Good to see that the official Priority Habitat Map for chalk streams is receiving some attention, in part in order to include additions I made to the original 1999 Environment Agency map which listed 161 chalk streams (this map was used in the State of England’s Chalk Rivers published in July 2004). My version of a revised index was published in my anthology Chalk Streams with Medlar Press in 2005 and then later – with the helpful input of Dr Haydon Bailey – in revised form in the 2014 WWF State of England’s Chalk Streams Report. That list (which isn’t exhaustive, I’m sure) ended up at about 220 named rivers.
This is the link to my 2014 index, a version of which was in the WWF report.
The new guidance says the original 1999 list did “not provide adequate coverage of small chalk streams in headwater areas, including seasonally flowing winterbournes” which are important for biodiversity and deserve protection. I agree, although in fact what the original list mostly missed was the numerous scarp-face chalk streams that rise along the spring line on the north-east facing edge of the chalk massif. It also mixed up a few of the rivers in Yorkshire listing some several times with different names (because the local convention is for the river to take the name of the parish it is flowing through) and some not at all. In addition there were a few tiny little streams here and there which were missed, probably because you’d have to fall into them to find them. All these we’re easy omissions or confusions, but being a chalk stream nerd I could see the 1999 list was incomplete in the two areas I knew really well – Dorset and Norfolk – and started working on improving it.
For my 2005 version I used OS maps and driving around the country looking off bridges. For my 2014 version I had the advantage of online satellite maps (making looking off bridges much easier and faster), a new online publication of highly detailed geological maps and a complete series of OS maps from 1946, maps which pre-dated the post-war land drainage works that can complicate things. I took the names from these OS maps where I could.
In 2014 I also, with Dr Haydon Bailey’s help, refined what we mean by chalk stream. The River Nadder – as any fule knows – is a very different river to its neighbour, the Ebble. And yet they are both considered chalk streams. In fact no chalk stream is exactly like another, but as I went through the physical differences one river to the next, Haydon was able to help me group them into geological types.
I feel we need to move away from the too vague statement “any stream or river that has a flow regime dominated by natural discharges from the chalk aquifer should be included on the map” – (which could arguably include the Thames, or Ouse?) and towards the groups of chalk stream type as proposed below, because although these ideas might need some refinement, it is a more helpful and precise way of understanding what makes a chalk stream a chalk stream and what causes their subtle differences, one river to the next. Ultimately, this grouping could well help refine restoration and conservation strategies (and designations?) by river sub-type?
When we think of a chalk stream we think of a river of a certain size – medium to small mostly, though the lower Avon is a large river that preserves it’s chalk stream character almost all the way to the estuary – that is clear-watered most of the time; that is equable in its flow patterns – ie that isn’t ‘flashy” in its response to localised rainfall, but rather has a distinctly seasonal flow regime, at its highest in spring after the winter recharge, falling away through the summer and early autumn, before building again through the winter; that flows close to bankful most of the time, with in-river weed-growth bulking up flow volumes through the summer; and with a channel form that reflects this spring-fed flow regime – wide, shallow, gravelly, stable (the cross-sectional channel shape of a river is largely determined by the ratio of high flows to low flows: the higher the ratio the more incised the channel, and so chalk streams tend not to be that deeply incised).
If you know your chalk streams you’ll know that the Itchen fits this bill to a tee, but that the Nadder veers away somewhat, is more flashy, colours after, and is immediately responsive to, localised rain and is more naturally incised. It’s still a chalk stream – by reputation and according to our definitions – but maybe more a 9 carat plated chalk-stream than 24 carat solid. The difference is all down to subtleties of geology.
What makes a chalk stream a chalk stream, what gives the stream these characteristics as outlined above, is particularly the fact that the chalk body feeding our chalk streams lies very close to the surface, and the rivers which rise from it are not much influenced by superficial surface deposits: although some are more affected than others. This particularity in turn relates to the geographical relationship between the chalk body, and the limit of the last glacial maximum and the action of the glaciers and explains why there are chalk streams in England and Normandy, but not really anywhere else, in spite of the fact that there are great plains of chalk across eastern Europe. Basically the “cleaner” the chalk body from which the stream flows (ie very thin topsoil and not much in the way of superficial geologies or layers) the “purer” the chalk stream. The influence of other geologies will take a given river away from that purest expression which is typified by, say, the upper River Itchen or Test. Given that almost all chalk streams bump into other geologies somewhere along their route, this begs the question, when is a chalk stream not, or no longer, a chalk stream?
The River Nar, for example, flows for half of its length across the Fens, but gathers hardly any extra flow throughout that lower course – a few small tributaries which are also chalky in origin – and for a large part of that lower course the channel is essentially man-made: in prehistoric times there wouldn’t have been a river so much as a freshwater segueing to salt marsh.
The Fontmell Brook, as another example, rises off the scarp slope of the downs between Blandford and Shasftesbury, and for a few hundred yards is the prettiest Lilliputian chalk stream you could imagine, but then it drops onto sandstones and Gault clay and though it is always a lovely little river, its lower course is much more incised and moody: if you looked at it near Marston and knew nothing of its origins you would never describe it as a chalk stream.
By contrast the River Nadder and its numerous headwater tributaries flow across a mosaic of chalk and also Gault formation sandstones and mudstones before it squeezes through the purely chalky hills nearer Salisbury: it gets more and more chalky the further downstream you travel.
What this suggests is that the definition of a chalk stream is not binary: it is rather a spectrum condition with a suite of characteristics which fade the more a river is influenced by other geologies and geographies than the pure chalk downs.
Anyway, this is how we grouped England’s chalk streams:
Group A comprises streams that rise directly from the chalk, flow over chalk and subsequently flow over younger Tertiary (sand and clay) deposits. This group would include the majority of the Hampshire Basin Streams and the majority of those which flow in to the Thames Basin. These tend to be the slope-face streams and are generally longer than scarp-face streams. Note that most of the iconic chalk-streams like the Itchen or Test or Kennet are in this group.
Group B comprises streams which rise beyond the chalk and subsequently flow over / through the chalk – a minority of streams but the Great Stour in Kent is a good example, rising on the Gault clay / Greensand and then flowing through the chalk. The Nadder is another example, as is the Hampshire / Wiltshire Avon and the Dorset Frome. These streams will have less equable flow regimes than Group A streams, will tend will colour after heavy rain and take longer to clear too. The flow regime makes these rivers subtly more deeply incised in the landscape than the classic Group A streams.
Group C comprises streams rising from chalk which was directly impacted by major glacial action during the Pleistocene Ice Age. This would include some northern Chiltern streams and the East Anglian, Lincolnshire and Yorkshire streams. This chalk is more compressed and fractured with higher transmissibility than further south. Group C could be further subdivided into streams which flow from chalk over glacial outwash deposits and those that flow from chalk onto older (pre-glacial) river deposits, such as the pre-glacial Bytham River which flowed eastwards from the Midlands across Norfolk and emptied into the North Sea north of Lowestoft.
Group D comprises the scarp slope streams which all tend to run for a very short distance over older (clay rich) chalk and then flow out onto the underlying Gault Clay and Greensand beds. The Fontmell Brook and Iwerne stream in Dorset are scarp-slope streams, as are the streams north of the Chilterns, the westward flowing streams in north-west Norfolk, and all the streams east of the Yorkshire Wolds.
It seems that I listed a few streams which are proving tricky to find:
My index was arranged so that you could see where a given river was on a river system. The main river is the lead name and then the tributaries are indented below it, with the uppermost tributary listed first.
So the Bassingbourne is a tributary of the River Rhee (which is easy to confuse with the Cam because both the Cam and the Rhee seem to have interchangeable names on the map) even on the latest incarnation of Apple’s “Maps” the Rhee which rises at Ashwell Springs suddenly becomes the Cam after it flows under the Northfield Road). Anyway, to the west of Bassingbourne is a street called, tellingly, Brook Road and this is the river flowing under it:
And this is the geology that it flows from and across:
The springs are quite obvious in satellite images to the south but weirdly, the river does seem to vanish into a network of drains to the north of Bassingbourne.
The Binham Stream is actually a fairly obvious tributary of the River Stiffkey, in Norfolk, that flows west from Binham towards Warham.
The Bullhill Stream is a tributary of the Allen River (the Wiltshire Allen), a tributary of the Avon: it rises east of Cranborne and flows north-east through Lower Daggons and Bullhill. To be honest, I’m not sure it counts as a chalk-stream as the geology in that area is very mixed. The Allen River that it flows into is much more unambiguously a chalk stream.
The Crichel Stream is an obvious tributary of the Dorset Allen that flows down through Moor Crichel to Crichel Lake. See the screenshot below (all screenshots thanks to the miracle of Google StreetView and used here for the public good!)
The Gowthorpe Beck is a tricky one because of that Yorkshire habit of naming rivers by the parish: it’s also called Garrowby, Awnhams and Fangfoss! It’s also tiny and probably ephemeral and it’s only chalky at the foot of the downs. It’s just north of the A166 near Bishop’s Wilton in Yorkshire. This is a picture of it from the air:
The Iwerne Stream is unmissable: its a chalk stream that flows through Iwerne Minster, the next village and chalk tributary south from the Fontmell Brook. Look for Watery Lane! See pic below.
The Melbourne is another tributary of the Rhee but you can’t miss it if you find the village of Melbourne. It’s also called the Mel, so that can be confusing. See pic below.
The Otby Beck is another tricky to find, ambiguously named scarp-face chalk stream, tributary of the Ancholme, just north of Walesby, the next scarp-face stream north of the Rase in Market Rasen. Here’s a picture of it under Park Road on the way from the A46 to Claxby Park.
The River Chalgrove is easier to find. Just look for Chalgrove in Oxfordshire. It is made up of three small, scarp-face tributaries that rise in Lewknor, Shirburn and Watlington.
The Wyn is the next tributary downstream from the Tadnoll on the Dorset Frome. It flows over a mixed geology from Winfrith Newburgh and downstream, but it rises on the chalk near Chaldon Herring.
The Walsham is a tributary of the Little Ouse that rises at Walsham Le Willows in Norfolk. It flows over a very mixed geology that includes chalk, but it may well not quite count as a chalk stream. It is incised and clearly ephemeral, but has some nice meander patterns here and there.
The West Compton Stream is a tributary of the Frome, rising in the chalk hills of West Compton (south west of Wynford eagle and Maiden Newton) and looks like this:
The Wraxall Brook is also a headwater tributary of the River Frome, rising in the chalk, mudstone and sandstone formations of west Dorset near Rampisham. Although it flows over a fairly mixed geology it is definitely a chalk-stream and it picks up dozens of chalk springs along its route. See pic below.
The Beachamwell Stream is hard to find but it is a tributary of the Wissey, the next chalk tributary downstream from the Gadder which flows past Oxborough Hall. A lovely little chalk stream, it rises just south of Beachamwell and flows south west under the Gooderstone and Eastmoor Roads. See pic below.
I can’t find a Bishop Stream in my index, but there is Fonthill Bishop Stream, a tributary of the Nadder in Wiltshire which is very easy to find if you look for Fonthill Bishop. There is also a Bishop’s Wilton Beck, which is also easy to find if you look for Bishop’s Wilton in Yorkshire. It is small, I have to admit, as you can see:
The Charlton Marshall Stream is very hard to find. It is a tributary of the Stour near Charlton Marshall, in Dorset and by reputation was once an important salmon spawning stream for the main river. It is only a few hundred yards long, rising at the foot of the downs to the west of Spetisbury CE Primary School. I have a good photo of it somewhere as I go fishing near there every year. I’ll try to find it.
It was really only the name which made me think the Fulbourne must be a bourne. It is clearly ephemeral as the images on google maps show a dry stream bed, but the surrounding geology is definitely chalk. It is a tributary of the Quy water and rises in Fulbourne just to the east of Cambridge.
The Gussage Stream is another tributary of the Dorset Allen. It flows from Cashmoor through Gussage St Michael and Gussage All Saints. You can’t miss it really.
The Kneeswell Stream, by contrast, is very, very hard to find. It’s near the Bassinbourn (see above), rising from springs at the base of the the same low chalk hills in Cambridgeshire, in the village of Kneesworth.
The North Bourn is a tributary of the Great Stour in Kent. Look for Northbourne near Shoulden. It’s chalk springs feed a veritable maze of lowland dykes but if ever there was a site for the restoration of this type of minor chalk stream it is here. In the picture below you can see the original river flowing through a drained field, with the ditches that now cary the water to either side. If the locals want to restore this, I’d be happy to help!
The Pakenham Fen is another chalk derived, fen-like river (perhaps we need a category of chalk stream that captures these rivers as there are lots of them) which rises near the Walsham (see above) flowing through Pakenham to Ixworth and into the Black Bourn and then the Little Ouse, in south Norfolk. See pic below.
The River Shep is a tributary of the Rhee (also called the Cam, but not THE Cam!). It flows through Shepreth. See pic below.
The Sapiston Brook is also known as the Blackbourn and it is the river into which the Walsham and the Pakenham Fen flow. It then flows into the Little Ouse. See pic below.
The West and East Hendreds, also called the Lockinge, are scarp face tributaries of the Thames that rise at East Lockinge West Ginge and East Hendred to the east of Wantage. See pic below.
Finally, the Whitewool Stream is a tributary of the Mean that flows through the Mean Springs fishery from just north of Coombe.