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.
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.
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.
a barrier structure could also support a future bypass.
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.