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 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.
Where is It?
The Upper Lye can be defined as the area (purple) between Old Road, Girdlestone Road (off The Slade), The Slade and a line approximating to Dynham Place going north.
The overview above shows:
- The general outline of the Lye (red) – note the small gully going to the junction of Girdlestone Road and The Slade, now mostly buried by the “playground” although a remaining part is visible from the allotment path near The Slade entrance.
- The 10 house Warren Crescent Development and 2 Dynham Place (yellow)
- The Lye SSSI (green) and Local Nature Reserve is up valley (not shown)
- A set of wells (Yellow – Wells 1-5)
Why Does It Matter?
It 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 either falls directly in the Upper Lye or flows underground into and along it – even now, wells exist at the base of the the Town Furze allotments which are themselves very probably on made ground.
The unique Ice Age relict flora of the Lye Valley depends on not only water, but alkaline groundwater mineralised from flowing through calcareous rock layers, recharged continually by rainwater falling on vegetation.
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 (See Warren Crescent – A Study In Shame ) and 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
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.
See also Ellie The Elk On The Lye for a more light-hearted introduction.
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.
The Upper Lye – The “Discovery”
What I did “discover” was the secret valley of the Upper Lye where sloping gardens take a long, long stretch backwards, 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 Development Site
The following images show the 2 Dynham Place development site looking from Girdlestone Road.
Note that not only is the steep bank to the left Girdlestone Road causeway made ground but much of the site below is also as shown by the ground condition report.
Below shows the clear shape of the west side of valley 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.
The Upper Lye Explained
The valley gardens slope steeply down from Old Road and from each side of the valley leading down to an apparent streambed, which subsequently drops gently down to the Lye until approximately 2 Dynham Place (2DP purple) where the valley widens and falls substantially into the main Lye valley.
The detailed view 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 at 95.4m at both sides as marked, indicating made ground at this point of 4m (95.4m-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
- Red arrows showing slope direction
- A point T (Top) (centre) at which the streambed becomes clearly defined from the steep slope from Old Road and a clear rather flat V valley forms
- The old streambed as blue (no surface water)
- The proposed 2 Dynham Place development in purple (2DP), ON the streambed and underground flows
- A development (Purple 195) (14/02481/FUL) replacing a building subsequent to an enforcement notice ON the streambed
- SW1 and SW2 stormwater drains (blue)
- 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
In addition, the last remnants of a probable Roman way still exist shown as “Fmr Way” in brown (top left). (see forthcoming article “The Roman Lye”)
The Girdlestone 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 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 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:
This means the true extent of the valley, and it 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 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
So, in effect, this large and important part of the Lye Valley as been effaced from our consciousness.
Where Is The Stream Now?
Every householder I asked 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 The Slade were built and drains (SW1,SW2 above) 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.
Old Road, and in particular, The very built up Slade 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 (2 Dynham Place boreholes) with very slow moving water, emerging into the main Lye valley and fen with a very large bell mouth.
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 swamp, to meet Old Road clinging to the Upper Lye western valley side. (See forthcoming article – The Roman Lye)
The Slade road is running 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, further blocking groundwater and disguising the original Valley shape which would have been similar, but slightly steeper, than the slope of Old Road observable by looking up from The Slade/Old Road junction.
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.
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 (see articles above)
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 continued beyond Old Road.
East, the land rises steadily from 99m to approximately 109m at the A40/Old Road crossing, where beyond, Shotover rises steeply – the original contribution from here is unknown, but believed to be now zero. West, the land rises from the base of the Upper Lye valley to Girdlestone Road (North/South) before falling towards Oxford.
Permeable rock layers slope slightly from the NE to SW in the vicinity of Warren Crescent, and E/SE in the rest of the catchment, so the land surface AOD (height) is not the only factor.
The Thames Water 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 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.
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%) [a] 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% 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
[a] This is based on the percentage of impermeable surfaces in the Thames Water catchment it is similar for the natural catchment.
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
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
 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)
 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)”
 As above – Lye Valley Brook SSSI – Modelling Report v2.0, Appendix A Modelled Network (Drains)
Town Furze Map, 1954 (Under Oxford City Planning Portal Search: “Town Furze”)
Oxford Planning Portal, Applications Map for AOD points
 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)
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Version 0.3 – 04/07/20
Version 0.4 – 09/07/20 (2 DP photos added)