OFAS and HOEG meeting 4 December 2019, 13:00, at EA Osney Depot
Richard Harding (OFAS) Phil Marsh (Jacobs) Jonathan Madden (HOEG) Tim King (Ecologist) Brian Durham (SOFAG)
- Reporting arrangements for the meeting.
Each to take own notes
- Any issues arising from the OAFP meeting on 2nd October and the EA’s report.
RH unaware that the OFAS had submitted a report to OAFP saying HOEG would not meet, he would investigate and ensure that this was clarified at next OAFP meeting.
- As a representative of HOEG (JM), we wish to approach Oxfordshire County Council (OCC) Highways on flood capacity at the intended reconstruction of the A423 Southern Bypass railway overbridge. Would the EA consider any collaboration for this?
JM explained that in the New Year he would be working up his proposal for a pipeline, and it was important to be sure that it would not be `stymied' by decisions made on the design of channels under the bypass.
BD tabled OCC’s drawing of the section of the bridge. PM and RH outlined the background to the failure of the bridge bearings at E and W abutments, which had lost oil and had rusted. RH said the EA was in discussion with OCC Highways because the proposed new culverts were immediately adjacent to the existing abutments and we need to investigate the possible option to redesign. BD inquired programme on this process - RH thought asap.
RH understood there was an opportunity to replace both the intermediate piers on the existing bridge because they were too close to the railway tracks. BD had heard similar, but noted that the track in question, (up goods line) had been raised 100mm in July 2017 (GRIP3, Appendix G-1715843), and it was important to understand why the opportunity had not been taken to also adjust its horizontal alignment.
BD noted that railway headroom had been an issue in 2017, RH thought the opportunity might be taken to raise the deck to facilitate electrification. However the existing structure was old, and OCC intend to replace the whole bridge.
RH said that both existing channels were `main rivers'. BD suggested that the time to reprofile the channels beneath the A423 was when the deck was off. He therefore illustrated the principle of successive contraflows that could free up the flood arches for repair independent of rail use. PM thought that solid barriers between the columns could be used isolate the railway from construction work. RH thought that EA’s contractor would come in afterwards – BD suggested that OCH’s contractor could do it all?
BD noted that this location was a nexus of infrastructure, drainage, rail, road, HV electricity (PM added water main). He asked if anyone else present recalled seeing a network of wires forming a `cradle' under HV power lines across a motorway – could this have been to protect construction work from HV arcing? No one present was aware of this technology as an option. RH suggested this could be raised with National Grid.
TK asked about ownership of flood channels? RH confirmed the bridge structure would be owned by OCC, the railway by NR, unclear about the flood channels as dependent on who delivered them.
TK asked how NR’s recent new culverts were identified –`Dairy Crest' was suggested, PM thought they were identified simply by mileage and chainage values along the railway.
BD tabled a draft letter from HOEG to OCC’s Cllr Constance registering HOEG’s interest in the design of flood channels in the A423 bridge reconstruction. RH asked that the term `working with EA‘ be replaced by `in conversation with’.
- Likewise we wish to talk to Network Rail about revisiting the Barry Russell Option for increasing water flow capacity. (Richard Harding’s `Decision Framework‘ of 17 June 2015 (marked `official sensitive’).
BD showed a copy of the 2015 EA/NR decision framework. RH recalled the RFCC excursion that had visited the location, but thought that Barry Russell had not drawn up his proposal. Since the Russell principle had been listed as Network Rail’s Option 4 in planning negotiations, it was possible they had drawn it? BD recognised that NR’s Option 4 had provided only substructure with no mitigating flood flow, hence it had been unacceptable to EA at the time. RH referred to issues raised in BD’s email re- final destination of flood through the Dairy Crest culverts.
BD said that if a parallel HOEG letter went to NR, RH would see it in draft via the usual channel.
- BD and Roger Bettess requested Manning ‘n’ values used at selected nodes in Appendix Q on 3rd April 2019. Has there been progress in obtaining these?
BD had heard from EA Communications that OFAS would not issue Manning’s values while the present planning application was live. PM confirmed that the values themselves were not quoted in the planning application.
BD therefore sketched a section across the OFAS proposed channel. The Scheme proposed a smooth surface maintained by mowing and grazing, but if similar maintenance was applied to the existing flood plain surface (without the channel, but with local removal of hedgerows) this might justify use of the same Manning’s n values, allowing a more meaningful assessment of the effect of omitting just the channel?
TK felt that flood plain roughness was not a useful path to follow. He instead referred to a Version 13 of the No-Channel review. He was grateful for more detailed analysis including the spreadsheet. Given anomalies previously shared with RH, TK’s found that omission of the channel between Botley Road and Old Abingdon Road simplified the Scheme and eased both the planning process and the CPO inquiry, bringing improved value for money on all three counts. TK has submitted his comments to the EA and RH confirmed they will respond directly to TK on the comments in the near future.
BD asked if Version 13 was available to himself? RH said that assuming the present scheme goes for planning decision, it would be on basis of the publicly available Appendix Q (I.e. Version 5). He would be grateful therefore if BD would wait for Version 13 to be sent to him direct, rather than sharing TK’s copy.
A.O.B., and arrangements for future meetings.
BD said that his hydraulic engineer advisor had asked if EA would insist on zero head-loss at the new bypass bridge. PM said that minimising head-loss was important.
Meeting ended 14:25