to each downspout so I could capture all the rain from subsequent storms, I would never be able to use all that water before new storms came. And at that point, it would probably make more sense to put in a huge cistern. My rain garden, on the other hand, which captures runoff from my driveway, absorbs and incredible amount of rainfall and has never overfilled.

There is a reason permaculturists advocate for storing your water in the soil whenever possible - it really is the least expensive and most practical method for storage. But certainly, a combination of strategic rain barrels and rain gardens is a terrific solution for most of us.

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  • Your answer, particularly "Even if I hooked up 4,5,6 rain barrels" reminds me of a question I posted to sustainable living: "What are the larger-scale options for storing rainwater?" sustainability.stackexchange.com/q/954/570 – Jeromy French Jul 17 '13 at 19:54
  • for many areas of eastern North America unless you start collecting totes which are cheap but ugly you cannot store enough water in the spring to get you through the dry times in the summer. – kevinsky Jul 18 '13 at 0:17
  • Well, some do use cisterns, but a common permaculture option is digging long, shallow swales and filling them with organic matter (straw, wood, etc.) that can soak up tons of water and then release it slowly when the soil around it dries out. Artificial ponds can also be used to catch the water, if you can direct the runoff to them. I'm sure there are many other options, but those are two I know. – michelle Jul 18 '13 at 12:57
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    @JeromyFrench If you have a raised deck I saw something pretty neat once but forget what it is called. There was this huge bladder bag that you install under your deck to store rainwater. I think they were custom made. Not cheap from what I remember but looked like one of the easiest solutions. – OrganicLawnDIY Jul 22 '13 at 17:47
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The purpose of that requirement is probably to keep the rainwater onsite and out of the storm drains. Without knowing the details of the code, they probably require you to be able to retain all of the water from a 5-year peak storm or something like that. When designing your storm water system, that's the volume of water you need to deal with, whether you're doing a rain garden or some other system.

I would think that if you can demonstrate that your system can detain the same volume of water that it would be OK, but I agree that if you're just putting the water into regular barrels then once they're full you can't retain any more water.

Perhaps you can work out a hybrid system where your barrels drain slowly into a smaller dry well. That would let you use the water in the day or two after a rainfall, while also allowing the system to function as required if nobody is around to use the water.

Regardless of what you decide you want to do, you'll almost certainly want to get the advice from an engineer or water management specialist.

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