Monday, 21 February 2011

West Dean Rain Gardens

Last year I was lucky to be sent a list of West Dean's winter/spring workshop programme with the invitation to select one if I so desired for 'review purposes'. It was a mouthwatering prospect and my shortlist finally boiled down to either my vegetable guru Joy Larkcom in a rare foray from her home in Northern Ireland, or Nigel Dunnett on the subject of Rain Gardens.

I finally plumped for the latter and thus found myself on an aptly drizzly day driving down to West Sussex a couple of weeks ago for an absolute treat. Whilst I'm an admirer of Nigel Dunnett's work, I really only had the vaguest notion of what a rain garden actually is. It's a subject which has yet to catch on in Britain in a big way: the pioneering countries are the USA, Germany and Australia. Having spent a day thoroughly immersed in the subject and taking frantic notes, it's something I believe which needs to be taken much more seriously here too.

The Problem

No matter what you might think about the validity of climate change, there's no escaping from the fact that storms are on the increase in both their frequency and intensity. This is made even worse by the increased runoff we see as our environment changes from natural ground cover (typically 10% of rainfall) to increasingly built up areas (55% when surfaces are 75-100% impervious).

The usual response is to provide an engineered solution i.e. replace the current drains with even larger pipes and managed via the depressingly named SUDS (Sustainable Urban Drainage Systems). Nigel argued these aren't really sustainable enough and their design is often downright dangerous and usually very ugly. Cue lots of pictures of fenced off deep rectangular shaped lagoons ringed with vegetation and warning signs.

The Solution

Nigel proposed a landscape based solution (aka Rain Garden) where surface runoff is managed via a number of absorbent surfaces which capture the rain and let it flow away much more slowly. Features include the more familiar (though optional) trendy green roof as the first point of capture. Nigel then advocated disconnecting the downpipes from our drains and instead letting the water flow out into a bed of plants away from the building - the actual rain garden itself. It sounded a very scary thing to do, but Nigel admirably demonstrated via a number of case studies that aesthetically pleasing results are achievable, with less pollutants (as the beds also act as a biofilter) and at a much lower cost than using a SUDS solution.

We came away convinced, but I suspect we will need our government to adopt an approach like they have in Portland, Oregon where households and businesses pay for the amount of water which enters their drainage system.

Can I apply it to my garden?

Many of the examples we saw on the day were from the public planting arena, but the handouts we were given show it can be scaled down for our gardens. It involves quite a lot of calculations though, so I don't think it's currently a DIY solution. I also expect that more guidance will become available in the future to help us to adopt this approach ourselves. For example, a book by Nigel and a number of colleagues is due out in May on how home owners can build their own green roofs.

Also in May, The New Wild Garden will be revealed at Chelsea Flower Show. Inspired by William Robinson's ideas and Nigel's research, it will demonstrate a garden-scale rain garden for us all to debate and ponder over.

How was the day?

Nigel Dunnett is a very engaging speaker whose audience on the day was a mixed bunch of garden design students, West Dean Gardens volunteers and interested members of the public like me. We were all made thoroughly welcome by the day's organiser Annie Guilfoyle and everyone participated in the discussions. The sandwich lunch with cake and fruit to follow was good quality too. I'm looking forward to returning at my own expense for another study day. It's an inspirational thing to do in the winter, when practical gardening activities take a back seat.

I also managed a quick run round the gardens a couple of times in the rain. Even on a miserable day in February it was enough for me to fall in love with the place. Have a look at a recent Sign of the Times Friday Bench for a quick taster. There's more to come soon :)

Further reading

NB we were given loads of handouts on the day, and told there's vast riches to be found if you Google Rain Gardens. I've tracked down most of the ones we were given as your starter for 10, should you wish to know more:
These documents and websites are much more readable than their titles suggest! Finally, Nigel has written a book about Rain Gardens which is aimed at landscape architects and designers but is still a most interesting read.

13 comments:

  1. I am increasingly finding rain gardens fascinating and would have loved this talk. I am all for the unengineered approach especially given the cost. As you know my patio regularly flood down one end when we have heavy rain, to create drainage linked to the sewers would have cost £600. Instead we have dug out the corner of the patio, planted marginal plants and now when it rains whilst the patio still floods it is only briefly and the water soaks away quite quickly

    ReplyDelete
  2. very interesting indeed!
    And West Dean is on my to do list.
    Thanks for this
    Best
    R

    ReplyDelete
  3. How fascinating - not something I had given that much thought to as yet. I'm very jealous of you going to West Dean. After they cancelled my 3 day course a year or so back I haven't been able to find something that is just right for me. I don't just want to do a day course as it is such a lovely place I'd like to spend a weekend there absorbing.

    ReplyDelete
  4. PG - it struck a chord with me that you'd have loved this when we discussed your patio on Saturday. Nigel showed an example of a company car park in Coventry which started to flood when it was expanded.

    The solution was to dig up an unused area outside the staff canteen, put decking over where the pipes came away from the building to hide what they were doing and to create a rain garden next to it with a substrate which looked very much like hardcore. Result = a very pleasant spot for staff to take lunch, no flooding and lots of publicity about it in the co's literature.

    Robert - thought you might :) NB no planting plan is used either, just a mix of suitable plants for the climate. In most cases the kind which are drought tolerant but don't mind feet in standing water every so often. E.g.'s included Sisyrinchium, alliums, Alchemilla molis, Achillia 'Moonshine', Stachys and Stipa.

    Aabella - yes, staying over is something I'd like to do too. My day trip was a bit of a rush, but well worth it. West Dean has been on my must see list for ages and this was the perfect excuse to go :)

    ReplyDelete
  5. All of our stormwater stays in our garden, and in winter it can rain fiercely, twice we've had floods. But the subsequent rain gardening has coped with winter's rain.

    ReplyDelete
  6. Do you know, only recently I have realized the impact blacktop pavement has on a property. In our rural area, most folks have gravel drives but if we didn't and all of us had blacktop, we would have a great erosion problem from the rain runoff especially if it was not used in a planting scheme. This rain gardening idea is awakening all kinds of possibilities for change, big and small..am so pleased to read this.

    ReplyDelete
  7. EE - thanks for adding your practical experience. This is a topic I hope will take prominence over here very soon.

    Gardeningbren - good point. I've been thinking about what we could do about our front drive since I went on the course

    ReplyDelete
  8. Great article and useful advice, this is definitely something that I will have a look at in more depth. Thanks for sharing.

    Jason.

    ReplyDelete
  9. Thanks for a really fascinating post today VP, it's got me thinking......we already have a plan to put a huge rainwater catchment tank under our front terrace as and when we get round to sorting that area out, but there are lots of other ideas here that I could incorporate into other parts of the garden - and with all our recent rain it's pretty much a rain garden at the moment anyway!!! :)

    ReplyDelete
  10. a most interesting post! looking forward to 'seeing' the wild garden in may.

    ReplyDelete
  11. Really interesting. I hope these sorts of ideas become more mainstream, including being taken seriously on new-build projects. Definitely something I'd like to find out more about.

    ReplyDelete
  12. Very interesting. Do you think this is the likely explanation for the dozens of square/rectangularish pondy things (some with water in, plenty with none) that have appeared next to French motorways - I noticed them when we drove down to the Alps in January?

    ReplyDelete
  13. Jason - glad you enjoyed it and many thanks for the fave on Blotanical too :)

    NG - ooh I can't wait to see how you use all this info!

    Petoskystone - I'm looking forward to seeing that garden too

    Plantalscious - putting something in the building regs has to be the way forward doesn't it?

    Lu - yep, you saw SUDS. Awful aren't they?

    ReplyDelete
Related Posts Plugin for WordPress, Blogger...