Bridgwater Tidal Barrier Final Public Consultation

Ahead of the forthcoming last public consultation on the Bridgwater Tidal Barrier (BTB) the rate and tax payers might consider asking what becomes of Bridgwater after the BTB reaches the end of its design life?

The answer is simple.  

if there  is no barrier capable of keeping the rising sea out there will be no house insurance, no mortgages and Bridgwater the town will not be a viable place to live. 

Our present proposed EA flood defence scheme is based on retreating as far back from the sea as we can, it deliberately  puts our backs to the wall  On one side of the barrier we will ultimately have the inter tidal habitat (the sea)  and on the other our housing and industry.

No space is being provided behind the proposed barrier to create another bigger one. As a consequence there will be nowhere to go with a replacement that does not have a huge and unnecessary price tag. There is an irony that land at Chilton Trinity returned to the sea under the present scheme  and the planned managed realignment in 2055  will be inadvertently reclaimed  under a downstream replacement barrier albeit land now poisoned with salt.

With sea level rise continuing for hundreds of years past the design life of the BTB one would expect that as responsible people we would give some consideration to what happens next. Unfortunately, like so many things in need of fixing and investment we seem content to kick the problem into future refusing even to consider how we might make some provision to help those that follow us.

Many years an Arup engineer called Poul Beckmann wrote  the opening sentence of a  document with the line “Human nature is that we put off until tomorrow what we should do today”. Never has that been more true today than in Somerset. Somerset’s failure to develop a realistic, affordable and sustainable long-term strategy is unforgivable.  It really is time for some of the promises made by our political leadership on this issue to be delivered and people stop making excuses why things cannot be done. Simply working our way through the Somerset 20 years plan and saying the future is not our business is irresponsible and unacceptable.

what was the question?

The SRA was asked “What is the SRA and its partners working assumption for the replacement of the existing scheme and barrier?

The written answer received from the SRA  answer is in blue

From day one, the tidal barrier will be designed in such a way that it will still provide a 1 in 1,000-year standard of protection in 2125. The design includes an allowance for climate change up to 2125.

  • Climate change does not stop in 2125!!!! 
  • 1:1,000 sounds good but its just the margin on the starting point and degrades over time. The Dutch use 1;10,000 and maintain it as the level of protection.

The downstream defences will be designed in such a way that they will still provide a 1 in 200-year standard of protection in 2055, with allowance for further adaption for climate change over time.

  • 2055 is important because this is the date from which managed realignment is implemented under Policy 7d39  of the Shoreline Management Plan.
EA explaining the scheme in 2017

It is to be expected that any piece of infrastructure would need updating after 100 years. We cannot decide now how future generations may wish to live or what their priorities for infrastructure will need to be. This is why, for example, there are plans for the Thames Barrier to be re-built in future decades but decisions on exactly where and what will be required are deliberately being left for later.

  • Building the barrier in the town as planned does not  give those in the future choices but leaves them no choice to but to go downstream and  use land we have previously given back to the sea and to abandon the £100M investment the present scheme will have cost.
  • The response attempts to conflate the need to replace the  1970’s Thames Barrier as a reason not to make provision today for a replacement  in Somerset. if you know you have to replace something why would you not plan for the replacement? Its an excuse. 
  • We should be learning the lessons of the past rather than making a  virtue of repeating the failures that the SRA reply implies.

The Thames Barrier Myth

The continual portrayal Thames Barrier shown on TV as an iconic single barrier solution is misleading; the barrier is actually part of the Thames Estuary flood defence system comprising not one but eight individual tidal barriers that all shut together. Five of the eight barriers are closer to Bridgwater’s  situation than the “Thames Barrier”. They are however where they should be at the mouth of the rivers they defend not 5 miles upstream as with Bridgwater’s Tidal Barrier.

Thames Estuary Flood Defence

Using the Thames Barrier as an excuse for not planning a replacement in Somerset is particularly disingenuous  for a number of reasons.

  1. Nearly 60 years ago  when the Thames Barrier was designed climate change was not understood as it is now. There was little provision for sea level rise just the post Ice Age tilt of the south of England to consider.
  2. The  Thames Barrier is upstream of what were active docks  that had navigation rights in the Thames Estuary.
  3. In Somerset we have a topography in the form of the Polden Hills, Pawlett Hill and Stockland Bristol that we can link and use to our advantage.  London does not have such a luxury.
  4. All the Thames Barrier replacement options  move the replacement barrier  downstream perhaps as far as Tilbury. (July 2016 update)
  5. The  most frequent use of the Thames Barrier is now the management of fluvial flood water rather than tidal surge. Something Bridgwater is not designed to do.
  6. Sedgemoor District Council is able to reserve space for a bridge over the Parrett south of Dunball should its not be doing the same for a replacement barrier?

The collective response is No ; there is no plan.

The SRA, EA and SDC were conformed as having contributed to the response

Bridgwater Tidal Barrier; the Questions the public need to Ask

Once  the question “how will the proposed Bridgwater Tidal Barrier be replaced?” the present  scheme simply looks out of date and poor value for money.

The Bridgwater Tidal Barrier is repeating the same mistake as was made with the Thames Barrier system setting it as far upstream as possible. Because of the selected location  a replacement would like the Thames Barrier have to go downstream towards Combwich. Confused? We should be.

When you go to public consultation some questions worth asking;

  1. How will the proposed Bridgwater Tidal Barrier be replaced?”
  2. What becomes of Bridgwater after sea level rise exceeds the design basis of the Bridgwater Tidal Barrier?
  3. Why is there no long-term plan or vision for what comes next?
  4. Why is the ratepayer required to provide money to raise river banks money protecting land at Chilton Trinity when the planned sea water flooding will make it of no economic value?
  5. Why is not improving fluvial flow in the river system  part of the scheme?
  6. Why did the cost of the scheme almost double after the location was decided on?

Sustainable Flood Defence

The UK has a serious problem with leadership and sustainable construction where flood defence is concerned. There is a profound lack of critical thinking in the delivery of future UK flood defences and an unwillingness by agencies to get their  hands dirty at a local level. As a consequence government continues to fail regarding sustainability and value for money; taxpayer funded agencies seem unable or unwilling to work together.  It is a situation compounded by wildlife and environmental organisations who have seen an opportunity to gain control of and modify land in much the same way that monasteries such as Glastonbury once did.

Flood defence schemes are invariably seen in terms of a definable project that can be closed rather than the first step of a sustainable long term solution. The protected community needs to live with and manage these schemes  for 100’s of years after they are built. Our thinking on delivery is just too short and too expensive when it is a 300 year or so problem and especially when the initial solution only has a 100 year design life; it makes little sense. There is an obvious gap. That gap  means that today’s options should at least consider what happens next. Should we really  be adopting a solution today requiring the construction of a  replacement barrier tomorrow rather than a scheme today that has  provision or a plan for extending it already built in? Our current scheme takes planned obsolescence to a new level.

We should not be closing out future options for the generations that follow and we should follow our own rules for sustainable development

“Sustainable development is development that meets the needs of the present, without compromising the ability of future generations to meet their own needs.”

Delivery of the Bridgwater Tidal Barrier continues to be an exemplar of non-sustainable thinking. Part of the scheme requires the river banks between the tidal barrier and the village of Combwich to be maintained. The EA’s plan to do this work as part of the barrier construction contract. Material is to be dug from the adjacent protected fields  and where a future Northern Bridgwater Bypass might be routed.  Sedgemoor District Council (SDC) have protected in the Local Plan a potential crossing point on the River Parrett just south of the  A38 roundabout at Dunball.

Clearly excavating Chilton Trinity’s fields and creating a series of salt water pits that creates an ideal future breeding ground for salt marsh breeding mosquito’s is not what people have considered the consequence to be. It is far from impossible that in a generation Chilton Trinity and Combwich may ultimately become uninhabitable because of this excavation process rather than from the increased flood risk. Managing mosquito borne diseases may well become the larger challenge in low lying areas as our climate warms up. It is difficult to see how the EA could contemplate the creation of such a situation.

With whole life costs of the Bridgwater Tidal Barrier reaching £100M for a barrier, secondary banks and the raised river banks; banks that need continual raising means we need to consider modification of the delivery model to get the costs of this project under control.

That whole life cost  also ignores the 100 year economic impact,  both locally and nationally, of losing 1000’s  of acres of productive agricultural land  notwithstanding the questionable morality of a food importing country  choosing to export more of its food production offshore. 

If we are going to build the solution we have we need better and more economic delivery solutions than is currently proposed. We can then at least  ameliorate the present situation with a better delivery system.

Brexit allows the modification of the EU water and waste directives  that have now been written into UK law. We can now change the way in which we manage waste for the better.

Sustainable Construction

Every year Sedgemoor will build 5-600 houses and the excavation of foundations and drains for each of these houses will create around 15-20m3 of waste material (clay) suitable for re use as bank raising fill material. Sedgemoor’s  planned housing developments  will create around 9,000m3 per year that currently must be paid for to be disposed of. Housing developers could supply all the material needed to raise the banks. That is sustainable construction.

Over the 100 years life of the barrier there could be as much as 900,000 m3 of material we need to find a home for; material that could be used to build up the banks and preserve the land we have at Chilton Trinity for future generations. Even if the volume is  only 10% of the possible amount its probably enough to avoid digging up land at Chilton Trinity.

Under present EA proposals the EA is going to pay landowners for material that other organisations with similar material must pay to dispose of. We are meant to be reducing this sort of activity not making the situation worse.

We simply don’t need to get all the work in place in 2024; we need just enough to maintain the flood defence need and then use local resources to progressively deliver the longer-term solution with a local benefit to the economy. This work could be collectively done by local contractors under the supervision of either the EA or the Drainage Board. There is simply no engineering need for the EA to wantonly and unnecessarily destroy our landscape when cheaper and more sustainable alternatives are available.

NB there is only an intent to continue to raise the river banks 

To put this into perspective that recycled material would

  • build a bank 5m high bank from the Bridgwater Tidal Barrier to Combwich.
  • raise the banks and build the secondary flood defences up to match climate change.
  • raise the banks, build the secondary flood defence and start building new defences north from Pawlett Hill towards Highbridge.
5m high and nearly 5 miles long, 100 years of digging house foundations

Sea Level Rise

Sea level rise is not expected to slow for at least 300 years making both the barrier redundant as the river banks can only be raised perhaps another metre before they overload the poor ground conditions of the Parrett Estuary. Ultimately the long term plan for Chilton Trinity and Pawlett Hams’s will be realised.

The continued conditioning of the population by the EA to passively accept surrender to the sea as the first option for non-London areas of the UK is disingenuous and defeatist and never mind its land we need to grow food on.

Way Forward

At £100M the present solution for the  Bridgwater Tidal barrier is clearly neither sustainable or affordable. A situation that needs to be laid at the door of the Government, Somerset Rivers Authority and specifically the EA and Sedgemoor District Council (SDC) who provide joint project oversight.  We need

  1. Sustainability in what we do is placed at the centre  of our plans
  2. An independent inquiry into how flood defence is being delivered in Somerset.
  3. A peer review of the BTB project  into how it has arrived where it has.

UK Construction; the coming change is not what people imagine

The UK Government initiatives through the Construction Industries Training Board (CITB) and the construction industry in general continues to think in terms of migrating people’s skills.

What has been apparent for a long time is that with the UK’s  an ageing population and the crutch of our cheap overseas labour being removed the time is right for the wholesale removal of people from the construction process.  Companies like Laing O’Rourke are making the investment, but the rest of the UK construction industry seems oblivious to the tsunami of change about to hit Europe.

China with its ageing workforce is already making huge strides with true OSM and it won’t be long before we see Chinese companies bringing that technology to the UK and the EU. With automated factories and sites running 24 hrs day they will slash delivery times and cost. Soon to be legalised automated driving systems means even the delivery trucks won’t need drivers or be constrained by driving hours.

If the Chinese dont drive OSM the cost of second hand manufacturing robots will. A used robot usually seen in a car factory can now be bought for £10-15k (1/3 of the annual employment cost of a semi-skilled operative) and with 60,000 hours time left in the machine that is less than 25P per hour plus operating cost. It won’t be long before the change in our process is driven from the bottom up.

A look at this advert tells you what you need to know

http://www.globalrobots.com/product.aspx?product=23064

In many ways UK construction stands on the edge of a new industrial revolution with the cost of automating construction dropping and entry levels cost being within reach of small companies and not just the largest the conditions to disrupt UK construction is well timed. It will soon be possible to create low cost production lines using second equipment manufacturing small construction elements for an investment of less than the cost of a UK house.

The CITB initiatives looks less like progress and more like King Canute. UK construction faces with the exception of maintenance being wiped out as an industry unless it changes rapidly.

Build the Bridgwater Tidal Barrier at Combwich

The option of building the Bridgwater Tidal Barrier at Combwich  was always affordable and as we now see the full whole life cost of the present scheme being made public its clear the best location was never considered.

Why Combwich?

Combwich would be a conventional location for a tidal barrier as its near the mouth of the River Parrett.  Combwich is a unique site that would offer Somerset a long term solution to protecting the southern Levels as a barrier and associated embankment would close the narrow gap between Stockland Bristol and the Polden Hills via Pawlett Hill. The location also offers an appreciable increase in the fluvial conveyance capacity of the existing River Parrett catchment river system.

COMBWICH & BRIDGWATER TIDAL BARRIER LOCATIONS

Original image is courtesy of the British Geological Society.

The yellow colour in the above image is the soft clay deposited around 11,000 years ago. The existing river banks will see the new flood defences from Combwich up to the site of the proposed Bridgwater Tidal Barrier built on this soft material that is up to 20m deep. Defences that due to settlement will need to be  built back up every 30-35 years  defending  land that will have been flooded  with saltwater. 

The argument is that it’s the cheapest solution where it is in Bridgwater. 

People continue to believe the width of the river and the length of the barrier structure is the only driving cost of the scheme. Whilst size does matter it is not all that matters. Like most schemes that start without a clear direction the final cost proves to be significantly more expensive than expected and the Bridgwater Tidal Barrier is no exception. The EA project team didn’t understand its costs just its objective. They are not the same and nor are they aligned with securing Somerset’s long term future.

Most people are aware that present scheme  originated from a 2009 scheme that was little more than a knee jerk reaction to climate change and the long-standing need for a control system in the river. What we have seen is that inexperience in project delivery saw the early focus on one element of the scheme rather than the scheme as a whole. Effort was exclusively focused  on the barrier, the type of gate and location within a short length of the River Parrett and it clouded objective thinking about  an holistic scheme. It was so bad that the EA team doing the barrier were unaware of the test bank being done by the EA and Team Van Oord;  there was simply no joined up thinking.

Nobody at  that time or since has been willing to stand back and take a cold hard look at what was needed when the Cameron Government’s political promise of post 2014 flood money removed critical thinking from the delivery process.

The simple fact is that every activity has a cost and the choice the client and the designer has is where you spend the money today and tomorrow. A simple comparison of where our money will be spent is produced below. You can spend money on lawyers and land agreements for secondary flood defences or spend the money on a better barrier. Paper does not keep the sea out.

Combwich offers a number of advantages that offset the barriers extra length and the constraints of the present location in Bridgwater. These advantages include the use of precast concrete construction, the  availability of space for construction, no need for an expensive diversion channel and the long periods when the river is empty make considerable cost savings.

The key savings are given below.

Where the barrier money goes

a barrier structure could also support a future bypass.

Barrier and replacement Dunball Wharf at Combwich

The good thing about the River Parrett and there are very few is that its possible to work on the river bed without the need for a coffer dam. If you have the space and you’re in the infrequently used navigation channel of the Parrett you move and do things in the water during high tide and then drive down the bank onto a prepared river bed. and work during low tide.

 

Bridgwater Tidal Barrier cost reaches £100M

Sedgemoor District Council  and the Environment Agency  recently reported at the Somerset Rivers Authority (SRA) meeting  in January a 50% increase in the cost of the Bridgwater Tidal Barrier. The reported cost appears to have increased from  £70M in October 2017 to £100M in January  2018  (five months) and yet it went through without comment .

The cost escalation of a scheme that does nothing to address the 2014 fluvial flood is eye watering and yet, according to the minutes, no action is taken to explain why this escalation had occurred and what action was being done to mitigate it. The mere acceptance by our elected members is not acceptable if the delivery of our infrastructure is to be managed locally rather than through central government.

Bridgwater Tidal Barrier Cost History

  1. March 2014 the cost of  barrier was reported at £26M
  2. September  2016 The EA  gave the public figures during a public consultation  various options with costs;  site 5 the selected site was costed at £45M – £60M.
  3. October 2017 the BBC reported on the cost of the scheme to be  in the order of £70M  “Bridgwater tidal barrier costs ‘could go up by £10m”
  4. January 2018  indicates the cost is now around £100M as noted below from the published SRA draft minutes.

In a period of around 15 months from September 2016 to January 2018 the cost of the Bridgwater Tidal Barrier scheme rose by around £50M or 100% and not one word of concern is  expressed or recorded in the public domain. This cost is now  nearly 4x  the original cost estimate in 2014.

Bridgwater Tidal Barrier is now a £100M scheme where

  • the financial investment makes no contribution to mitigating a repeating 2014 fluvial flood,
  • repeated saltwater flooding onto farm land from the River Parrett is seen as being an acceptable regime despite poisoning farmland and wildlife. 
  • there is no plan in place beyond the barriers  100 year design life
  • brings saltwater  onto our agricultural land

Looking at the numbers the only thing that can be concluded is that the cost estimates presented to the public and to councils for the purpose of decision making were widely inaccurate or inconsistent either of which is unacceptable for investment decisions; especially decisions that affect the long term future of Bridgwater and Somerset Levels beyond.

The selection decision of the current site (Site 5) was chosen purely on the basis of the width of the river and must now be called into question.  It would appear that the cost of the other downstream elements of the scheme must be causing this cost escalation. A cost and concern that were dismissed at the time of the consultation. 

Bridgwater Tidal Barrier is now a £100M scheme where

  • the financial investment makes no contribution to mitigating a repeating 2014 fluvial flood,
  • there is no plan in place beyond the barriers  100 year design life
  • repeated saltwater flooding onto farm land from the River Parrett is seen as being an acceptable regime despite poisoning farmland and wildlife. 
  • the EA wants to dig up the very land its meant to be protecting to win the soil  for flood defences.

No project should be seeing this amount of budgetary increase  without  challenge.  Cost escalation on this scale is unacceptable and unnecessary. There is clearly a continuing problem regarding a  lack of oversight both technically and financially in this project.

What should be done?

The extra £50M buys a much better scheme than the one Bridgwater is getting. £100M would allow

  1. the barrier to be located as is normal practice as close to the mouth of the river as possible which in this case  is Combwich. Combwich was never looked on the basis of cost, clearly that is an argument that can no longer be supported.
  2. elimination of most of the downstream river works that the EA’s tests indicate will need to happen every 35 years or so.
  3. increased fluvial capacity in the River Parrett and the King Sedgmoor Drain potentially benefiting communities beyond Sedgemoor
  4. a solution that can be economically extended beyond the 100 year design life currently offered.

£100M is £1M a year for next 100 years on scheme that will be rendered redundant once the river banks can no longer be raised to combat sea level rise; the scheme in present form is throwing money away 

The public expect that those on scrutiny committees to use there position to bring transparency  and accountability to the process of public expenditure. Such bringing to account appears to be sadly lacking together with visibility of any independent engineering review that a project of £100M warrants. The project is growing in value and the oversight is not growing with it.

Unfortunately what we see happening is the management of infrastructure projects by people, primarily councillors  and  officers who are unqualified to do so. The SRA is a prime example of an organisation primarily engaged in  the commissioning of engineering activities with no engineers in lead roles.  The Bridgwater Tidal Barrier has become a Grand Designs episode of Civil Engineering

Way forward

A  Public Inquiry  into the management  of the Bridgwater Tidal Barrier scheme should be convened that should look at

  1. Cost
  2. Management
  3. Consultation process
  4. Location  (including the examination of Combwich)
  5. Competency and experience  of councillors  and officials  to manage civil engineering works such as the Bridgwater Tidal Barrier and other SRA projects.,

 

 

Environment Agency – Landowner Information Pack

The Environment Agency (EA)  like the many  political parties with the word Democratic in  their title seems ever farther away  from what people imagine the organisation to be about. Protecting the Environment and the people seems not to be one of them if it gets in the way of its long term Parrett Estuary agenda  at Chilton Trinity north of Bridgwater.

However any doubts that the EA  doesn’t have a sense of humour or understands irony was firmly dispelled by its latest offering to the  Chilton Trinity landowners.  These are landowners whose land is impacted by downstream works  resulting from planned construction of the £100M Bridgwater Tidal Barrier close to the town rather than is conventional practice at the mouth of the River Parrett.

In March 2018 each landowner was the recipient of a document called BRIDGWATER TIDAL  BARRIER  DOWNSTREAM FLOOD  DEFENCES Landowner information Pack.

The EA’s  apparent lack of understanding of the impact of salt water flooding onto farm land. is worrying. The expected  floodwater  is not like 2014 when the water that covered the Somerset Levels was predominantly fluvial run off (freshwater). This will be seawater coming up the River Parrett from the Seven Estuary that over tops the river banks. 

This document also asks farmer’s to allow the Environment Agency to dig borrow pits in the land the EA are meant to be protecting.  Borrow Pits are meant to be refilled  with other less suitable soil so it does not lessen traffic as the EA claim but only if  they are left as  just open pits in which case they aren’t borrow pits.  Do we really need to excavate the land we are meant to be protecting?

The  alternative is a sustainable construction method that also seems to be a low priority of the EA.  Construction of the bank improvements could be phased over a number of years using local contractors and material reclaimed from new developments. 

The proposed pits will hold  the seawater (saltwater)  rather than see it quickly flushed away back to the river. Saltwater is poison to agricultural land and the habitat  we currently have in Chilton Trinity.  These  pits  will, according to the  trial embankment test done for the Cannington Bends improvement scheme, need to be reopened or enlarged every 35 years of so to make up the levels as the made up river banks settle.

The  EA promise going forward regarding maintaining bank  levels quite rightly only talks about intent; the EA cannot provide a firm promise however they do know  that once the land is poisoned the cost for further expenditure on bank raising will not be justified.

No one can say that the EA does not have a sense of humour especially when  the Chilton Trinity farmers are encouraged  by the EA to act as turkeys to vote for Christmas.  The EA’s long term ambition of an inter tidal habitat remains our pantomime villain  – he is behind us and  we chose not to look around and see him. Whilst appearing to help the EA  are actually creating a self fulfilling prophecy that will see  the area become salt marsh.

This document

  • Only talks about 2024 and not 100 years in the future (2124)  which is much more interesting for long term prosperity of everyone including our farmers handing land onto future generations. ( nobody says what happens when the banks can no longer be raised)
  • Confirms the level of protection they are planning to maintain to farm land is very low.
  • Omitted the future flood maps.
  • Omitted to  mention that the flood water will be seawater .
  • Demonstrates on page 4 a complete lack  of understanding of the impact of saltwater onto agricultural land. (Some Lincolnshire farmland has still not fully recovered from the 1953 flood when the North Sea over topped the sea defences)
  • Encourages the formation of borrow pits (actually just pits) that, when the banks of the River Parrett are overtopped, will trap seawater and ultimately destroy the value of the land its meant to protect.  Destroying wildlife and fauna in the process that cannot handle saline conditions A case of the medicine killing the patient.
  • Creates through the use of borrow pits mores areas of stagnant water that in our warming climate will be a breeding ground for insects, one of the reasons given for not damming the River Parrett.
  • Fails to mention the pits will need to be used and extended at least 3x as according to the embankment trial the river banks will need raising every 35 years.
  • Does not mention the final height of the river banks in 100 years’ time, for every metre raised the bank get wider by  2 x 4.0m and the banks will need to be raised by around 0.80m. (2’6″) excluding the continued settlement of the river banks that always means 2 steps forward and always 1 step back.
  • Re-confirms that agricultural land will be preferentially flooded.
  • The EA commitment is qualified as only an “intent” . Will SDC ratepayers pay for the maintenance when they don’t get anything back? It’s a huge liability that SDC could end up with that has no benefit to the town.  In a very short period of time, the cost of maintaining river banks to protect a small area of land and some ponds (flooded borrow pits) will not be considered worthwhile.

No one can say we were not warned about this  EA scheme and still no one asks what happens after the proposed scheme, the Bridgwater Tidal Barrier, can no longer counter rising sea levels?

One can only appreciate the irony and the humour of the situation  along with the EA’s other recent bits of entertainment

  • The   gathering up the local newt population at Steart and their subsequent disappearance
  • Diverting migrating elvers away from their normal route to our freshwater river system into the Steart Peninsula scheme.
  • Planning to build a tidal barrier as far inland and upstream as possible contrary to all normal accepted good practice.

to paraphrase Churchill

never has so much money been spent in such a small place to so little effect 

This document is at best poorly put together and at worst a device designed to obscure the true impact of the  plan from those most affected

As this slow-motion environmental, and for Bridgwater, and economic car crash occurs we should not forget that three prominent members of the Wessex Regional Flood and Coastal Committee live within a mile or so of where this unnecessary and increasingly misrepresented process is going on.  No objection or question is heard regarding the impact of the EA Scheme; there is no visible oversight.

The Internal Drainage Boards are equally silent as is the Somerset Rivers Authority

Finally, you know its wrong when that well-known litmus test is applied; The  scheme in its present form  has the support  Ian Liddell-Grainger

 

 

 

Retention of Concrete Consistency

Designing concrete mixes for specific purposes often raises questions that you don’t know the answers to. Familiar products have fallen into disuse and new products are just new. A recent project in Shetland required a mix able to get into areas of heavily congested reinforcement that had previously failed the first time around.

Highly plasticised mixes look and behave differently from “ normal “ concrete and  the current mix was  a 100% Portland cement mix that  appeared to have followed me over from Abu Dhabi with the same original contractor having developed a similar mix for two different projects. Shetland and Abu Dhabi having in common a lack of cement replacements particularly in the oil & gas industry. A situation further complicated  as  the current mix had a very high cement content was plasticised but not retarded making it very difficult to use in all but the simplest pours. It has  very little time to be placed.

The rework had a number of challenges that followed from the earlier pour.

  • Hanging shutters that obstructed the passage of concrete.
  • A relatively small volume; less than 10m3
  • Over detailing of reinforcement; surplus reinforcement that had not been removed during original  fixing.
  • Complicated shuttering and finishing that required considerable time to complete after the bulk of the concrete had been placed.

For the revised rework mix a new mix  with the following requirements was developed.

  1. A 10mm aggregate for  congestion and cover issues.
  2. Place using the chute from the back of the truck.
  3. Delay the setting time to around 3 hours.
  4. Retain the waterproof qualities of the existing mix.
  5. Characteristic strength of 35N
  6. Satisfy durability requirements for a Marine Environment.

TESTING & APPROVAL

Sika provided an S4 mix design based on the above requirement;  to obtain client approval and to understand what we had and how it worked a simple test was done twice.

Batches of the revised concrete  mix were mixed and held in a truck mixer replicating a long discharge time on site.

The truck mixer was progressively emptied over 3 hours.

Slump test were taken every 20 minutes and cubes at hourly intervals (1,2 and 3 hours) for testing at 7 and 28 days.

Testing at EMN Plant’s Scatska Batching Plant in Shetland April 2017

RESULTS

they were very good

  • the mix stayed at or round the design slump only marginally dropping off in the last two results  but still within limits.
  • cube results were consistent and all passed.

LESSON LEARNT

One important thing that was noted was that the consistency (slump) potentially drops for a short period below the specification ,about 1 hour after batching was completed, and then regains the required consistency. It occurred on both batches.

The lesson for Contractors, Consultants  and QA /QC processes is that

  • The time from batching to the initial test is important and that there is the potential to reject concrete that is actually ok.
  • When doing trial mixes develop tests that explore  what could happen when a concrete pour goes wrong and placing of concrete is delayed identifying any characteristics that might explain a rogue test result during placing operations.

 

 

Bridgwater Tidal Barrier Drop in Session 10th July 2017

On the 10th of July at Bridgwater Town Hall (2-7pm) the EA and SDC will reveal the final form of their scheme for the Bridgwater Tidal Barrier. Its construction will shape the town for the next two hundred years. It is planned to be commissioned in 2024 and designed to operate for 100 years. The operational date is a political one rather than climate driven and unlike most similar structures it will be located within the town rather than at the mouth of the river.  Mitigation of a similar fluvial flood event to 2014 is not part of the barrier’s function.

People have been focused on the barrier yet the river banks are the important bit; what happens to them will decide how radically our existing landscape will change and have far greater impact than a set of gates. The downstream river banks are being maintained in accordance with the FCERM Strategy (the national flood and coastal erosion risk management strategy for England).Individual polices are detailed in the local 2010 Shoreline Management Plan covering the next 20, 50 and 100 years.

For the Parrett those policies say that within the operational life of the barrier “The long term vision is for a more naturally functioning estuary, through construction of set-back defences under a policy of managed realignment.” Land is being returned to the tidal zone.

EA maps produced in 2010 show how that will be achieved at Pawlett Hams and Chilton Trinity. The recently released BTB secondary flood defence plan and residual flood risk maps show the long term policies are being put in place. Only the river banks close to Combwich and Chilton Trinity housing will continue to be raised. Farmland will ultimately be flooded and lost as the majority of the river banks will cease to be raised to match climate change. Steart Peninsula’s habitat will in due course be extended to Dunball and Chilton Trinity.

The present scheme means that the opportunity to increase the conveyance capacity of the Parrett capacity by moving a future replacement barrier downstream is lost. Taunton Deane and South Somerset may have to build fluvial storage on their land in the future. Opportunities for a cost effective bypass will be lost to the detriment of Bridgwater and West Somerset. As a naturally occurring event Somerset land owners will not receive compensation. Bridgwater will pay around £20m in lost land values towards the present scheme. A major economic impact on Somerset as a whole is just being ignored.

It is simply not true or credible that the BTB can somehow be divorced from the EA’s longer plan for the Parrett Estuary; a plan prepared in 2010 predating the 2014 flooding of the Somerset Levels.

The Bridgwater Tidal barrier in its present form passed its sell by date in 2014 when fluvial flooding moved from management on the Levels to flooding within our homes. Even today people still imagine that the Bridgwater Tidal Barrier is somehow part of the scheme to mitigate the 2014 flood, it could be but it isn’t. The Levels’ will still flood as they did in 2014 if we get similar weather conditions.

With little information in the public domain including the option studies that supported the original 7 location and the shorter list of 4 it is not unreasonable that this scheme has many questions of transparency.  it  is unacceptable that important and relevant information is not available to the public ahead of the final consultation on the 10th of July. That flood maps produced in September 2016 have only just been published giving people little time to understand the implications of what is planned.

If the FCERM Strategy and Parrett Estuary Flood Management Strategy are executed in their present form 1000’s of acres of agricultural land will be lost to food production. Is it morally right that the UK which cannot feed itself should export even more of its food production overseas and possibly deny food to others? This lack of responsibility on our part will no doubt be further compounded when our overseas aid budget has to be used to relieve a famine we as a nation knowingly or perhaps worse unknowingly contributed to.

To reach this situation there is a clear lack of leadership, vision, scrutiny and oversight by those organisations and people charged with delivering the plan and the infrastructure for Somerset. Neither SDC nor the SRA has any engineering or qualified staff able to lead on flooding and  has chosen not to bring in people that could. There is also a clear engineering  deficit in the delivery of Somerset’s flood defences.

People should go along to the consultation and ask

  1. Is turning the River Parrett back 500 to 1000 years and extending the Steart Peninsula wildlife habitat to Dunball whilst constraining economic development really what Bridgwater and wider Somerset need?
  2. Why wasn’t a barrier considered at Combwich and extending to Pawlett Hill that would protect the whole area. Arguments that we might impinge on the edge of the SSI is not an argument for not even looking at the possibility.
  3. Why does the barrier only do TIDAL and not  FLUVIAL (2014 rainfall) with equal importance?
  4. What is the extra cost of building a barrier with a bridge on it?

 

Steve Trowbridge CEng MICE MIStructE

 

 

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.

Policies 7d38 to 7d42

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. 

2025 1:200 Flood Return

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

 

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)

West Quay One days Tides
West Quay One weeks Tides
HPC Tide Gauge

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.

West Quay- One Months Tides

Looking along the river it could be shown

River Parrett at Low Tide

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.

Dunball Clyce (River Parrett side)

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.

River Parrett – Increasing the Flow

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