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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.

Should municipalities consider rain barrels to be suitable substitutes for rain gardens? Why or why not? Under what conditions?

  • 1
    I had little knowledge of rain gardens, so thanks for the informative question (& links). I know there are a lot larger rain barrels than 55 gallon. For instance in Bellingham, WA it is common to see 150 gallon attractive form fitting rain barrels resembling a shed on at least 2 corners of a house. I've linked Bellingham's Guide to Rain Barrels.pdf as it has a number of great linked resources on the last page. Harvest h2o is great & those below it may be more applicable to areas outside of WA. – Charlie Brown Jul 18 '13 at 14:18
  • The "Stealth Pond" is a interesting idea, but I can't find any further information about how to actually construct one. Anyone have any tips? – user1459 May 23 '14 at 20:24
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    @Elyce Hello, and welcome to the site. Would you like to post your question on Stealth Ponds as a question in its own right? The "Ask Question" button is in the top-right. As we're a Q&A site rather than a forum, follow-on questions get posted as new questions, rather than being posted under existing questions. – EnergyNumbers May 24 '14 at 8:15
12

There is a conflict of interest between gardening requirements and stormwater requirements:

Stormwater barrels should be kept empty, garden barrels should be kept full.

Though a rain barrel or tank could make a useful water retention device, it loses its value as a stormwater load-reduction mechanism when you retain the water for gardening or other purposes.

To function effectively for stormwater load reduction, a system should be empty at the start of a heavy rain event, and avoid releasing any substantial amount of water during the peak load on the storm water system. The peak load occurs with a certain lag after a certain amount of rain within a limited period.

To function effectively for gardening, a water storage system should retain the maximum amount of water at any given point, which conflicts with the stormwater requirements. This means if you keep your barrel full when possible, then a heavy rain event will quickly cause an overflow and increase the load on the stormwater system.

A compromise could potentially be achieved if the heavy rain events for the region in question mostly tend to occur during winter when water isn't required for the garden. For example, an automatic release valve that very slowly empties the stored water while temperatures are low would mean that water could be retained during summer without manual intervention. In my experience, a system that required manual intervention would be abused (people would commonly either forget to change the setting, or disregard their obligation to do so), so an automatic system would be essential.

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    The TL:DR version: stormwater barrels should be kept empty, garden barrels should be kept full. We found that when we put in tanks there was the psychological hurdle to jump from "save our precious rainwater for the garden" before we could actually use it that way. We'd ingrained the habits of conserving it. – Móż Jul 18 '13 at 1:02
  • One thing they could mandate would be a (say) 10mm drain opening for every X amount of storage, so during rain events while the tank is filling it's also slowly draining. That would spread the storm surge as required, and be pretty easy to check. – Móż Jul 18 '13 at 1:03
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    Thanks @Ӎσᶎ, hope you don't mind that I've used your words! – Highly Irregular Jul 18 '13 at 1:14
  • @HighlyIrregular what's the difference between rainwater and storm water? – Danger14 Feb 7 '15 at 17:45
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    @Danger14 storm water commonly refers to water running off the ground after rain, usually going down a drain. In this case, if you want to reduce the load on the drains during a heavy rain event, you want to prevent water going down the drain until after the load on the system has reduced. It makes sense to refer to water intended to go down the drain as storm water. – Highly Irregular Feb 8 '15 at 3:28
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Short Answer

First of all, let me say that I love rain barrels, and have them installed at both homes I've owned (both older homes that are already fully landscaped). I think rain barrels are great water saving devices, and can provide some buffer against run-off. They're also cheap and easy to install, and can often repurpose existing containers.

However, I would still answer "No, they should not be considered substitutes for rain gardens in building codes".

Why

First of all, we need to understand what the purpose of a building code is. It's not a way to create the best possible residential units. It's a means to provide sort of a lowest-common-denominator solution. A minimum acceptable standard for something - in this case, stormwater management.

Someone such as yourself, who's in tune with these issues, an active gardener, and motivated to consider sustainability, might very well be able to improve upon the building code's solutions. But, the code isn't so much for you, as it is for those who don't care about this stuff.

For rain barrels to perform a stormwater management function, requires some active management on your part. As Highly Irregular said, you have to watch the fill level of your barrels constantly. Most residents won't do this reliably. A 55 gallon rain barrel can fill up fast, so it's easy to envision that in a short time, it might have zero benefit for stormwater management. If the barrel is full, and has to drain via the overflow tube, you get absolutely no drainage benefit. The rain garden is much more work to setup, but in my opinion, once it's working, it should continue to function with less intervention, compared to the rain barrel. If the right native species are planted, once established, you should only have to make sure somebody doesn't completely mow over the garden. Any other maintenance should be few and far between.

Also, building codes primarily serve to govern plans for new buildings. When you have an empty lot that's yet to be landscaped, it's less work to install a good rain garden. After the home/building and yard are complete, and you want to add additional water management, I think rain barrels offer a reasonable retrofit solution.

Parallels

To me, this also reminds me of geoengineering solutions, which I generally tend to be opposed to. For example, a proposal to combat global warming by injecting sulfate aerosols into the stratosphere. True, this would block sunlight, which would have a cooling effect. But, sun is a good thing. Blocking it would have other detrimental effects, and this "solution" does nothing to fight the non-warming problems associated with increasing CO2 levels (e.g. ocean acidification).

Actively managed rain barrels might serve the purpose of stormwater management, but a plastic barrel isn't a plant. Rain gardens are also good because they involve planting native species, keeping greenspace green instead of turning it into concrete, patio or deck area, and they also promote good biodiversity. Rain barrels by themselves don't do these things. The only thing they're assured of doing is saving some water.

Conclusion

Saving water is good. I use rain barrels, and especially recommend them for retrofits, where the yard is already planted (with or without rain garden). I just don't think they're a substitute for rain gardens in building codes.

  • I would argue that local storm water storage that slowly drains into nearby gardens is a much natural solution than sending it through long networks of expensive pipes. With your comment on geoengineering, this should mean you're more strongly opposed to municipal storm water management than you are to barrels or other local solutions. A local system which drains into the ground would help with maintaining aquifers and keeping municipal costs down. – Highly Irregular May 26 '14 at 22:03
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I suppose as with most things it depends (climate, precipitation, erosion factors, season, etc.) But I can't imagine a scenario in which I would rather have rain-barrels instead of say a rain-garden with water absorbing swails on contour. Or better yet a "Natural Swimming Pool" or "Plunge Pool"!

On the advantages of a rain garden over rain barrels:

  • Storage capacity
  • Polyculture ecosystem
  • teaching/training tool
  • nutrient accumulator.

And the disadvantages of rain barrels, factory-made water-storage tanks that:

  • may or may not ever be used in any kind of gardening/landscaping,
  • may or may not become a stagnant pool of mosquito larvae,
  • And even with moderate rainfall the number of barrels needed (6-8 per small home) approches serious eyesore levels.

If pools & rain gardens on contour is too far a leap for "The Decider" to make you may consider building a Stealth Pond instead.

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    +1, and thanks for this. Please can you add a little more about what the advantages are of the rain-garden or the plunge pool, over rain-barrels. – EnergyNumbers Jul 19 '13 at 7:08
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    Where to start...Storage capacity, Polyculture ecosystem, teaching/training tool,nutrient accumulator. Verses factory made water storage tanks that may or may not ever be used in any kind of gardening/landscaping, may or may not become a stagnant pool of mosquito larvae, And even with moderate rainfall the number of barrels needed (6-8 per small home) approches serious eyesore levels. If pools & rain gardens on contour is too far a leap for "The Decider" to make you may consider building a "Stealth Pond" instead. link – Philip Durso Jul 19 '13 at 8:12
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    Great stuff Philip - I'll copy & paste that comment into your answer (and you'll be able to do the same yourself) - comments are transitory, so we try to get all the solid info into answers, rather than comments. – EnergyNumbers Jul 19 '13 at 8:28

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