barrage – Page 2 – Steve Trowbridge

05/06/201726/09/2018

Chilton Trinity and Pawlett Hams

The EA’s 2011 document Managing flood risk on the Severn Estuary provided the EA’s vision for Steart Peninsula including what subsequently became the Steart Marshes salt marsh scheme.

Pawlett Hams no longer protected after 2030

Under present plans six years after the completion of the proposed Bridgwater Tidal Barrier Pawlett Hams will cease to be defended. That means that the river banks will no longer be maintained and the process of handing more farmland back to the sea will start again. The estuary will in time return to the state it was in more than 500 years ago before the levels were drained. According to the EA this will see 387 Ha or just under 1000 acres of farmland lost to food production and the local economy although only 47Ha is actually required to make up for coastline squeeze.

The Parrett Estuary Flood Risk Management Strategy (PEFRMS) is a document remarkable for its narrow vision that is more interested in extending the habitat for birds whilst completely failing to understand or chooses to stay silent on the impact of saltwater on agricultural land. The only economic impact considered seems to be tourism.

Parrett Flood Management Recommended Strategy

Section 2.1.6 (b) notes that

North Devon and Somerset Shoreline Management Plan (Hartland Point to Anchor Head), Halcrow, due 2010. We are concurring with their emerging policies.

As such much of the real detail is provided in the EA’s Shoreline Management Plan rather than the overarching Parrett Estuary Flood Management Strategy which is a long term plan to let down the flood defences along the River Parrett allowing the sea up to the edge of Chilton Trinity and trading off land in Sedgemoor for economic development elsewhere around the Severn Estuary. It is a step back in time with individual communities afforded long term term flood protection rather than comprehensive flood defence. The high level strategy for the PEFRMS is provided below following on is information from the shoreline management plan and recently available information for the preferential flooding of farmland as part of the Bridgwater Tidal Barrier Scheme.

Pawlett Hams Realignment is the complete loss of Pawlett Hams as can be seen from the key plan in the Parrett Estuary Flood Management Strategy and noted in item c above.

Applicable Shoreline Management Plan delivery of the Strategy that includes the loss of 387 Hectares (1000 Acres of land) at Pawlett Hams is reproduced below.

Parrett Estuary (Combwich to River Brue) Policies 7d38 to 7d42

Individual policies for various sections of the River Parrett and adjacent land are listed below. 7d39 is worth noting as it has the next major realignment of the flood defences after Pawlett Hams allowing the River Parrett to come up within 1000m of the village of Chilton Trinity.

Full copies of the EA policies can be found at

Steart Peninsula (Stolford to Combwich) 7d34 to 7d37

Parrett Estuary (Combwich to River Brue) 7d38 to 7d42

Timescales

all documents refer to timescales and these are

Short Term (to 2025)
Medium Term (to 2055)
Long Term (to 2105)

Chilton Trinity

South of the Parrett the EA ultimately proposed to let the marshes return to the very edge of Bridgwater whilst Sedgemoor District Council and the EA’s Bridgwater Barrier team have left a space at site 4 for a bridge that is on the way to a planned inter tidal area and represents the expansion of the Steart Peninsula scheme up to Bridgwater.

EA presentation Severn Estuary Forum 2017

Managed Realignment

the planned retreat of the existing flood defences

Policy 7d42 Flood defences from Dunball To the River Brue

Policy 7d39 Combwich to Bridgwater (Parrett west) managed realignment.

Those two policies when implemented will along with Steart Marshes and the Bristol Ports land transform the Parrett Estuary. There will be no new link possible between West and East Somerset.

Future (long term) Inter tidal habitat – salt marsh and mud flats

Total agricultural land lost to agricultural will be around 5000 acres. There is a certain irony that the EA policies will in reducing UK agricultural land export food production abroad and potentially increase famine oversees.

In the short term the proposed secondary flood defences shown below are required because the EA will not keep raising the banks above the present levels. sea level rise will continue and the frequency of seawater flooding will increase. The route of the secondary flood defence is not dissimilar to the future managed realignment above.

Secondary Flood Banks based on Bridgwater Tidal Barrier at Site 5

The gap in the flood defences at Walpole still left open for floodwater to flood the area as it previously did in the 80’s

After the planned completion of the Bridgwater Tidal Barrier a 1:200 flood is expected by the designers to flood land to the north of Chilton Trinity with saltwater. The maps below represent some of the 50 maps prepared by the BTB designers to support the decision on location of the BTB barrier; the complete set of maps can be found on the SDC Strategic Flood Risk Assessment page.

The maps below show the impact of the river banks not being raised to match rising sea levels apart from the protected communities. The end result is the preferential flooding of farmland with saltwater during certain tide and storm conditions as presented during the Severn Estuary Forum 2017 held in Bridgwater.

None of this information was presented during the two EA/SDC public consultations in 2016.

The map below shows one of breach locations modelled. A breach can occur anywhere, the map does not say its saline (salt) flood waters escaping from the river. They are merely designed to provide an idea of the likely consequence of it happening. The full pack of maps shows a number of breach locations and these are yet to published by Sedgemoor District Council.

River Bank fails at Dunball at land to the north of Chilton Trinity flooded

One of the maps produced by the designer showing the safety risks associated with their present scheme.

BRIDGWATER TIDAL BARRIER ; SITE 5; FLOOD HAZARD 1 :1000 YEAR FLOOD EVENT

25/05/201727/08/2018

The River Parrett – how it works

Rivers that discharge into the Severn Estuary are very different from most UK rivers. With a tidal range in the estuary of around 11m MLWN -3. 0 and MLWS -5.7 AOD and the river bed level at around 0.00 AOD. These levels means that at low tide in the estuary the water level is always below the bed of the River Parrett and the river simply empties into the estuary. In the case of the Parrett its a process that goes as far upstream as Oath and the changing tide sees the river refilling from the sea.

What is seen looking over the Bridgwater’s bridges is just one half of the normal tidal cycle you would see at the coast; at low (ebb) tide its purely fresh water going out and that can be seen on the West Quay tidal gauge where the graph flattens. Equally the point at where incoming seawater (saltwater) takes over from the freshwater of the Parrett and becomes a relatively small component of the rivers water can also estimated.

At low tides the river empties so completely that during periods of low fluvial flow it can actually dry out so much so that upstream of Combwich there is an old iron age path where people simply walked across the river at low tide.

High tides can be nearly 2m above the surrounding land and at Bristol Road nearly as high as the head of the doors and over the next hundred years that will continue to grow .

Ecologically it is largely a dead river. Nature likes, however bad, a consistent environment and the Parrett offers the greatest of changes twice a day from empty to full and freshwater to saltwater. The large amounts of Seven Estuary silt that arrives with the tides exclude sunlight and there is nothing to generate oxygen. Fish(salmon) and Elvers just transit the river on their way to the fresh water of the River Parrett and its tributaries.

It is a true challenge for The EU Water Framework Directive as there is little negative actions that can be done to it. The lack of water does not deter unrealistic claims that fisheries exist in the river.

The images below show River Parrett tides ( courtesy of GaugeMap)

The Hinkley Point tide gauge above shows the full cycle of the tide in compoarison to the truncated cycle at West Quay which is caused by the river bed being higher than the sea bed in the Seven Estuary.

Looking along the river it could be shown

2014 Flood

In 2014 the Somerset Levels flooded, normally excess water is stored on the levels and then pumped back into the river when the weather improves and fluvial flows have reduced. The floods occurred because the flood storage capacity of the land was exceeded.

The response to the flood and still the current plan is pumps some more fixed ones and temporary platforms for hired pumps such as the permanent platform at Dunball made ready for the next time the levels flood and improvements made to how fast the flood water can be drained off the Levels.

One important question is whether its possible to increase the amount of water that flows down the river without pumps?

The answer is yes; the Thames Barrier is used in that way when there is flooding and the Thames and its tributaries are at capacity. The barrier gates are closed at low tide creating a shallow reservoir normally filled by the incoming tide and floodwater coming down the river fills it up. Previous references to the Thames Barrier and the River Parrett were in relation to the type of gate rather than how the system operates.

How might it work in the River Parrett?

There are two sources of fluvial floes into the Parrett. The Parrett and King SedgemoorDrain (KSD) /Sowy River. Water unable to get down the River Parrett is diverted around Bridgwater via the KSD/Sowy and re-enters the Parrett at Dunball.

Both sources can discharge when the tide is out but become tide locked when the sea re-enters the river. Creating a large temporary empty length of river downstream of Dunball would allow both sources to continue flowing and when full and matched with the tide allowed to go to the sea.

To do this a gate is needed downstream of Dunball and the best location would be Combwich or somewhere in between. The Bridgwater Tidal Barrier is a gate that could have been used to do this.

EA Downstream Scheme

The current plan is to build the Bridgwater Tidal Barrier upstream of Dunball Clyce and with sea and tide levels continuing to rise allowing the sea to reclaim the farmland at Chilton Trinity and Pawlett Hams. The existing system returning to an inter tidal saltmarsh/mudflat covering the existing farmland at Pawlett Hams and most of the land to the north of the village of Chilton Trinity. The drawing below shows how the regime will change over the years to come.

River Parrett at Chilton Trinity & Pawlett Hams showing planned next 100 years

The information can be found in

The Parrett Estuary Flood Flood Risk Management Strategy

Full copies of the EA policies can be found at

Steart Peninsula (Stolford to Combwich) 7d34 to 7d37

Parrett Estuary (Combwich to River Brue) 7d38 to 7d42

further information with flood maps can be found in the article on

Chilton Trinity and Pawlett Hams

16/05/201713/06/2017

Somerset’s 20 Year Flood Action Plan is not a Plan

Has anyone noticed there actually isn’t really a plan for managing flooding in Somerset be it Tidal or Fluvial. Lots of headlines and pictures of grandstanding councillors on river banks but little substance. Our particular collective flood Emperor has no clothes whilst the myth that somehow the Bridgwater Tidal Barrier (BTB) is part of the solution to the avoiding a repeat of the 2014 flood is allowed to persist. People imagine that things are being done and there is a big picture somewhere. There isnt.

The Somerset 20 Year Flood Action Plan is little more than a maintenance list that should have been done and wasn’t; it is a complete misnomer. In three years since the 2014 flood there is no big plan looking forward the next 200 years. There is no context that explains where the value of all the money being spent is.

There is no excuse for such short sighted behaviour by our officials and elected representatives. At least the Somerset Rivers Authority (SRA) carried out an economic impact assessment of the 2014 flood which is more than the EA and Sedgemoor District Council (SDC) have done for the Bridgwater Tidal Barrier.

The development of new ideas seems to be more akin to those seeking alternative medicinal remedies; they seem to be ones that will turn the Levels into some theme park rather than look at something that can be delivered over the decades and centuries ahead. The Managed Retreat (Realignment) of our coastline is not a panacea to rising sea levels; it has its place but needs to be challenged when there are viable options. Giving the EA the excuse and licence to do little or nothing is not acceptable. Those involved with W&WT and the RSPB as consistent beneficiaries of these EA policies and alongside Natural England makes an unholy alliance that is no friend of Somerset’s people.

Plenty of councillors are sat on committees and they should be ensuring rigorous debate and the publishing of useful information rather than the almost complete lack of detail in the public domain. The private sector would not be allowed to get away with this lack of transparency or vision.

Since 2014 when it was rushed together for political expediency little has been done or achieved whilst show case projects are not what they seem

Bridgwater Tidal Barrier

Despite knowing that the rise in sea level has no recognised end date Somerset has decided on a 100 year scheme. Our King Canute moment.

We are going to build a scheme that cannot be easily extended or modified knowing full well that something else will be needed in the future but we haven’t decided what. A scheme that unlike any conventional tidal surge barrier it is actually to be in the town rather than down stream and at the mouth of the river. Bridgwater in probably 10 rather than 100 years will have enveloped the proposed barrier site. A solution with built in obsolescence that can be bypassed on day one does not seem a great idea. Children born today may see the BTB torn down. Why would Bridgwater buy it?”

Options such as closing the gap between Stockland Bristol and Pawlett Hill less than 2 Km ( 1.3 miles) long compared to around 15 km (10 miles) both banks from Combwich to the selected site in Bridgwater or 7.5 Km if you allow Pawlett Hams to go the way of Steart Peninsula.

Two option studies paid for by the taxpayer and Combwich not even considered as an option in either and the backdoor flood route at Walpole still not acknowledged when the EA visits landowners. The credibility of the EA , its consultants and our oversight committees is very poor.

King Sedgemoor Drain Improvement

The King Sedgemoor Drain improvement is a Fluvial conveyance scheme that cannot reach its full potential because of the location of the tidal BTB upstream of Dunball Clyce. The EA in this matter described themselves in recent correspondence as the SRA’s sub contractor.

Silos

Flood schemes are kept in silos of fluvial and tidal rather than in developing a single holistic solution for Somerset. The EA and other organisations make it very difficult to see the full picture. There is a serious lack of transparency, accountability and independent review in the process.

By 2024 nearly £100m will have been spent and the Levels will still flood. The Bridgwater Tidal Barrier is seen and portrayed as a Bridgwater only scheme where as moving it downstream of the KSD outfall would increase conveyance under fluvial conditions benefiting the districts of Taunton Deane and South Somerset. The SRA is nowhere to be seen generating debate and bringing together people to achieve a wider benefit to Somerset with state and local ratepayers money which was its reason to be created. The SRA’s one big opportunity missed. This is notwithstanding the missed economic opportunity for West Somerset

Transparency

There is more information in the public domain about EDF’s Hinkley Point C power station then there is about these schemes especially the Bridgwater Tidal Barrier. It appears the EA did not want the Chilton Trinity and Pawlett Hams landowners to be aware of what would not be done to protect their land choosing to hide behind the rather opaque Parrett Estuary Flood Risk Management Strategy. Something noticeably low key to the point of invisibility in the EA’s 2016 consultations at the Bridgwater Art’s Centre.

The reasons that undertakings given by the EA and SDC in Protecting Bridgwater and the Somerset Levels & Moors from Tidal Flooding-Flood Risk Management Review -November 2014 were never followed through and just quietly dropped has never been explained.

No imagination and no vision for our children’s future

With a blank sheet of paper and little or no restrictions on what we might do to protect the South Somerset Levels including areas of Sedgemoor, Taunton Deane and South Somerset there is still a blank piece of paper. Rarely has such an opportunity been squandered.

There is nothing that explains what happens to the Tidal Surge Barrier when we cannot raise the banks any longer which in reality we cant now and Pawlett Hams and Chilton Trinity have become mudflats/ salt marsh and the cost of building downstream prohibitive.

What we do have is lots of committees

Wessex Regional Flood and Coastal Committee (RFCC)

Board of the Somerset Rivers Authority (SRA)

SRA Joint Scrutiny Panel

Somerset Drainage Board Consortium (IDB)

Its interesting to note how many people sit on more than one of these committees. These committees have people with no engineering knowledge or experience apart from the EA & IDB and all EA’s donkey work is done by US and Canadian third party consultants with no attachment to the area. The EA’s contribution to Somerset is questionable now as they have been reduced to little more than a middle man.

we must also not forget the groups

SRA Management Group
SRA Technical Group
Bristol Channel Strategic Coastal Group
South West Coastal Group
Southern Coastal Group

It really is time that Somerset had a suitable organisation capable of bringing a long term vision to secure the future of Somerset. Whilst attendance at committees is so lucrative nothing is going to get done . The EA is not a delivery based organisation and needs to be changed or replaced. The SRA has no structure or suitable people able to develop and execute the vision and solution we need. The system we have is clearly not fit for purpose.

The situation for Somerset, the rest of the West Country and no doubt other regions of the UK is that they need their own independent Engineers with local knowledge. Engineers able to provide continuity in advice to the committees and oversee the EA and IDB and other agencies.

We cannot afford

that each agency (EA, Highways, Rail) continues to builds its own thing, we need to combine flood defence with other infrastructure works.
that strategic flood decisions can be left to seconded senior local authority officers with little or no knowledge of the subject.
the lack of an independent peer review process.
The lack of transparency – there is nothing published on the BTB website that tells you why. There is little value value in an undated progress report that can be found there that does not measure progress.
all these organisations whose main purpose seems to be to invite people from other groups to attend their meetings at our expense.

WE NEED A PLAN and we need to end the Flooding Golden Goose.

on the 14th of July 2017 a meeting of the Scrutiny Committee will take place in Taunton . It is open to the public.

http://www.somersetriversauthority.org.uk/about-us/sra-scrutiny-meetings-and-papers/

03/05/201707/08/2018

Bridgwater Tidal Barrier a Fatal Flaw

The existing Bridgwater Tidal Barrier scheme has a flaw.

Water can go around it.

Any system including a flood defence system is only as good as its weakest link. The banks of the River Parrett is the Achilles heal of the EA’s scheme.

The ground along the river is simply too weak to support the continued raising of the river banks and from the EA’s point of view too expensive to maintain. The Parrett’s highest tides hidden behind the raised banks are already at the top of the doors of Bridgwater’s houses along the A38.

Even before it’s been built and the complete scheme revealed to the public the EA is working on adding secondary flood banks (dashed red lines) on the premise of a bank failure or a future decision not to maintain the existing flood defences. The drawing below is a scheme the EA has to fix the flaw. The red arrow is the open back door at Walpol where a breach to the north could circumvent all the defences. When the Dutch build a dyke they don’t build another one a few hundred metres behind it; clearly the EA expects a failure to occur or the river to over top.

The line in green is an option never considered by the EA but one that would offer much better protection than what is being proposed.

EA Secondary Flood Barrier, Downstream Bank Modifications and Alternative Barrier Route

This is information never presented to the public in any of the consultations in 2016.

To my knowledge Bridgwater will have the UK’s only tidal surge barrier not located at the mouth of the river it’s meant to control. At Bridgwater’s present rate of expansion the proposed barrier will in 100 years time not be just near the centre of Bridgwater but within the centre of its developed area. Only in Somerset would anyone come up with the plan we have and think its acceptable to have a scheme that has such an obvious flaw. Let’s also not forget that the EA’s other wider site downstream is being reserved for a road bridge to land that the EA is not protecting in the same way as existing housing. What happens when that is to be developed? Start again?

The ratepayer should have had real options presented rather than the EA’s version of the Henry Ford motto “any colour you like as long as its black”, ie anywhere in the river as long as its at the narrowest part of the river we can persuade people to accept.

The letter below confirms that the barrier can be circumvented.

EA Letter to Chilton Trinity landowner

18/04/201729/09/2019

Houses on Flood Plains

Building on flood plains is not seen as a good idea but that is only the case when you want to build the same style of house that we build everywhere and is already unsuited to our changing climate and increased recurrence of flooding. Governments have become quite irrational basis for restricting development on floodplains especially when fluvial flooding is considered in the same way as one caused by a failure of our tidal flood defences.

Somerset and similar low lying areas are not flood plains in the normal way, there is a enough room to accommodate the odd flood providing our houses are designed for that environment. There is nothing to stop development on land such as the Somerset Levels , the Fens and other low lying areas. We just need the right sort of housing.

Existing Government legislation uses a very blunt definition to restrict development but it really depends on the flood plain and what your living in which brings to the word vernacular. A misused word used by developers to continue building a product that suits their cashflow, that planners use because its safe and objectors use because apart from the great crested newt they have reasons to object and would rather put up with more of the same. We have a self fulfilling prophecy.

We cannot continue building wholly inappropriate housing just because it’s what we have become used to, our housing needs to adapt to our weather will be more extreme and flooding a regular occurrence. Flooding that in coastal areas is likely to be largely salt water rather than the largely benign floods caused by precipitation.

Its not good to have ground floors we need to put our apartments and gardens above the garages to be safe. This also means that the miserable balconies that have been provided to date need to increased to a size that is equivalent to the equally miserable gardens now considered acceptable. The difference between the two is no longer significant.

22/03/201708/08/2017

A Tidal Surge Barrier, A Bridge & Dunball Wharf

One of the problems with building the Bridgwater Tidal Barrier downstream of Dunball Wharf is the marine traffic to Dunball Wharf. Sedgemoor District Councils current draft local plan states “The Council will support the continued operation and potential development of Bridgwater Port including Dunball Wharf and Combwich Wharf (Policy D16 applies). It will also support the re-establishment of active commercial wharf’s at suitable locations elsewhere on the River Parrett. In all cases the construction or operation of new wharf’s should not adversely impact upon the Severn Estuary internationally designated site.”

The reality is that the Dunball Wharf’s with their tidal drying berths, dependency on high tides and difficult navigation is never going to be a commercial success but the 200m wide river at Combwich might. Construction of the tidal surge barrier could enable the relocation of Dunball Wharf to a better location.

Much hangs on what is considered to be adverse.

Concepts of what the river structures might look like have not been forthcoming since 2009. Apart from the tower and turning vertical gate Bridgwater’s gate structure will be considerably shorter than the Hull Barrier structure we have been repeatedly shown.

What would a barrier with a road bridge options look like?

Another wharf at Combwich, EDF have one there already, would not require an opening bridge or clearance much more than Drove Bridge on the NDR. A tidal surge barrier with a 40m fixed navigation span and a road deck might look like

Keeping Dunball Wharf would require a one larger gate and an opening bridge. Dunball currently sees 40 or so vessel movements a year so its operation would not affect the bypass traffic.

The engineering is relatively simple and with a purpose built wharf everything could be shipped in during construction.

19/03/201722/01/2018

The Great Bridgwater Gate Debate

Bridgwater’s has had a long running debate over the type of gate for the proposed tidal barrier. Bridgwater Town Council and the Inland Waterways were led to believe that only a rising sector gate, similar to the Thames Barrier, could deliver the penned solution which they want in order to maintain the water level in the river and that would be delivered. As an an attendee to the September consultation the message of a rising sector was firmly reinforced to the public when a video of a rising sector gate was continuously shown at the now selected site and various supporting images included on the static displays.

The rising sector gate aka Thames Barrier was always a red herring and never going to be built. Only a barrier downstream of Dunball where the Hanson dredgers transit to Dunball might have supported an argument for it.

Regardless of the merits of Penning the River Parrett the point made by the EA that penning could be incorporated at a later date is well made. To illustrate how that might be achieved can be seen below

Modified Barrier with Penning weir added, gates omitted for clarity.

Once the planned barrier has been built it would not be difficult to do this if it was wanted.

What is more concerning is that after 2 years of presentations people deeply involved in reviewing the scheme still do not understand it. That they feel they were led to believe a rising sector gate would be provided is completely understandable. It is also something that despite the issue being closed in November 2014 the EA have chose to keep open until now. References to The Thames Barrier, Boston and Ipswich were at best inappropriate. The Thames Barrier actually consists of a number of other vertical gate such as Barking Barrier, Dartford Barrier as well as the more famous one.

Does the gate type actually matter? No.

It is a lesson to those presenting options to the public and our representatives.

13/03/201718/09/2017

Bridgwater Tidal Barrier Location

Today the Environment Agency and Sedgemoor District Council confirmed the recommendation to build the Bridgwater Tidal Barrier within the town.

If this is built at this location everyday millions of cubic metres of saltwater will unnecessarily be brought up the river into the town and particularly North East Bridgwater. Ultimately we will get the very flood this is meant to prevent.