Riverside

Conserving Broadwater Lake

Broadwater Path opens the way to funding

Weybridge residents and visitors alike are enjoying lakeside walks along Broadwater Path, between Grenside Road and Cowey Sale. Its dedication as a public footpath and its new crushed stone surface give year round access to the lakeside – a beautful, tranquil, historic local feature, rich with wildlife.

What many don’t know is that the path is essential for the future of the lake itself. Without formal public access, the lake would not qualify for the public funding needed to stop it silting up. Broadwater is a centuries old man made lake, which requires maintenance.

Without dredging, the lake silts and becomes marshland, growing rushes then self-seeded trees. In the 14 years that residents (including PPDRA) pressed for the path, silting got worse at the Greenlands Road end. The middle length also silted badly, until residents raised funds to dredge.

Last year Elmbridge BC contributed a CIL grant, which helped fund some urgent dredging. The Broadwater Conservation Society is now seeking public funding from national sources, and wider local support.

This historic lake is an important part of local heritage. So PPDRA proposes to become affiliated to the Broadwater Conservation Society. To be voted on at our AGM on 13 September.

Broadwater Lake and Path, August 2018

Weybridge Point scheme making progress

Plans for improving Weybridge Point took a step forward on 7th December, at a meeting between the Thames Landscape Strategy (TLS), Weybridge residents groups, Weybridge Ladies ARC and local councillors.

The Weybridge Point Scheme was initiated by TLS and the Weybridge Society, and obtained CIL funding after it incorporated some adjustments to meet local needs better (proposed by PPDRA, Weybridge Ladies ARC and other local groups).

Work is soon to start. On 7th December, plans developed from previous meetings — for landscaping the car park and enhancing the ability to view the river and weir — were adjusted so that all parties were happy with the proposals.

Weybridge Point overlooks the confluence of the Thames and Wey, and is valued in many ways: as a riverside car park; as the entrance to our local stretch of the Thames Path; as part of national Cycle Route 4; as a convenient place for mooring visiting boats; and as a place with a picturesque view towards Shepperton Weir.

The Weybridge Point scheme aims to enhance its use for all of those purposes.

The draft TLS plan with a diagonal path was a significant improvement on the very first plans, but it was agreed that it needed some adjustments to avoid reducing riverside parking, to moderate cycle speed past the entrance to the WLARC boathouse, where boats are often carried across the path, and to keep the emergency vehicle access clear. PPDRA suggested some modifications.

The annotated plan on the left illustrates the agreed amendments.

Putting a dogleg in the desire line path enables maximum parking with a riverside view, slows cycles at the key point, and prevents obstruction of the path and emergency access. A low safety barrier railing will separate the parking from the riverside edge, without obstructing views.

Making the viewing platform a suitable and practical size was high on the agenda. The ground beyond the edge of the car park is fairly level before it drops away. Decking over the relatively level part would be far more affordable than decking needing a tall engineered structure for support.

There was also much discussion of how to limit litter being left outside bins. This has been an increasingly troublesome issue, since the moorings were upgraded and enlarged.

Suggestions at the meeting were for a large (commercial sized) wheeled bin with lid, for boat rubbish, plus normal bins for use by pedestrians and other visitors to the riverside. The best location for the boat bin is still under discussion, as it depends on easy access for emptying.

Overall the meeting was very positive, and all parties look forward to work starting as soon as possible, so the results can be enjoyed this summer — if at all possible, in time for the Weybridge ladies ARC Regatta on 10th June.

PPDRA has found a picture of Weybridge Point on a postcard sent from Weybridge in 1909.

It shows a view of the weir, with working horses and a small moored boat in the foreground.

Weybridge Point is a place residents and visitors alike appreciate, and true asset for our community. We look forward to it regaining some of its picturesque charm.

Broadwater Path taking shape at last

Broadwater Path – Weybridge Public Footpath 40

Broadwater Path — a picturesque walk along the edge of Broadwater lake — is at long last becoming a properly surfaced reality. The path runs through the tranquil Green Belt countryside between Grenside Road, Weybridge and Cowey Sale (Walton Bridge). Work to lay the crushed stone surface started this month, and should be completed by mid September.

At the time of writing, nearly half the length has already been surfaced, and it looks superb — a good solid surface where before there was tangled undergrowth and mud. It will be a wonderful lasting asset for our community.

Broadwater Path surfacing in progress July 2017

The surfacing is possible thanks to Community Infrastructure Levy funding secured from Elmbridge Borough Council.

The formal dedication of the public footpath by Surrey County Council was complete by the start of this year, after over 15 years of local effort to make it happen.

Broadwater Path is more than a walk though beautiful scenery — the dedication of the public footpath opens the way for public funding to help conserve the historic Broadwater lake, which has been silting up badly in recent years. We can now look forward with greater confidence to this priceless local feature being enjoyed by future generations.

The final agreed official route of Broadwater Path

RTS Walton Lane flood meeting update

Flood prevention was the main topic of an informative meeting on 19 December in Walton Lane, Weybridge, between representatives of the Environment Agency River Thames Scheme and local residents. We learned more about the status of work to model flood flows and levels, and the latest thinking on options for carrying excess water around Desborough Island.

The current preferred option is to widen Desborough Channel by cutting back the north bank (the Desborough Island side of the channel), which would avoid displacing the nationally important amenity of the Thames Path, which runs along the south bank.

The north bank is overgrown with self-seeded trees, a number of which which are reaching the end of their natural life, and in recent years several have been blown down in storms, sometimes partly obstructing the channel. (UPDATE March 2017: The picture below shows a recently blown down poplar, and scrubby trees growing into the channel.)

Widening the north bank would enable this edge of Desborough island, which has been prone to fly tipping, to be made into an appealing riverside nature amenity. It seems there is a balance to be struck in the decision however, with a few residents of Spelthorne wanting the south bank cut back.

Some Walton Lane residents meanwhile are pressing for the excess river flows to be diverted around the Spelthorne side of Desborough Island, by relocating the direction of the proposed Flood Channel 3 discharge, and dredging around the north of Desborough Island.

The current plans are to discharge the water back into the Thames by D’Oyly Carte Island, reentering the Thames more or less at right angles to the flow of the main river. Miles Macleod asked if the effects of the momentum of this 150 cubic metres per second flow entering the main stream at right angles had been taken into account (as the momentum of this flow would logically push up the water level against the south bank just before the narrow first Desborough bridge). It seems this has not yet been looked at in the 1D modelling, but the more detailed 2D flow and level modelling will seek to incorporate it.

Headlines from the meeting:

Bottom line of the RTS is that it should cause no increase in risk anywhere
At the top of Desborough current modelling shows a 0.04 to 0.11 metre reduction in flood levels
Modelling has been calibrated using data from six real flood events
Calibration of the model includes past flows from all sources (fluvial and groundwater)
Target accuracy is +/- 0.15 metres (i.e. it might not actually reduce levels at Desborough…)
The river bed beneath the Desborough bridges will be lowered by around 2 metres to accommodate extra flow
Current preferred option for increasing flow around Desborough is to cut back the north bank of the Cut

We had a number of questions for which immediate answers were not available, and the EA team have very helpfully now supplied these. Some key points are that:

The total volume of water occupying the floodplain in a 1 in 20 year flood is equivalent to about six hours flow of the Thames
Extra total flow downstream of the RTS relief channels caused by that water draining from the floodplain is modelled at about 5-10 cubic metres per second (cumecs) in a total river flow of 500 cumecs
More water currently flows around the north of Desborough Island around the old river loop than flows down Desborough Cut; this position will be reversed by the changes proposed in the RTS
The width of the channel under the first Desborough bridge below water level is 23.2 metres (and this will not be increased); the modelling takes this into account

Once again, we are extremely grateful to the River Thames Scheme team for the time and effort they are putting into keeping our local community consulted and informed.

UPDATE: North bank of the Desborough Cut, viewed from the Thames Path on the south bank in February 2017. Note the poplar blown over in a recent storm, and various trees growing out into the channel obstructing flow.

Thames Lock – new gates and tour

Thames Lock in the Wey Navigation has a new pair of lock gates, and residents were give a rare opportunity to inspect them from inside the lock at the end of November, on completion of the work. Large numbers of interested visitors were treated to tours by guides with a deep knowledge of the Wey Navigation history, construction and maintenance.

The wooden lock gates last about twenty years, and this year it was the turn of the lower gates to be renewed. Temporary barriers were installed immediately upstream and downstream of the lock, and the water pumped out. The huge gates are held in their hinges by gravity, so changing the gates was a matter of hoisting out the old and lowering the new custom-built gates into place.

This empty lock gave a rare chance to view the parts of Thames Lock that are normally under water. The upper gates are smaller, as they sit on top of the step to the higher level of the navigation.

The floor of the lock was originally wood — which is preserved by being under water with very little access to oxygen — but was replaced by concrete some time ago. The step beneath the upper gates is still made of wood, and includes original Elm baulks which have survived hundreds of years since the navigation was constructed.

Lock gates suffer decay because they are exposed to air and water. The effects can be seen in the old lower gates, pictured here waiting to be taken away by barge. One can only wonder how many boats have those gates have helped pass up and down the Wey Navigation.

TLC needed for Weybridge Thames riverside

Wouldn’t it be lovely to have a riverside we can be proud of? Many Weybridge residents recall how attractive our local stretch of Thames riverside was, up until autumn 2009 (see our main picture). A well-tended riverbank where people could sit on the grass in the sunshine or in the shade of a tree, and enjoy fine views and tranquility.

Then the Environment Agency cut down the trees and fenced off this prime stretch, between Weybridge Ladies ARC and the foot ferry, in the course of works to install concrete moorings. They left the temporary fence in place and the riverbank untended for five years, despite local protests. It looked like this in 2014.

PPDRA along with local residents pressed for access to the riverbank to be restored and the brambles removed…

…and the mesh fence was eventually removed, and the brambles that had grown up behind it were strimmed.

But the riverbank has subsequently been left untended, and has again become an unattractive bramble patch. Below is a photo of the same stretch of riverside as in our main picture, showing how it looks in September 2016: overgrown, with brambles and scrubby growth obstructing access and views.

This is the first length of riverside seen by people joining the Thames Path at Weybridge. It is a significant local amenity. Surely it deserves some TLC?

We want to see this important piece of riverside getting the care it deserves, with a proper mowing regime to maintain it as a grassy riverbank people can enjoy. Together with the Weybridge Society, we are lobbying councillors to bring back regular mowing of the grass along this prime stretch of riverbank, to give residents something they can be proud of once more.

LINKS:

Read about the history of the riverbank work here

Read about the ‘Thames Gate-Wey’ moorings scheme here

Walton Lane Weybridge flood update meeting 1 Aug 2016

The latest River Thames Scheme (RTS) developments and local flood prevention measures – including a possible temporary local flood barrier – were top of the agenda when Walton Lane residents (plus PPDRA Chair Miles Macleod) met with representatives of the Environment Agency and the RTS modelling team on 1 August 2016.

Costs and Benefits of the RTS

We were told that the projected costs of the River Thames Scheme at current values have risen to £476 million, and of that around £250 million has been promised so far (£212m from the Government, £36m from partners). The scheme would have significant benefits in terms of flood relief for residents between Datchet and Shepperton.

The RTS aim for residents of Weybridge — where the proposed Flood Relief Channel 3 would discharge — is that the scheme must not cause any projected increase in local river levels.

In parallel, the Environment Agency (EA) is looking actively at what can be done to mitigate local flood risk in Weybridge.

RTS flows and levels – 1D modelling

While the RTS 2D model (which should give more accurate modelling) is still undergoing peer review, we saw some highly relevant outputs of the latest 1D modelling of local flows and levels in different states of flood, modelled without the proposed Flood Relief Channel 3 in place. The modelling projected local flood levels on land around Walton Lane which very largely coincided with past local experience of actual flood levels. This reflects well on the quality of the modelling work.

Once the 2D model is available, probably by the end of September, it will be run to simulate flows and levels with Flood Relief Channel 3 in place. Then we will be able to get a better indication of the anticipated local impact of that proposed new channel (with its 150 cubic metres per second capacity) discharging at Weybridge

Models of Desborough alternatives

Meanwhile, on 1 August, we were shown the latest 1D modelling of alternative possibilities for works on Desborough Cut or around Desborough Island.

Five possibilities were presented, each of which has now been 1D modelled:

Widening Desborough Cut by 3 metres on the south bank
Widening Desborough Cut by 3 metres on the north bank
Dredging Desborough Cut
Dredging downstream of Desborough Cut
Creating ‘Doug’s Channel’ across Point Meadow and dredging north of Desborough Island

All five possibilities would succeed in avoiding an increase in river levels locally at Weybridge, according to the latest 1D modelling. Choices will be made later — we are told this will be after 2D modelling and after further consultation — using a range of criteria, and not simply on up front cost.

Option 5 would cost considerably more than others, as it would involve a huge amount of excavating and dredging. The 1D modelling suggests it would require, as well as cutting a channel across Point Meadow, the dredging of 35000 cubic metres of riverbed (20m wide and 2.2km long) to prevent the upstream RTS works increasing flood risk locally. This option would have a neutral effect north and east of Desborough Island, and would bring the benefit of decreased flood risk at Weybridge.

Impact of silting up again after dredging or widening

1D modelling predicts that the dredging options (3 & 4) would require 12,000 cubic metres of dredging along 1.1km of Desborough Cut, or 10,000 cubic metres of dredging along 1.0km downstream of Desborough Cut, to have a neutral effect at Weybridge.

In discussion it was suggested to us that – while no decisions on preferred option are being made at present – dredging would have major maintenance implications, which are likely to make dredging Desborough Cut less desirable than widening.

We were told that the River Thames in normal flow ranges achieves a self-managing equilibrium, with silting and scouring occurring as flows change. Hence if dredged it would tend to silt up again (because dredging would allow normal flows to be carried at a slower water speeds) and it would tend to revert to its natural depth profile needed to carry its normal flows, unless regularly dredged.

One question which we did not think to ask at the time, was ‘would the same not be true of widening the Desborough Cut?’. Widening the Desborough Cut would allow normal flows to be carried at a slower water speeds, so would not a widened Desborough Cut similarly tend to silt up and become shallower, hence reducing the maximum flood flow capacity, unless it was regularly dredged back to its current depth? We are following up on this question.

Implications of widening Desborough Channel

In comparing options 1 & 2, widening Desborough Cut one side or the other, participants were agreed that there are more things to consider than simply cost and increased flow. A very significant factor is loss of amenity – something which led Elmbridge Borough Council to conclude in 2010 that it could not support the proposals for cutting back the south bank.

If 3 metres of the south bank were to be removed along the length of the Desborough Cut, this would have a serious impact on the amenity and appearance of this stretch of the Thames Path and National Cycle Route 4. It would mean moving the path in places closer to the traffic of Walton Lane, and would forever change a popular riverside path which is used by countless people. There would also be a potentially costly logistical question of how to manage works which would require a national path and cycle route to be closed during those works.

We learnt that the profile of the river bed of the Desborough Channel is not, as previously suggested, vertically deep on the piled south bank and shelving on the north. In fact, close to the south bank it has a shelving river bed, and the piling is simply there to hold back erosion. Hence cutting back the north bank would not necessarily be significantly more difficult or different in terms of flow impact.

Widening on the north bank would also enable the Environment Agency to deal with those elderly self-seeded trees on its riverside land along the north bank which are in an increasingly poor state, with branches breaking off and trees falling into the river with each major storm.

Bridge bottlenecks in Desborough Channel

A serious concern for Walton Lane residents is the bottleneck in river flow caused by the first bridge across the Desborough Cut. The bridge is much narrower than the channel either side, and it would be too costly to widen it if widening Desborough Cut.

At present, water backs up in times of high flow, with visibly different levels either side of the bridge – high enough on the upstream side that it flooded a neighbouring property in 2014. The river bed was scoured deeper beneath the bridge by those extreme flows of the 2014 floods.

This bridge would become an even more worrying bottleneck if Flood Relief Channel 3 is constructed, increased the potential maximum flow arriving at the bridge.

To facilitate flow under the bridge, the EA is proposing to dredge beneath the bridge, to create a permanently deeper section of river which will be easily scoured in future high flows; also to modify the profile of concrete banking upstream of the bridge.

As a short term measure, residents have funded a small earth bank to help hold back floodwater from overflowing the bank at this point, but more could be done, and more needs to be done if the RTS proceeds with the construction of Flood Relief Channel 3.

EA Proposals for Temporary Flood Barriers

The 1 August Walton Lane meeting was also told of proposals for local flood prevention measures, aimed to protect residents of Walton Lane and Dorney Grove.

These plans are still work in progress by the Environment Agency, but they including a possible temporary local flood barrier which could be erected at short notice to prevent flood water from the River Thames reaching Weybridge homes.

The temporary barrier could run from the bottom of Thames Street and along the Thames Path towards the first bridge across Desborough Channel.

The initial draft route for the temporary barrier would have blocked Walton Lane, and excluded some houses from protection, but residents at the meeting suggested extending the barrier slightly to the point where Walton Lane rises above flood level, avoiding the need to put a barrier across Walton Lane. On the other side of Walton Lane a length of barrier would help prevent water from the engine river reaching homes.

The EA has purchased 40 km nationally of this modular temporary flood barrier system, and Walton Lane / Dorney Grove is a target area for protection. The EA draft plans for Walton Lane are being amended following our meeting, to reflect the suggested rerouting. Further work will be done to look at the relative risk from river overflow and from rising groundwater (which the barrier could not prevent).

Potential for a permanent flood barrier?

Our meeting also discussed the possibility for a more permanent barrier along the river edge between Thames Street and the first Desborough Bridge, either in the form of a bank alongside the path or slightly raised path (as per the Wey Navigation).

Important factors beyond its effectiveness at holding back floods would include the aesthetics of flood protection works along this stretch of the Thames Path, impact on amenity, and the practicalities of easy river access for the WLA Rowing Club, Weybridge Sailing Club and the Canoe Club

Future River Thames Scheme consultation

RTS workshops are planned for the end of September, and Walton Lane Residents anticipate a further update meeting once the 2D modelling has been conducted of river flows and levels at different flood probabilities with Flood Relief Channel 3 in place.

Broadwater Path one step away

SCHOOL DECISION DELAY

Fourteen years of effort by local residents and councillors have gone into getting agreement and funding for the Broadwater Path, along the edge of Broadwater Lake. As well as being a magnificent facility for the community, the path will help ensure the future of the lake itself. But there is an unexpected last minute obstacle.

Just as Surrey County Council was poised to complete formal dedication of Footpath 40 (Broadwater Path) in April 2016 and to begin work on laying the surface (with CIL funding agreed by Elmbridge BC), local residents were dismayed to learn that St George’s Weybridge had decided to oppose dedication of the path across its newly acquired land, despite a previous Deed of Planning Obligation.

So everything is on hold, except the continuing decline of the lake.

Broadwater Lake is progressively silting up and desperately in need of substantial dredging works and maintenance. Formalising public access to the lakeside will do more than simply give walkers a better path: it will open the way to public funding for maintaining this historically significant lake and exceptional local natural environment.

Strong local opinion

Local community groups have lobbied the school, seeking a change of mind. On 21 April 2016, PPDRA Chair Miles Macleod, presented a comprehensive case for permitting the dedication – you can download a copy of the PPDRA Broadwater Path Submission to School Governors here. You can also download the maps and plans. As you can read in the submission, the path may possibly be formalised with or without the school’s agreement, but school consent would greatly reduce the unexpected delay.

Subsequently the school has informally suggested a possibility of permitting a re-routed path. This would involve a diversion away from the lakeside before the school land, and along the paved lane from the health club.

In sounding this out, we have heard some strongly expressed views that the school should permit the original lakeside route. At our May PPDRA Committee meeting, after extended consideration of matter and of the school’s alternative route proposal, the view of the committee was strongly in favour of continuing to press for dedication of Broadwater Path along its original proposed route. We also agreed to continue seeking further views from the local community.

The path alongside Broadwater has been used informally and unopposed for as long as anyone can remember. Formalisation of the path alongside Broadwater Lake would bring benefits for the school as well as the community.

What are your views? Please do take a look at the facts set out in our submission.

Note: The picture on this page shows the new land purchased by the school in red, the Broadwater Path (proposed Footpath 40) in green, and Footpath 36 (which separates the old and new school land) in yellow.

Walton Lane Environment Agency flood meeting

Residents of Walton Lane, Weybridge, have gained new insights into the Thames Scheme flood plans by talking directly with people working for the Environment Agency on modelling river flows and levels.

A very informative meeting in Walton Lane on 25 April was attended by local residents, including PPDRA committee members Doug Myers and Miles Macleod. In the course of the meeting it was agreed that flows of specific alternatives to widening Desborough Cut would also be modelled.

Headline learnings from the meeting include:

The 2014 floods were a ‘1 in 15 year’ event, based on historic evidence
Flooding has been unusually light in the Thames Valley for the past 40 years, so public expectations of flood risk are low compared with historic reality (and possible extreme events from climate change add more risk)
Flood Relief Channel 3 which discharges at Weybridge would carry its full design flow of 150 cumecs (cubic metres per second) at much lower total river flow volumes than reached in 2014 (which was 500 cumecs)
The flood relief channels would INCREASE the projected risk of Weybridge flooding unless something is done to increase flow downstream of Weybridge
The criterion of acceptability is that the works must NOT increase the predicted river levels for projected flood flows at any point (so downstream works are essential)
Widening the Desborough Cut on its south bank is the cheapest option to increase flow downstream (requiring driving in new vertical sheet piling to define the new bank and excavation of the current bank)
Widening on the northern bank of the Desborough Cut would be more expensive, as it has developed into a more natural kind of shelving bank with many trees limiting flow
Cost is a critical factor
Modelling predicts that Desborough Cut does not need to be widened much along its lower half: widening the upper half and dredging at the first bridge would increase flow sufficiently
Widening the bridges would be expensive (and has not been budgeted for)
The 2014 floods scoured the river bed at the first Desborough bridge, significantly increasing the depth at that point
The Environment Agency are looking into potential alternatives to widening Desborough Channel (but the indications were not particularly positive)
Cutting ‘Doug’s Channel’ through Point Meadow (the north-west horn of Desborough Island) would also require widening or dredging of the remainder of the northern old river loop, which would be costly
The modelling team agreed to model the effect of this northern alternative approach on local levels and flows

Modelling of levels and flows is a highly complicated process, and not a precise science

1D modelling is relatively quick, but only considers the flow within the confines of the river
2D modelling includes flow in the adjacent flood plain, when levels are high, but is slow and very complex
Peer reviewing is a hands-on process, involving CH2M (formerly Halcrow) peer reviewing the JDA model and the design works, in “a process of questions and answers that get to an agreed design”
The overall margin of error in modelling appears to be higher than some of the predicted local changes in level which modelling suggests the scheme will produce, though the calculation of possible modelling error is far from straightforward
(Editor Comment: A truly robust approach would demand that the projected effects must be greater than the margin of error. However, logically the estimated margin of error of modelling can only be based on experience of disparity between modelled flows and actual measured flows.)

Future action timescale

Currently the River Thames Scheme has Treasury approval for the outline case (as previously reported)
Modelling with the latest data is in progress, 1D now, 2D in the coming months
A definitive outline design is planned by the end of 2016, following workshops
Scheme detailed design will follow that
Works timetable is for weirs work in 2018, relief channels in 2020

LATEST NEWS: UPDATE FROM ENVIRONMENT AGENCY 26 MAY 2016 SHOWS FUNDING SHORTFALL

OPINION: Thames Flood Diversion – Time For A Rethink?

The River Thames Scheme: piecemeal planning based on unreliable evidence?

OPINION by Miles Macleod
– The following article expresses the views of the author, and does not necessarily reflect the views of PPDRA.

Will the plans for River Thames flood diversion channels be an effective solution for flooding, or a source of bigger future problems downstream and increased flood risk to London?

The Environment Agency’s River Thames Scheme proposes three new flood relief channels alongside the Thames, intended to reduce flooding between Datchet and Chertsey. The final channel, with a capacity of 150 cubic metres per second, would be cut past Shepperton and discharge at Weybridge, opposite the Canoe Club.

‘The River Thames Scheme’ is perhaps a misleading name. Originally called The Lower Thames Flood Risk Management Strategy, it covers the stretch of non-tidal river between Datchet and Teddington. Not the whole River Thames.

Capacity increase funded, impact unknown
Downstream of the three planned relief channels, the River Thames Scheme proposes to widen the Desborough Cut at Weybridge, and to increase flow capacity at Hampton, Molesey and Teddington Locks, to carry extra water onwards towards London.

What would the effects be at Weybridge, and downstream towards London? Would it increase the flood risk?

At present, the Environment Agency can’t say. Why so? Because “the hydraulic model that will be used to assess the impact of the RTS (including downstream of Teddington) is currently being finalised“.

Yet over £300 million funding for the River Thames Scheme has been promised, on the basis of old assumptions and outdated flood risk and flow predictions. Meanwhile – as we will see later in this article – senior figures in the Environment Agency itself are questioning existing thinking on flood protection.

Risk to London
In the 2014 floods, the existing River Thames flow capacity carried 500 cubic metres per second of water over Teddington Weir. The Thames Barrier had to be deployed repeatedly, in sync with normal tidal flows, to help carry the excessive river flow onwards, and hence prevent flooding in the tidal Thames.

The River Thames Scheme proposes to increase the potential flow arriving at Teddington Lock by another 150 cubic metres per second. Will that increase in flow capacity lead to an increase in the flood risk to London? At present, the Environment Agency can’t say.

Some of us are deeply concerned at what seems like a succession of uncoordinated plans – different project schemes, with different political sponsors, looking at different parts of the river – moving the flood risk progressively downstream.

Previous experience
In 2002, a flood diversion channel bypassing Maidenhead, Windsor and Eton was opened. It discharges just upstream of Datchet. Called the Jubilee River, and costing £110 million, with a capacity of around 170 cubic metres per second, it has helped divert floods from Maidenhead, Windsor, Eton and Cookham.

In the years since the Jubilee River was opened, flooding has increased from Datchet downstream. That, according to the Environment Agency, is a coincidence. They say that the Jubilee River “operates so that flood levels downstream are not adversely affected”.

Local concerns
In 2009 the Environment Agency put forward the Lower Thames Flood Risk Management Strategy, setting out plans to address the flood risk downstream of the Jubilee River. That raised hopes for some people, and worried others.

In Elmbridge, people were concerned by the potential downstream effects of a flood relief channel discharging at Weybridge, and also the proposals for cutting into a significant amenity, the popular stretch of the Thames Path and National Cycle Route which runs alongside the Desborough Cut. The Environment Agency called this an ‘access track’. They proposed to widen this side of the Desborough Cut by 3-4 metres, and move the ‘access track’ closer to the road (Walton Lane) – but not to widen the two bridges across the Cut, which are existing bottlenecks restricting flow.

Elmbridge objections
The author of this article, Miles Macleod, was at that time an Elmbridge Borough Councillor for Weybridge North. That is where the planned third flood relief channel would discharge, bringing 150 cubic metres a second of additional water flow capacity. He alerted Elmbridge Borough Council to the implications for the Borough of the plans. Others councillors agreed that this was a serious issue for the Borough.

Elmbridge Borough Council studied the plans, and was concerned. It concluded in January 2010 that it could not support the plans for widening the Desborough Cut – plans which would need the Council’s consent.

Elmbridge Borough Council also said that the projections for flood risk and flows needed credible independent external verification, and fluvial and tidal flood strategies should be coordinated.

PR campaign
The Environment Agency found that in the financial climate of the time it could not secure funding for its Lower Thames Flood Risk Management Strategy plans. So it spent five years actively promoting the plans and the projected benefits, using its old flow calculations as evidence. It renamed the strategy as The River Thames Scheme – a name suggesting something more far-reaching than the lower Thames between Datchet and Teddington – but still could not raise enough funding.

Then the February 2014 floods came upon us, with particularly severe effects on residential areas between Datchet and Chertsey (downstream of the Jubilee River). The result was political pressure to fund the proposed Lower Thames flood relief channels between Datchet and Weybridge (and the wider Desborough Cut). At the time, a general election was not far away.

Lo, the remaining funding for the River Thames Scheme was secured. And it was secured despite new evidence about river flows and flood levels – experienced in the 2014 floods and more recently – which raised serious questions about existing flood risk and flow calculations and modelling, including those underpinning the River Thames Scheme.

Misguided approach
The relief channels should help moderate short term extreme peaks of flow, but if there are extended periods of very high flow they have the potential to increase the total volume of water flow arriving at Weybridge by some 30%.

The Environment Agency reassuringly says that the differences in projected flood risks are expected to be small in the revised calculations, drawing on recent evidence added to the accumulated evidence of the past 130 years. But the fact remains that the scheme begs questions which at present don’t have good answers.

The answers may continue to change: with a changing climate and more extreme events, we cannot rely so much on probabilities calculated from the frequency of past flood events. Flood risk models must build in higher probabilities of known maximum flows and levels being exceeded.

Complete rethink
There is a basic concern.

Flood defences need a complete rethink. Who says so? The Environment Agency.

Rarely has a truer word been spoken.

The Agency’s deputy chief executive, David Rooke, has said the UK’s climate is entering an era of unknown extremes, and that a complete rethink of flood protection and resilience across the country is needed.

The £300 million River Thames Scheme plans are based on calculations of risks and flows which recent evidence has already shown to be unreliable. They reflect a limited view of flood protection, and potentially increase flood risk to London from an extreme event, by significantly increasing flow capacity into the tidal Thames.

New approach needed
Successive extreme floods in various parts of Britain have led many people to the conclusion that current flood strategies are flawed, too narrowly focused and trying to tackle flood problems in the wrong way.

Piecemeal plans which move flood risk downstream are unacceptable.

A new approach is essential. The Thames needs a better thought out whole catchment plan, to help reduce the size of flood peaks along the length of the river – even in extended periods of exceptional rainfall.

A whole catchment plan might start with initiatives to slow down inflows along the length of the river, rather than trying to increase capacity in first one problematic stretch of the river, then another downstream.

Yet the River Thames Scheme appears to be going forward with great determination, to deliver what history may judge to be a very expensive mistake: an outdated, narrow and ultimately damaging project.

Time for that complete rethink? It is not too late!

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