[Talk-GB] SuDS (Sustainable Urban Drainage Systems)

[SK53]

Last night before visiting the pub we had a look at part of Sheffield's
"Grey-to-Green" SuDS system. Unfortunately all my batteries ad packed up at
this point, but there are some decent pictures on twitter
<https://twitter.com/NigelDunnett/status/1136347921950134273>.
The bit we looked at was outside the courthouses. It consisted of :

   - A bio-swale. Planted with a colourful mixture of plants most of which
   I've forgotten now, although I do recall Jerusalem Sage. The ground was a
   gravel mix with presumably a geo-membrane underneath to retain water. A few
   birches were also planted along the length of the swale. Superficially this
   just looks from a distance like a large ornamental flower bed.
   - Concrete 'dams' periodically, along the swale, rising to within a few
   inches of pavement level and with a v-shaped notch in the centre. Obviously
   these are not really dams, more a type of weir, being designed to moderate
   the flow of water through pooling behind each dam. I've seen similar
   constructions in the Alps albeit on a larger scale.
   - At the bottom of the swale a more obvious drainage channel. Where the
   swale is broken for pedestrian access this runs in a recessed gutter
   covered by a grille.

There are probably other features of the completed scheme which we didn't
see. I notice many new-build housing estates will have an area set aside as
a water retention basin.

I've previously noted a SuDS along Ribblesdale Road
<https://web.archive.org/web/20131002214536/http://www.susdrain.org/case-studies/case_studies/nottingham_green_streets_retrofit_rain_garden_project.html>
in Nottingham, but the features involved are on too small a scale to
consider mapping for now.

This type of infrastructure is becoming much more popular, particularly
with extreme flooding events due to surface run-off. I'd hoped to look at
the one in Sheffield, and fortunately Laura both remembered this and where
it was. Larger ones are relatively simple to map the main features,
choosing viable & appropriate tags is more challenging. I've had a go
<https://www.openstreetmap.org/#map=19/53.38533/-1.46791>, but am very open
to other suggestions. I suspect the whole swale should be mapped as a
waterway feature. For now I've used waterway=drain with intermittent=yes
for the channel in the swale & the connecting part of the drain running in
a covered gutter (one import in Santa Clara Co, CA opted for
waterway=stream). However many of the features could use man-made rather
than waterway tags.

In conclusion: there's probably a SuDS near you; they're hard to tag (for
know); but not too hard to map; we could do with thinking about better tags.

Regards,

Jerry
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