On the Bing imagery within JOSM and (sacrilege!) Google maps (make sure that ‘Earth’ is enabled) you can find a Flood Lagoon nestled amongst all the Nottingham houses in Carlton, Nottingham NG4. The problem is that OSM does not have a “man_made:flood_lagoon” key/value, so I cannot show it to you on the OSM map (I made up what seemed to me to be the closest to what it should be but, of course, openstreetmap.org will neither store it nor show it).

Discovery:

I was surveying the even numbers on Foxhill Road Central on Monday 20 June when I came across a kiddie’s playground at the corner-junction of Foxhill & Carnarvon Grove. See if you can spot in this picture the single sign of this flood lagoon (hint: it is the locked-gate entry to a narrow strip of grass + workman’s hut at the back of the playground):—

My spider senses were tingling, but none of the locals that I asked knew what the hut was for.

Whilst entering Foxhill Road houses on to the OSM Map the next day I came across the Flood Lagoon on Bing, and very mysterious it looked indeed. I contacted Severn Trent & explained what I was doing & asked what on earth it was. She got out her own map & it was then that I discovered that it was “Flood Lagoon 5805”. I put it up on OSM, even though I knew that I was just wasting my time.

Yesterday (Thursday 23 June) I returned to survey the odd numbers on Foxhill. This time I was determined to see if I could get a photo of the lagoon. Fortunately for me there turned out to be a clear view of the lagoon from Radcliffe Gardens at the rear of Foxhill Road. I took a number of photos; unfortunately, I was also testing a new camera app on my phone, and some of them have simply vanished into the void. Two frames are left:—

Coda 1:

Thanks to some fast comments I’ve been able to find a tag documented on the OSM wiki (Tag:landuse=basin) that least allows me to show it to you on the map: Flood Lagoon 5805. That provides a viewable-outline in JOSM. Sadly, no outline in ordinary circumstances in osm.org, although the name can be searched for (“5805” could not be found previously).

Coda 2:

(Sunday 26 June)
…and now I am mighty confused. Flood Lagoon 5805 is identical in OSM to what was there before, but now shows on the map as a blue-infilled area. Is this due to some caching-issue on the server, or has there been an update in the tile-server?

Coda 3:

(Monday 27 June)
Carlton Foxhill Road Central Flood Prevention Lagoon:
(a flood prevention lagoon operated by Severn Trent) (contained within the area 426553952)

Sluice Valve 5805 (at the Pitch Close end) empties surface water from the Fairway Drive estate into the concrete channel of the lagoon. Water run-off can come from both playing pitches to the north-west of the Sports Centre and also from allotments to the north of the estate. The course of the concrete channel follows that of a stream which formerly ran here prior to development in the early part of the 20th Century (all such streams are now culverted).

Sluice Valve 6714 (at the Playground end) empties all contained water into the Carlton Foxhill Road Central CSO. That culvert (as long as I recall this information correctly, from an engineer that called me today) ends outside the Old Volunteer Pub on Burton Road.

The land surrounding the concrete channel between the 2 sluices has been graded into a deep basin to temporarily contain exceptional volumes of water during storm conditions.

Note: Severn Trent does NOT give this lagoon any name; I have therefore assigned it a sensible name for search purposes. Many thanks to Philip & others at Severn Trent for patience & explanations.