Hydrological and Drainage Report Response
Oxford City Council intends to build 2 houses across the Lye Valley, at this point naturally 5-6m deep, in the rear garden of 2 Dynham Place (almost opposite the Girdlestone Road playground) – this will create an underground dam of 18m * 7m * 10m deep PILE foundations, blocking the flows and rupturing the perched water table the North Fen SSSI depends on for its very survival – this is madness.
This extraordinarily reckless act of environmental vandalism has been endorsed by a recently submitted hydrological and drainage report in three parts available as below PLEASE OBJECT.
This article is a response to this truly AWFUL report – both are probably a good cure for insomnia being rather technical. Even if you have already objected, please object again before Thursday October 6th 2020 5PM.
The author has no hydrological qualifications and expresses a personal opinion only.
The Report in three parts is available from the http://www.oxford.gov.uk/planning under 20/00463/FUL as below – note this is a NEW chance to object so please object to the report even if you already have to the original planning application.
PLEASE spend 5 minutes objecting either using the link above or mail to firstname.lastname@example.org
REF: 20/00463/FUL | Erection of 2 x 3-bed semi-detached dwelling houses (Use Class C3). Provision of bin and cycle storage and alterations to landscaping. | 2 Dynham Place Oxford Oxfordshire OX3 7NL
Citing the Key Objections below and any others.
Please Join Friends Of Lye Valley (FOLV) to help save this precious place from Oxford City Council:
The report seems to NOT to have:
- Reviewed all evidence, but misinterpreted the data, clearly stating it was supporting the application or correctly used evidence from the Lamberth report, arriving at opposite conclusions
- Addressed any of the objections it purported to address
- Been even aware that the site is IN the Lye Valley streambed
- Any understanding of the groundwater catchment flows upstream of the development and that it is a pinchpoint critical to the West Fen
- Understood the requirement is to show no adverse effects on groundwater NOT mitigate as per Local Plan RE4
The only function of this report was to produce a Hydrological Impact Assessment by interpretation of the evidence already provided and present a surface water solution.
Other than the correctly identifying the address of the property, scarcely a single assertion seems correct – this appears to be a catalogue of errors, misunderstandings with misinterpreted, or unevaluated, evidence –the report seems of extraordinarily poor quality.
- Oxford City Council have employed the same company (or successor) whose flawed advice led to the grant of planning permission for Warren Meadow
- The Upper Lye Valley is key to the hydrology of the West Fen
- The proposal will severely impact approximately 63% of the groundwater catchment of the West Fen
- Pile foundations will effectively form a dam impeding flows BUT also causing water loss by puncturing the layer the water table is on, creating a water path to below the Lye, causing a loss of water gradient and hydrostatic pressure causing irreversible harm to the SSSI
- The heavy trench and deep drainage structure will further block the flows
- The onus of proof is on the developer to prove an assessment can demonstrate that there will be no adverse impact on the surface and groundwater flow to the Lye Valley SSSI.(RE4) The evidence proves precisely the opposite.
- The Upper Lye is a key part of the hydrology of the fen as described below
- The Lye Valley Fens (SSSIs) are on life support, having lost much of their groundwater supply due to overdevelopment and excessive flows due to Thames Water drains leading to scouring – NO further loss is allowable
|2DP||2 Dynham Place – The Development Site|
|Stantec||2 Dynham Place, Hydrological Impact Assessment, Surface Water Management and Maintenance Plan, Project Ref: 45340/5003 | Rev: – | Date: August 2020|
|GIS||Ground Investigation Services March 2019 Report No. S.5304|
|WSP||Oxford City Housing Limited, LAND EAST OF WARREN CRESCENT, Baseline Hydrogeological Monitoring Report, FEBRARY 2019, WSP|
|BGS||British Geological Survey, 1973|
|Lamberth||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, Oct 2007, Dr Curt Lamberth.|
|HH||Original article on the Upper Lye explaining the Upper Lye Valley in relation to this Site: https://headingtonheritage.wordpress.com/the-upper-lye-the-secret-garden/|
|MWH||Thames Water stormwater catchment from MWH Global report to TW, 2011; via Dr Judy Webb|
|TFM||Town Furze Map 1954 – Original Plan and topology of Town Furze (Warren Crescent etc) estate – Oxford City Council (Planning Portal)|
|SSSI||Site of Special Scientific Interest – Refers to the North Fen (with West and East Fens on either side of the Lye Brook) or Lye Valley North SSSI Unit 1 unless specifically stated|
Oxford City Council has a clear conflict of interest as both the applicant and arbiter. This statement indicating support gives rise to a perception of partiality:
This report has been prepared by Stantec, to support the planning application for 2 Dynham Place, application reference 20/00463/FUL. Planning approval is being sort for the formation of a 2 new properties at 2, Dynham Place, Oxford. (Ref: STANTEC)
A very specific request was made NOT to engage Stantec (former PBA – Peter Brett and Associates) in order to receive a fresh, third party view following apparently factual misunderstandings in the Warren Meadow report which seem to have been replicated here.
It is beggars belief that the Council sees fit to engage a company that advised that the West Fen (13/01555/CT3) was a “southern area of cleared reeds”, as it was not the “principal fen” although 40% of the whole North Fen SSSI, further stating any contribution from the groundwater passing under the development would not be relevant as the brook was incised anyway!
The SSSI was defined for its environment (flora, calcareous springs) the degraded state was a justification to remediate the streambed, stormwater drains, and West Fen, not build 10 houses with a wholly untested, uncalibrated SUDS system delivering water in the wrong place.
These seem to be elementary errors, which have led to the unfolding disaster at Warren Crescent.
The stated objective of the report is to address the concerns of the FOLV:
1.1.6 Concern has been raised by Natural England and Friends of the Lye Valley as to the impact that the development will have on the surface water and groundwater discharged from the site, serving the Lye Valley, a local Site of Special Scientific Interest (SSSI). For this reason, a Hydrological Impact Assessment has been undertaken. (Ref: STANTEC)
WRONG – Many other concerns were raised as below of which site discharge was only one.
The overall situation of the 2 Dynham Place (2DP) development is shown below:
- 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
- Light Blue arrows showing slope direction and flows
- 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
- 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
 Groundwater flows will be same except for the small area to the west of the streambed where water will flow down and continue from the NE (see below)
With reference to this image from 1953:
The form of the valley and the streambed can be clearly seen although this was already partially Made Ground. – You need to zoom in (create account for best view), looking for the roundabout mid left (Old Road/Windmill Road/The Slade) follow The Slade down and the pins marked 2 Dynham Place and Girdlestone Road.
A white culvert is clearly visible at the top of the Lye under the next road south (currently the track leading from Warren Meadow to The Slade entrance of the Lye) indicating flows.
 Fig 2 and 3 will be inserted below if reproduction permission received. (requested).
This is also supported as below:
12.1 The geology revealed during the invasive ground investigation is suggestive of a continuation of the Lye Valley geomorphology with a steep narrow type gorge feature which has been infilled with alluvial type soils (clays, sands and some organic peat deposits) overlain by made ground in-fill ostensibly to raise ground levels to form a level platform (rear gardens) and later engineered infill to form a platform for Girdlestone Road. (Ref: GIS – 2DP Development)
The 1954 Town Furze Estate Plan (TFP) below shows the valley underneath the 2DP development site (yellow rectangle) – still steep ground although already some Made Ground:
An OS map from 1879 shows only one road going north (Fmr Way in Fig 1) to the immediate west of the Upper Lye, indicating the valley was too difficult to bridge – probably as it was a slow-moving stream/fen at this point.
The Slade or Slaed, means “wet valley” in Old English.
The total groundwater catchment for the Lye Valley is estimated to be 900,000 m2. The proposals set forward would see runoff from 190m2 of proposed hardstanding area change the method of surface water drainage, however it would still continue to contribute to the Lye Valley through direct discharge. This constitutes 0.02% of the total catchment area, a figure that can be considered negligible in terms of groundwater charging. (Ref: STANTEC)
WRONG – The Lye Valley catchment referred to above is not the main issue, but the catchment of the North Fen SSSI (West and East Fens) and in particular the West Fen.
The groundwater going through the site, or affected by the development, is the main concern. This is the same error, same company that advised on the Warren Meadow development.
Thames Water stormwater drains have caused severe incision, depriving the fen of water which now passes below it, effectively draining it – further additions will exacerbate this situation it is certainly not a “contribution”. An elementary error.
The relevant “Red Zone” groundwater catchment marked above is for the North Lye Fen SSSI(bright green) (comprised of the West Fen (Blue), and East Fens), as per Lamberth and updated by Dr Lamberth and Dr Judy Webb.
This is NOT the same as the Lye Valley catchment (900 ha) referred to by Stantec above, which is:
The Lye Valley, from the head to the point when it leaves the golf course, has a catchment area of 900,000 sqm. (Ref: Lamberth)
which includes the entire catchment for the Lye Valley not just that of the north unit 1 of the SSSI (North Fen SSSI) which is much smaller (The Red Zone). This is an elementary error.
From the Red Zone, the following sub-catchments, based on topological and flow data, are derived, with reference to Fig 5 above.
The West Fen catchment comprises of the Pink and Lime-Green sub-catchments (Zones) as described below.
This consists of high ground to the north, and east (rising towards Shotover), this is the part of the West Fen catchment directly affected by the development as:
The groundwater flows of the Upper Lye catchment (Pink Zone) arrive at a pinchpoint at the development site, the Lye Brook streambed, therefore will be severely impacted by the proposal.
The Pink Zone catchment’s water contribution is disproportionally high as in particular the Upper Lye Valley (Dark Purple) has very large rear gardens, old fashioned house soakaways and acts as a water conduit (see below). In addition, Rock Edge and the Wood Farm School playing fields also have the lowest proportion of built (ie lost to drains) surface area in the North Fen SSSI catchment (Red Zone).
This is also part of the West Fen catchment comprising of the Town Furze Estate and Churchill Hospital. In contrast, this is highly urbanised with high density developments with “modern” storm drainage. (as are Town Furze Estate, Peat Moors and Wood Farm in the East Fen catchment) meaning most water is lost to storm drains.
The West Fen catchment is 59.7 ha.
This proposal risks 63% of the entire West Fen catchment. (38/59.7) or 33% of the entire North SSSI catchment (38/113 ha), NOT 0.02% as claimed by Stantec which has failed to address the groundwater flowing under the site, not from it.
Stantec has failed to understand the hydrology and the riverine nature of the catchment, although explained the submissions made.
3.1.3 … Figure 1 shows the stormwater catchment areas contributing to the SSSIs as calculated by a 2007 study by OCC. This indicates that the proposed site is within the catchment area for Lye Valley Unit 1. (STANTEC)
WRONG – Hopelessly muddled – the artificially large Thames Water stormwater catchment (Orange) is shown below (Ref: MWH), the surface and groundwater catchment correspond to the Red Zone as explained above.
3.1.5 The existing rainwater falling on site is estimated to infiltrate into a perched aquifer rather than supply the main groundwater aquifer which serves the SSSI. The proposals are considered to have no significant detrimental effect on the quality of quantity of groundwater feeding the fens habitat. (Ref: STANTEC)
2.1.3 Groundwater was encountered in both boreholes rising to levels of 90.95m and 91.10m AOD. The encountered groundwater is present in the superficial deposits layer of highly compressible clay. For this reason, the groundwater encountered may be perched on the lens of less permeable clay (Ref: STANTEC)
Both statements seem incorrect, no evidence to support the “estimation” in 3.1.5 presented.
On the map below (Fig 7), Water table elevations (Light Blue, AOD and the wells (approx. 89m) are consistent and indicate clearly that there is ONE water table falling from 91.15-91.40m GIS marked 2DP at the development site), to 89.83m BGS (NE of Dev Site) to 89.65m, wells and springs at 89m (south of Dev Site), to 88.82m (WSP p.29) going from North East (NE) to South West (SW) as per Lamberth.
By arguing that the groundwater is on a perched aquifer created by superficial clay deposits of 0.9m-1.7m thickness at circa 90m is not part of the main water table Stantec seem to be stating in effect there is NO water table, as no other was found in the Beckley Sand Member to 85m which is below the level of the Lye Brook at this point! This seems patent nonsense.
STANTEC seems not understand that the West Fen is fed from ABOVE at approximately 89m depending on location, there is no water table below this.
In relation to the Warren Meadow development site WSP stated:
Groundwater elevation monitoring suggests the presence of a single groundwater table underlying the Site, with groundwater flow indicated to be in a south easterly direction towards the embankment bordering the east of the Site and the Lye Brook. Groundwater is observed to discharge on the embankment slope, forming springs. Fluctuations in groundwater level observed over the monitoring period appear to be predominantly driven by rainfall. (Ref: WSP p.5)
Groundwater levels were recorded to be shallowest (ie higher) in the north of the Site, becoming deeper towards the southeast, with flow in an east/ south easterly direction towards the Lye Brook. (Ref: WSP 3.2.1)
The detail below illustrates a consistent water table falling from North-East to South-West AND and more towards the East as it enters the valley, the development site, wells and BGS data support the view this is a NE continuation of the same water table.
Fen contributions are determined by: (After Lamberth)
- Strata incline – NW-SE
- Hydrostatic pressure and water table gradient
- Groundwater calcification – contact with limestone strata
- Low density strata to allow flows – impeded by foundations or blockages
- Ground topology, the closer to the surface, more influential
3.1.3. ….The report also states that Lye Valley area 1 (North SSSI) is contributed to by groundwater to the North East, whereas the proposed site lies due North of the Lye Valley Area 1. (Ref: STANTEC)
WRONG – Stantec seems to be very confused between the part of the Lye Valley due south of the development site (which is LNR worthy of protection), and the North SSSI to the SW. This seems unacceptably sloppy work.
The following points seem not to be understood by Stantec:
- The site is IN the Lye Valley ON the Lye streambed
- The West Fen requires groundwater from ABOVE the fen not as surface water as implied
- The development is to the NE of the North Fen SSSI which is only part of the Lye Valley, so receives its water from the area of the development site
The report is therefore SUPPORTING the position that the fen flows WILL be impacted as the site is to the NE of the North SSSI
3.1.5 … The proposals are considered to have no significant detrimental effect on the quality of quantity of groundwater feeding the fens habitat. (Ref: STANTEC)
WRONG – No data to support it and is self-referential.
3.1.3…..This indicates that the proposed site likely contributes to the Boundary Brook to the South West. The report also states that Lye Valley area 1 is contributed to by groundwater to the North East, whereas the proposed site lies due North of the Lye Valley Area 1. Contradictorily, a map drawn up later in the same report shows the site to be within the groundwater catchment for the Lye Valley (Figure 3). (Ref: STANTEC)
WRONG – There is no contradiction whatever as below.
Lamberth states flows are influenced both by topology (especially superficial flows) and strata (very gradual NW-SE):
However, on a local level the topology starts to influence the direction of groundwater movement. This means that the Boundary and Lye Brooks receive groundwater generally from a NE direction. (Ref: Lamberth p.16)
In general terms the groundwater flows within the Corallian Division follow the dip in strata from NW(E) to SW (ibid)
Fine detail of flow has been lost by this conversion to avoid over interpretation (ibid)
The diagram above, shows the flows coming from the NE, also marked by a dark blue arrow (NE), to indicate the general flow from the NE and the 2DP development site area.
Generally, land slopes southward from Old Road, and from the East to the Upper Lye Valley marked in Dark Purple.
An example flow is shown as light blue in the diagram above as numbered arrows: (1-4)
A flow comes from the NE from the Old Road area
On entering the Upper Lye Valley (unknown to Lamberth), the flow is due south down the valley possibly on the old streambed/clay layer.
The water recommences its flow from a NE direction, but from a point further south, or continues to the 2DP development site.
The water, now closer to the Lye Brook, flows SE (see WSP p.31) to emerge as seepages and springs ABOVE the West Fen or further north at Warren Meadow through Made Ground as shown
The example flow (Step 1-4 above) indicates clearly the Upper Lye could facilitate flows by enabling water to come from the north/north east, then run due south, and then resume its path from a NE direction.
Formerly, some water would have emerged as slow surface flows, some would have resumed its journey South West (ie from the NE).
Critically, a hydrostatic pressure and water table gradient MUST be maintained. The development will destroy this (see below)
Some water may emerge at Boundary Brook as claimed, far to the west (between the thin dark blue line and the Lye) but most will emerge at the first opportunity from the Lye Valley sides, as indeed it does.
The proposal will create a dam of pile foundations 18m (front) *7m (side) *10m deep transecting the Lye Valley to a depth of 10m:
The ground conditions at basement level and upper foundation level are expected to comprise made ground soils which are judged inadequate to support foundations, therefore the entire plots will have to piled in order to provide long term support..
Therefore GIS recommend that the basement and house(s) foundations is constructed via a secant contiguous or diaphragm wall end bearing within the Beckley Sand Formation at approximate depths of 10.00m. (Ref: GIS p.46 (1/1)
- Puncture the impermeable clay streambed destroying the water table, resulting in loss of water to below the level of the Lye causing loss of hydrostatic pressure and gradient required for flows to continue to the West Fen
- Stop all water flowing in the streambed
- Block flows to the wells below in the Town Furze Allotments, their only source of water (See Fig 7)
2.1.6 To avoid undermining structures, it is advised that soakaways are not located withing 5m of a slab or raft foundation of a building. Due to the tight constraints of the site, in order to implement a soakaway drainage solution, pile foundations would need to be used. (Ref: STANTEC)
WRONG – Pile foundations are required due to the site location on the 5m deep Lye valley covered with Made Ground there is NO relationship with soakaways as Pile Foundations would be required in any case, so the apparent implication one must do bad (Pile Foundations) in order to do good (soakaways) is simply incorrect.
For seepages from the Fen sides to occur, a hydrological gradient and pressure MUST be maintained across the groundwater catchment area.
Water will be entirely lost to the aquifer, relieving the hydrostatic pressure and reducing the water gradient allowing a vertical flow of water from 93m to 83m (base of Pile), well below even the Lye Brook, at approximately 86m at this location as shown above.
The proposed very heavy stone filled trench (STANTEC 3/3 p.59/p.62) will be a structure 22m*1m*1m with a base of at 92m (Purple), or 1m above the water table and streambed resting on Made Ground.
This will compress the strata and impede the ability of water to flow. It is highly unlikely it will not require further support by deep foundations as the Made Ground will not provide sufficient support.
The diverted stormwater drain will be at the same level the water table (91.4m) (eg: SW006 (91.655m) and the streambed that sustains it (doing even further damage. (STANTEC 3/3 p.62.
2.3.2 …. It is considered that these steps will help to improve the water quality in comparison to the existing condition (Ref: STANTEC)
The site currently receives rainwater, in addition and contributions from the valley sides which currently fall on tall grass which infiltrates as groundwater:
The proposed stone trench will discharge directly into the storm drain, leading to both loss of groundwater AND exacerbating the scouring of the Lye Brook streambed, resulting in water going under the fen, even if slowly discharged.
1.1.4 The site is located in flood zone 1, an area of low probability of flooding and therefore a Flood risk assessment is not required for the development which is smaller than 1 hectare.
2.3.2 The attenuation system implemented is a stone filled attenuation trench with an overflow piped connection to the surface water sewer. Water will be stored here for a period of time and released at a slow controlled rate, not exceeding the greenfield run-off for the 1 in 100 year storm. (Ref: STANTEC)
As indicated in Fig 1, locals have reported regular flooding at the site and at the former bog at 4, Dynham Place – the report has simply ignored this. (See Fig 1)
Currently this water remains in a pond on site and gradually infiltrates the ground.
The Pile Foundation dam and trench will exacerbate flooding and create a bigger pond, so the ground floor of the properties will flood regularly, as the site currently does – this is not a 1:100 year event even currently.
When water is released via the manhole orifice plates the water will enter the storm drain, scouring of the Lye Brook. In the 1970s the streambed dropped 1 metre in a short period of time.
As this is and will be a regularly flooded area, it is contrary to RE4.
3.1.2.….. For this reason it is important to consider the impact the proposed development will have on the water supply to the Lye Valley and how to best mitigate this. (Ref: STANTEC)
WRONG – The applicant must demonstrate “no adverse impact” – Mitigation is NOT sufficient, Stantec simply does not understand even what the target state is.
Surface and groundwater flow and groundwater recharge:
Planning permission will not be granted or development that would have an adverse impact on groundwater flow.The City Council will, where necessary, require effective preventative measures to be taken to ensure that the flow of groundwater will not be obstructed. (Ref: RE4)
Within the surface and groundwater catchment area for the Lye Valley SSSI development will only be permitted if it includes SuDS and where an assessment can demonstrate that there will be no adverse impact on the surface and groundwater flow to the Lye Valley SSSI. (Ref: RE4)
The onus of proof is on the developer to show this – all the evidence supports the contrary, that irreparable harm will be done by this development.
Attention is also drawn to downstream flooding in the Cowley Marsh and Iffley areas as below: (Marker is slightly inaccurate)
The development is 7 metres high with a ground level of 95m – the rear gardens of Dynham Place properties are approximately 93m, therefore the total height is effectively 9 metres, blocking light from a southerly direction.
The existing 2 Dynham Place property will be particularly severely affected.
In addition, to address privacy concerns, the façade will be inactive and blank.
Planning permission will only be granted for new development that provides reasonable privacy, daylight and sunlight for occupants of both existing and new homes. Proposals should demonstrate consideration of all of the following criteria:
a) whether the degree of overlooking to and from neighbouring properties or gardens resulting from a proposed development significantly compromises the privacy of either existing or new homes (or existing other uses where there might be a safeguarding concern, particularly schools); and
b) the orientation of windows in both existing and new development in respect of access to daylight, sunlight and solar gain (i.e. natural heating from direct sunlight); and
c) existing and proposed walls, hedges, trees and fences, in respect of protecting or creating privacy, and also in respect of their impact on overshadowing both existing and new development.
To assess access to privacy, sunlight and daylight, the 25° and 45° guidelines will be used, as illustrated in Appendix 3.6, alongside other material factors. On constrained sites with proposals for specialist accommodation, developers may use other methods to demonstrate that dwellings will receive adequate daylight.
Planning permission will not be granted for any development that has an overbearing effect on existing homes.
The alkaline fen habitat at Lye Valley is an exceptionally rare and fragile habitat. Its maintenance is critically dependent upon regular and consistent management input which prevents succession to scrub and keeps the vegetation low, as well as protection of water supply to ensure the underlying peat remains waterlogged. There has been significant input of resources to protect this site over a long period and increased management input in recent years has resulted in improved habitat condition. There remains an issue with the amount of cover of reed on the slopes of the valley in areas with the potential to support species-rich short fen of much greater conservation value. Work is on-going to address this with success in some areas but there is a need for further progress to fully meet conservation objectives. The areas of short fen continue to be of very high conservation value and support a wide range of plants which are exceptionally rare in Oxfordshire. These include Anagallis tenella, Epipactis palustris and Valeriana dioica. And although small in extent the short fen habitat is in good condition to support specialised wetland invertebrates associated with alkaline mire. The whole site is very small and isolated in the landscape and remains extremely vulnerable to damage from a variety of pressures. In particular, it will be important to ensure that management input is maintained and water supply and water quality are protected.
The site is in the groundwater protection zone both as originally defined and updated by the author. Lamberth clearly states:
MITIGATION AND ENHANCEMENT OPTIONS – SUMMARY
Groundwater protection zones are not fully mitigated by the use of SUDS therefore development within these areas must be restricted or eliminated. (Ref: Lamberth)
Headington Heritage, A personal blog
Saving Headington’s Heritage
Visit : www.headingtonheritage.org.uk
Visit : headingtonheritage.wordpress.com
Follow me on Twitter: @headingheritage
Version: 0.6 30/09/20