The Upper Lye – Headington’s Secret Garden
Introduction
Many times visiting the Lye Valley I have thought “what a wonderful special place” but was left puzzled by one unexplained absence – where exactly was the source of the Lye Brook? All that was visible was a culvert and drains, even the most in-depth hydrology report[1] made no reference to it.
Some speak in awe of the search for the source of the Nile, some will remember Malchair’s great Porck Griskin expedition to the wilds of “Heddington” of 23 Mar 1771 – and following the footsteps of those intrepid explorers of yore, Headington Heritage plunged into deepest dark-greenest Headington, and, in keeping with long tradition of expeditions past, “discovered” what the locals were perfectly well aware of already.
This June 2021 version adds new evidence after a COVID-19 pause, of the probable hydrological connection with Rock Edge meaning this area is more important than realised.
Appeal
Please Join Friends Of Lye Valley (FOLV) to help save this precious place:
Web: http://www.friendsoflyevalley.org.uk
email: friendsoflyevalley@yahoo.co.uk
Where Is The Upper Lye Valley?
The Upper Lye can be defined as the area (purple) between Old Road, Girdlestone Road (off The Slade), forming very probably a direct hydrological connection with Rock Edge SSSI and Local Nature Reserve.
The overview above shows:
- The outline of the Upper Lye (Purple)
- The general outline of the Lye Valley (Red)
- The Lye Valley SSSI (north) (Green) with West and East Fens
- A set of wells (Yellow pins – Wells 1-5) at the base of the Upper Lye
- The 10 house Warren Crescent and 2 Dynham Place developments (Yellow)
Why Does It Matter?
The unique Ice Age relict flora of the Lye Valley depends on alkaline groundwater mineralised from flowing through calcareous rock layers, recharged continually by rainwater falling on vegetation and slowly infiltrating into the ground.
The hitherto almost unknown Upper Lye Valley makes a very important, and hitherto little understood, water contribution to the main Lye Valley, Oxford’s natural crown jewel, of which it forms an integral part.
Much of the rainwater in the Lye catchment, particularly important for the West Fen either falls directly in the Upper Lye valley or flows underground into and along it – even now, wells exist at the base of the the Town Furze allotments although the springs are buried under deep made ground.
The Upper Lye almost certainly acts as a conduit for water from the outer areas of the catchment, underlain with a narrow band of limestone providing calcified groundwater to the Lye SSSI, the west fen in particular.
The Lye is under siege, its natural catchment groundwater reduced by overdevelopment and water redirection into town drains – it simply cannot survive any further negative changes.
Oxford City Council is knowingly and recklessly gravely endangering this precious place with two developments – a pending 10 house development (approved) at Warren Meadow for which the Council, by its own admission, has not done a hydrological survey to understand the effects on the flows below of many thousands of tons of foundations directly above
For more details see articles The Warren Crescent Housing Development – Risky, Reckless and Ruthless and Warren Crescent – A Study In Shame ) [EN1]
More recently, a development at 2 Dynham Place which will require 10m deep foundations directly over the Upper Lye streambed and its underground flows which remains unapproved at time of writing. The Lye Fen – Another Death Blow
The Upper Lye – An Overview
Valley gardens slope steeply down from Old Road from the north, and from the Town Furze Estate to the west, and The Slade from the east, to the dry streambed (blue) at the base.
From the north, the valley widens and drops gently down to approximately 2 Dynham Place (2DP purple) where the valley widens and falls substantially at Girdlestone Road into the main Lye valley.
The detailed bird’s eye view above shows:
- A height drop of 98.8m from Old Road to the ORIGINAL height of 2 Dynham Place land at 91.4m a drop of approximately 7.4m
- The current height of Girdlestone Road causeway at 95.4m at both sides as marked, indicating made ground of 4m at this point as the natural surface is 91.4m
- Brown where the sloping ground forms a distinct valley, with valley sides from both east and west, forming a classical riverine V shape
- Light blue arrows showing slope/surface flow direction
- The dry streambed route as blue
- A point T at the base of 205, The Slade garden at which the streambed becomes clearly defined from the steep slope from Old Road and a clear rather flat V valley forms southward
- A streambed going NW of T to where a well was reported in the garden of number 80, The Slade
- A streambed going NE of T to the junction of Old Road/Windmill Road/The Slade
- A bog (blue) that existed at 4 Dynham Place and a pond that forms after heavy rain regularly at the development site
- The photo direction of the photo of the allotments in yellow below
- The proposed 2 Dynham Place development in purple (2DP), ON the streambed and underground flows (see also [FN1])
The Upper Lye – The “Discovery”
What I “discovered” was the secret valley of the Upper Lye where gardens take a long, long stretch backwards from their houses on either side of the valley to a base approximating to the rear fences – some unkempt and wild, a haven for wildlife including deer, including one flanked by a line of 200 plus year old beech trees striding purposefully down valley and a mini wood providing a haven for wildlife, others neatly manicured, others yet still sporting field gates.
The Girdlestone Road Causeway
When the Town Furze estate was built in the 1950s, the mouth of the Upper Lye was blocked up with the Girdlestone Road causeway running from The Slade to approximately 4 metres above the natural surface at 2 Dynham Place.
The below photo shows the extent of the made ground at Girdlestone Road looking from the base of the Town Furze allotments to the north.
The made ground of the causeway is shown in red, however the allotments shown and the camera position are also on Made Ground.
In addition, most of the area to the immediate north and south was covered in earth forming Made Ground of varying depths:
The Development Site – 2 Dynham Place
The following images show the 2 Dynham Place development site looking from Girdlestone Road.
The steep bank to the left is part of the Girdlestone Road causeway is made ground, as the flat grassland at its base, as indicated in the ground condition report.7]
Below shows the clear shape of the west side of valley (left) looking north over the development site from Girdlestone Road, much of this is Made Ground. The streambed is just beyond the extreme right of the picture.
Below shows the depth of the ground at 2 Dynham Place even following made ground infill, which is a further 1.5-2m depth.
How the Upper Lye Was Hidden
The above meant the true extent of the valley, and its contribution to the Lye hydrology, has not hitherto been understood as:
- The valley is more clearly defined at the northern (Old Road) end due to the higher surrounding ground but is largely hidden from public view
- Very substantial infilling[7] to create Made Ground as part of the Town Furze Estate development meant the valley appeared less significant than it is
- The creation of the Girdlestone Road Causeway filling the entire valley mouth which extended in a shallow V shape from The Slade to approximately the current Dynham Place
- The allotments and sides above are also of Made Ground
So, in effect, this large and important part of the Lye Valley has been effaced from our consciousness.
The Streambed Route – The Evidence
Moving north from Girdlestone Road, and the 2 Dynham Place development site, the Upper Lye streambed (blue) is clearly defined from the allotments up to the point T on the bird’s eye image above, running approximately on the rear fence line at the base of the valley of the back to back properties – finally disappearing in the garden of 205 The Slade.
From point T (base of 205), it turns north east (right diagonal) to the Windmill Road/Slade/Old Road junction as:
- The line of higher ground to the immediate west of the streambed, shown on Lidar below, is wide at Girdlestone Road, shrinking gradually to 205. A small gully runs across and up and across 205’s garden, which is flat at its base
- A faint streambed runs along the fence line between 86 (east fence) and 88 Old Road (west fence), in an undeveloped block of land that originally was 88’s rear garden. Garden steps, a low retaining wall, and possible well are visible.
- This fence line is slightly sloping upwards towards the Old Road junction, in sharp contrast to the steep west fence at 86 Old Road, ie the lowest point is the 86/88 fence line with 86 Old Road being the other side of the valley
- The junction is the lower than land to the:
- West which drops from the Girdlestone Road (North/South)/Old Road junction (100m),
- East – Old Road down from Shotover
- North down from a clear rise opposite the Nuffield Centre main entrance – ie it is valley floor
- The alignment of Old Road itself, which runs as it does to avoid the “Slaed” or wet valley of the Upper Lye, this being the first feasible crossing point
- The prior presence of a windmill at point B may point to a water source
- The natural dip at the junction is hidden by its construction. Made ground to 2’3″ (0.7m) at point B on Lidar below (BGS SP50NW265, 10m resolution) indicates this could be deep
The alignment of the Rock Edge gullies below (top right) may indicate hydraulic action – although this is quarried this may have been due to already exposed rock, there is a clear height differential from east down to west at Rock Edge, and a slight one from south to north, with Rock Edge road running along the lowest part at the Old Road junction.
Where Is The Stream Now?
Every householder said there had been a stream there, but none could offer any evidence.
Very probably it disappeared soon after development in the 1920s and 1930s when the houses along Old Road and The Slade were built and drains running down them diverted much of the water directly into the Lye, possibly still seen as a health hazard back in the days when incurable pandemics still raged.
Further, Old Road, and in particular, The very built up Slade Road create a damming effect and barrier to water ingress into the Upper Lye valley and thence to the fen.
A series of wells (Yellow pins Well 1-6 above) still exist at the base of the Town Furze Allotments below Girdlestone Road indicating continued underground flows.
What Did The Upper Lye Look Like?
It was peat bog and fen[7] with very slow moving water, emerging into the main Lye valley and fen with a large bell mouth at modern Girdlestone Road and below, this in effect created hydrostatic pressure enabling the surrounding limestone to be saturated with groundwater which then emerges in the west fen.
An indication that it was a considerable barrier to communication is the route of former, possibly Roman way starting at the south-west end of the Churchill Hospital site, running along the western edge of the Lye Valley, turns sharply north at modern Dynham Place to avoid the fen and slopes, to meet Old Road clinging to the Upper Lye western valley side. (See Headington’s Great Roman Pottery on the Lye)
The Slade road runs north-south on the east side of the valley (similar to the “Roman” way on the west side), and is named from the land it runs over. The “Old English root word “slaed” – meaning land in a (marshy) valley (Field, 1972, 206) (See Definition Source ), or small valley, or “A valley, dell, or dingle; an open space between banks or woods; a forest glade; a strip of greensward or of boggy land” ( Headington History – The Slade) – are clear indications that the area was originally a marshy valley along which The Slade road now runs, ie over the ground in the Upper Lye valley.
The ground naturally slopes down from the East (Wood Farm) mostly at right angles to the Upper Lye Valley. The current Slade road is built up particularly near Old Road, disguising the original Valley shape.
The main Lye valley was fen with gently sloping sides, the Lye Brook little more than a leak at end of a fen pond than even a stream, see The Lye – Taunt In Colour for an understanding of what the Lye used to look like.
Why The Upper Lye Runs Due North
The below shows the British Geological Survey (BGS) map for the area – this is very small scale, and shows only an overview – each point will have many rock strata.
The very noticeable shape of the Lye valley, moving SW to NE as far as Girdlestone Road and then turning north as the Upper Lye at Girdlestone Road can be explained as below with reference to the BGS map above:
- Water falls on the high ground to the east on Shotover
- Kimmeridge(dark orange) and Amphill(yellow) clays are impermeable, so water flows west below ground arriving at the limestone band (pink) (eg: to red dot at Rock Edge)
- The groundwater within the Lye catchment (limestone part red border) then dissolves the limestone, becomes calcified, and creates the Upper Lye valley parallel to the impermeable N-S Amphill Clay band
- Water flows down the Upper Lye valley (from red dot of Rock Edge south), originally into a fen – some water would then seep into the valley sides as groundwater
- The underlying rock strata slope NE->SW (Lamberth 2007), so groundwater emerges at the west upper side of the main Lye valley feeding the fen (green)
- Some fen water and some would emerge as a small stream in the area of Girdlestone Road as evinced by the wells at the allotments.
This explains the northern hook of the Upper Lye valley, as water can only flow downwards once it emerges from the impermeable clay layers to the east, therefore the Upper Lye runs parallel to the edge of the north-south aligned Amphill clay Strata (Yellow).
It is of note that Rock Edge is the closest to the Amphill Clay band. There is a very small narrow band of Limestone from the Amphill Clay edge to the Lye Valley SSSI for groundwater to be calcified.
Interactive Catchment Maps
This map gives a easy overview of the Lye Valley catchments:
A more complex view showing all catchments:
The Natural Catchment
The Lye’s natural hydrology is for rainwater to fall in its natural catchment area (blue below), flow underground, charging the aquifers, very slowly picking up minerals, before wetting the Lye Fen, either from a slowly trickling Lye Brook, or mostly from the perched water table directly above the fens which are now under imminent threat of destruction.
North, beyond Old Road (99m) the land rises to 104m at approximately Old High Street Waitrose entrance before falling down to Bayswater Brook and the A40 ring road, however a small ridge near the Nuffield Centre entrance demarcates the limit of the catchment slightly north of Old Road, followed by a significant dip to the north. Possibly groundwater flowing in this dip finds its way in to the Upper Lye valley which continues beyond Old Road.
The Thames Stormwater Catchment
Urbanisation and the artificially large catchment (orange below) formed by Thames Water storm drains discharging into the head of the Lye Brook is shown below.
The natural catchment (blue) as estimated by Curt Lamberth and revised by Judy Webb is approximately 73HA BUT it already excludes an area east of the ring road.
Thames Water[2] has calculated the catchment as ORIGINALLY at 73HA but now EXCLUDING an area east of the the eastern bypass (A4142) due to the road at only 65HA. (TW p.16) now.
The discrepancy between these two figures is to be expected due to the difficulty of estimating on very gently sloping and now very disturbed land and poorly understood underlying geology – no groundwater catchment map has been provided by Thames Water.
Of the 65 HA groundwater catchment, only 50 HA is not lost to stormwater drainage (from impermeable surfaces such as roads and rooves), the effective groundwater catchment is a reduction of 32% (73HA–>50 H A) or 68% of the original flows.[2]
Alternatively, applying a 37% impermeable area (which is more realistic given developments since 2011) this is ((65HA * 0.67)=41 HA=41/73HA or 56% remaining flow.
In addition to this, very substantial ground disturbance and crushing of underlying layers from foundations, causeways has blocked many of these flows even further.
The developments at Warren Crescent Meadow and 2 Dynham Place are at exactly the most damaging places, the first blocking the underground flows just before they reach the springs above the perched western fen, the second directly above the streambed of the Upper Lye at its base.
What This Means For the Lye
- Groundwater (calcareous) is very substantially decreased to 68% of the original, or just over half original flow (56%) extrapolating to 2020 conditions
- Rain falling in both the natural (blue) and Thames Water (orange) catchments on impermeable surfaces (roads, rooves etc) goes directly into the storm drains (37%) [FN1] discharging into the head of the Lye valley delivering non-calcareous, polluted water to the Brook, scouring it especially in storm conditions – originally storm water would be mostly attenuated by vegetation and become groundwater
- The Lye brook streambed is therefore scoured by very large and variable flows (storms) meaning water goes under and by the fen, not through it and is therefore lost – this is approximately 37%[2] of the combined catchments
- Roads, in particular Old Road, The Slade and the bypass have created effective dams to natural flows, further reducing groundwater flows
[FN1] This is based on the percentage of impermeable surfaces in the Thames Water catchment it is similar for the natural catchment.
Conclusion
The Lye is on life support, surviving on a much depleted groundwater supply, subjected to relentless attack by Oxford City Council, with ill-thought out and reckless developments and no catchment management plan. See The Lye – Taunt In Colour to understand how much has already been lost.
The recent Local Plan did not even have a background paper submitted for the Lye Valley SSSIs (North and South), and went no further adding a reference to it to specific site policies that may impact it, and made reference to construction buffer zones which are irrelevant in relation to hydrological risks.
At a minimum the Council must:
- Stop work on the disastrous Warren Crescent 10 house development which may well block all flows to the west fen
- Refuse permission for the 2 Dynham Place development as it will severely impair all flows from the Upper Lye and surrounding area
- Define groundwater protection zones in which further development is banned or restricted as per the Lamberth Report recommendations [1 p.39]
- Review Thames Water network for opportunities to redirect, redesign or attenuate the drain network
Acknowledgements
Very many thanks to the residents of the Upper Lye area who were kind enough to let me see their gardens, and constant guidance and information from Judy Webb and others, and Stephanie Jenkins and her formidable Headington History Web Site
References
[1] Investigation of the possible hydrological effects on the Lye Valley Sites of Special Scientific Interest and the riparian zones of the Lye and Boundary Brooks as a result of development on Southfield Golf Course, A pre-EIA assessment,October 2007, Dr Curt Lamberth (Prepared for Oxford City Council)
[2] The figures given in this section are from information provided by Judy Webb who referenced “Thames Water Utilities Limited Lye Valley Brook SSSI Catchment Investigation, Final Report RT/EWI/CH11/216/01.00 41518877 February 2012 (Prepared for Natural England)”
[3] As above – Lye Valley Brook SSSI – Modelling Report v2.0, Appendix A Modelled Network (Drains)
[5]Town Furze Map, 1954 (Under Oxford City Planning Portal Search: “Town Furze”)
[6]Oxford Planning Portal, Applications Map for AOD points
[7] 20/00463/FUL | Erection of 2 x 3-bed semi-detached dwellinghouses (Use Class C3). Provision of bin and cycle storage and alterations to landscaping. | 2 Dynham Place Oxford Oxfordshire OX3 7NL (Ground Condition Report)
Author
Mark
Headington Heritage, A personal blog
Visit : www.headingtonheritage.org.uk
Email: headingheritage@outlook.com
Follow me on Twitter: @headingheritage
Version 0.3 – 04/07/20
Version 0.4 – 09/07/20 (2 DP photos added)
Version 1.0 – 09/06/21 (Rock Edge connection following further research, links to maps)
Endnotes
[FN1] In an earlier development, the Council approved (14/02481/FUL) a house sized described as a meeting centre replacing an equivalent structure, which was subject to an enforcement notice, directly on the Upper Lye streambed – although the officer noted the 2.5m drop of the streambed, he failed to understand its significance.
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