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.
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.
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 :)
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:
- Rain Gardens - A how-to manual for homeowners (pictured)
- A Guide to Stormwater Best Management Practices (Chicago)
- Rain Gardens and Bio-Infiltration (by Nigel Dunnett) - I couldn't find this, but the 2 page handout cites Artful Rainwater Design as a useful web resource
- I couldn't find the Bioretention fact sheet handout from Oregon's Metro website, but I did find Portland's Sustainable Stormwater Management and the USA's Green Building Council websites along the way
- Facts About Stormwater Conservation in Your Backyard (Maryland)