Tyndal research paper into Offshore Aggregate induced Erosion

In the hope of getting some meaningful empirical research performed that would conclusively prove the impact that Offshore Aggregate Dredging is having upon our coastline, MARINET wrote to Mike Walkden and P.K. Stansby, authors of Tyndal Working Paper 97 ‘The effect of dredging off Great Yarmouth on the wave conditions and erosion of the North Norfolk Coast’, a paper study that concluded with “No significant difference was found in the nearshore wave climate or the shoreline erosion due to the dredging scenario”.

As it provides many of the contentions that MARINET has with the Crown Estate licensing authority, , the MMO, the EA and BMAPA, the dredging association(s), etc. we publish it here so that objectors to proposals to issue further dredging licences may use parts of it in their own responses.

 


 

Subject: Tidal Working Paper 97 ‘The effect of dredging off Great Yarmouth on the wave conditions and erosion of the North Norfolk Coast” by Mike Walkden and Peter Stansby at www.tyndall.ac.uk/sites/default/files/wp97.pdf

Our MARINET team are concerned at the conclusion reached in your Tidal Working Paper 97 from which the abstract deduction was “No significant difference was found in the nearshore wave climate or the shoreline erosion due to the dredging scenario”.

Our findings, based on our own and others research, practical investigations and correlations are that dredging the seabed for offshore aggregate between four and twelve miles offshore between Winterton-on-Sea and Lowestoft has brought about severe beach sand loss and consequent undermining of the natural dune defence from Happisburgh in Norfolk down to southern Suffolk. Further, it has more recently been shown to be the cause of critical erosion of the Scroby Windfarm cables and tower supports.

Much damage has resulted by the loss of coastal housing, nature sites, tourist amenity, popular seaside beaches and coastal sited trade, particularly due to the denial of sea defence funding and the restrictions imposed by the Shoreline Management Plan.

This basic cause of the escalating coastal and protective offshore sandbanks has long been a bone of contention between MARINET and DoE, DEFRA, MFO, and The Crown Estate, the British Marine Aggregate Association, etc when objecting to the issue of licence applications to further dredge in this area, as despite the abounding evidence they still maintain that the removal of many hundreds of millions of tonnes of sand and shingle offshore the stricken area is not the cause of the damage.

Licensed aggregate dredging areas offshore to Great Yarmouth

Licensed aggregate dredging areas offshore to Great Yarmouth

MARINET invites you to read some of our responses to applications to further dredge aggregate, which can be seen on our website at:

Marinet responds to new Marine Aggregate licence applications for Great Yarmouth Areas 242, 361A/B/C and 328A
Marinet responds to new Marine Aggregate licence applications for Great Yarmouth Areas 401/2 A/B
Marinet asks MMO to examine the validity of E. Anglian “wave model” for offshore aggregate dredging licences
Marinet responds to new Marine Aggregate licence applications for Great Yarmouth Areas 212, 240 and 328 B/C

Our findings are that the MFA and their predecessors have, like you, employed as a basis the HR Wallingford data which uses computer modelled data rather than actual empirical data, and have ignored the findings of numerous astute bodies such as those given in our article Scientific Studies from around the world on the erosion resulting from offshore sand and gravel dredging. In particular, the Sandpit Study and the Eurosion Report.

We would wish to emphasise that the HR Wallingford data is not based upon empirical findings, but on upon simulated modelling without practical topical findings back up. The only evidence of any actual practical metering can be found in HR Wallingford’s 2004 Wave Model, but this is now ten years outdated. This study employed wind modelling not taken at the dredging site but at the shoreline, where conditions can be very different. Furthermore, it was performed at Southwold, this well to the south of the dredging and the seriously eroded shoreline area, where the offshore seabed is without a sand bank system is very different. H.R. Wallingford (in their Southern North Sea Sediment Transfer paper) tested only this one “cell” at a far southerly remote particular point on the East Anglian coast, yet produced a model for the entire coastline including the Great Yarmouth area. Once erroneous/incorrect data are introduced into computer models/simulations errors are magnified and incorrect conclusions can be reached. We feel that this is such a case.

We find that no account has been taken of the movement, collapse or growth of under sea features (bathymetric data) between the “swash zone” at the coast and the dredge areas which will influence the “wave climate” both near and off-shore. In your paper it is given that “before and after dredging the bathymetry was assumed to be static”. We consider it vital that assumption and inconclusive stale data needs to be backed up and updated with empirical data.

MARINET has gone through your paper and references and found that this study is dated 2006 and uses the HR Wallingford study (wave model) dated 2004, the self same data as we are complaining to the MMO about.

You might wish to read my briefing on the subject at www.marinet.org.uk/campaign-article/marinet-briefing-paper and our correspondence with the MMO at www.marinet.org.uk/wp-content/uploads/Areas-242-361ABC-and-328A-Marinet-to-MMO-13-Oct-13.pdf

You may also wish to read Prof. Vincent May’s paper on Dredging and Coastal Erosion which can be read by going to www.marinet.org.uk/campaign-article/why-are-our-beaches-eroding-coastal-zone-07-paper This shows the debate between the industry and public perception.

A further paper on dredging and the shoreline impact was published in Vol.130, No.6, November/December 2004 pp.303-311 of the Journal of Waterway, Port, Coastal and Ocean Engineering. It is entitled ‘Nearshore Impacts of Dredging for Beach Nourishment’. The group of researchers introduced a methodology for predicting the impacts of nearshore dredging on the coastline by using numerical models for waves, currents, and shoreline change made from validated empirical data calculated from three locations of bathymetry, wind inputs, tidal changes, etc.to show the wave transformations resulting. The calibrated model was then put to use to predict impacts of dredging on long-term shoreline change. Results reproduced observed trends of erosion and accretion along approximately 90% of the shoreline.This paper may be seen in full at:

http://cedb.asce.org/cgi/WWWdisplay.cgi?143919
and
http://ascelibrary.org/action/showAbstract?page=303&volume=130&issue=6&journalCode=jwped5

‘Effects of Marine Sand Exploitation On Coastal Erosion and Development of Rational Sand Production Criteria written by Emre N. Otay, Paul A. Work and Osman S. Börekçi can be seen at www.marinet.org.uk/wp-content/uploads/MarineSand.pdf

It tells how such mining yields an inexpensive source of sand for construction or industrial use, how it may modify nearshore wave conditions, create erosion and deposition rates, impact the sediment drift and alter benthic habitats and nearshore circulation. The goals of the project described in the proposal are to quantify the influences of sand mining on nearshore waves and currents, assess the magnitude of any mining-related erosion, and the need to establish guidelines for acceptable mining rates and locations. The conclusions are based on numerical model results, but with validation of some aspects of the modelling via field data, and how although the findings are site specific, the methodology could be applied at any coastal site that features primarily non-cohesive sediments. It further shows how regardless of the final destination of marine sand, topographic changes caused by underwater dredge holes have immediate effects on nearshore waves and currents and that these hydrodynamic changes can rapidly lead to local perturbations in the ambient littoral transport patterns and eventual changes in the shoreline morphology.

The Crown (Marine) Estate (who provide the dredging licences) have produced a detailed paper on the Norfolk offshore sandbanks describing the rather complex details of the offshore banks and the current state of knowledge on their formation and movement. The paper contains plethora of historical data and information relating to the tide and sand movement, rich in charts and diagrams, but rather thin on actual empirical evidence. It explains the otherwise apparent anomalies of the currents and tides around the Norfolk offshore sandbanks through history, and may be seen in full at www.marinet.org.uk/wp-content/uploads/Crown-Estate-paper-on2-150×91.jpg

It establishes the link between offshore aggregate dredging and sandbank and coastal erosion, to be seen under the following sections:

3.5.3 Great Yarmouth Banks

The Great Yarmouth Banks lie sub-parallel to the modern Norfolk coast. The most nearshore of these banks appear to be attached to the shoreface at the location of small headlands, known locally as nesses. Thus, Caister Shoal extends northwards from Caister Ness, and Holm Sand is attached to Lowestoft Ness. The nearshore banks are smaller, much more closely spaced and are generally set much higher in the tidal frame (and are in places inter-tidal) than the more offshore banks. Banks are between 4 and 15km long, 1.5 to 3km wide and are mostly between 10 and 20m high above the surrounding sea floor. Sandbanks such as Holm Sand and Scroby Sands may have much shallower depths on their landward margins than on their seaward sides which are prone to breaking waves. The nearshore banks such as Scroby Sands are within 2 to 3.5km of the modern coastline.

It established the physical connection between the near shore banks (e.g. Scroby Sands, close to the dredging sites) and the actual coastline. Thus migration of sand from the coastline is going to these sandbanks. Hence, as we have erosion of these offshore sandbanks due to aggregate dredging, we have a direct link to coastal erosion itself. It gives evidence of a dynamic link between the inner sand banks and the outer sand banks i.e. a transfer of material.

The Crown Estate paper further states:

3.8 Great Yarmouth Banks formation

Another notable feature of the Great Yarmouth Banks is that they are interlaced with flood and ebb channels, as identified by Robinson (1966). Two features are particularly notable. First, the main flow direction is west north west to west south east along the North Norfolk coast to the north of the Great Yarmouth Banks and north north east to south south west along the Suffolk coast to the south. Consequently, the location of the Great Yarmouth Banks is a turning point for the tidal flow. Secondly, the ebb and flood channels cut through the banks at relatively regular intervals, forming what appears to be a series of meandering channels that cross each other at each end of the bank.

Finally, the following observation is made by models which seek to explain offshore sand bank formation:

5.1.4 Model 1.4

The Great Yarmouth Banks are a sink for cliff erosion that is transported to the area by littoral drift and nearshore residual drift.

MARINET therefore feels that there is substantial evidence here in this report to present to the MMO, which suggests that coastal erosion is linked to aggregate dredging. Firstly, increased wave height due to reduced sand banks (greater depth of water allowing larger waves to form) is working in conjunction with excavation offshore (dredged sites) which are being in-filled by sand from adjacent sandbanks which, in turn are linked to each other in a chain which ultimately leads back to the coast. Thus sand eroded from the coast is ending up in dredged sites, aided and abetted by a process that requires sand in order to replace the sand that has been excavated.

MARINET would wish to see a scientific study examining, on a historical basis, the correlation between dredging levels and timings in the offshore area and beach coastal erosion measurements, with empirically based erosion measurement for both before and since dredging commenced. We believe that all the scientific evidence for this particular study exists, and it simply requires commissioning as part of the Environmental Assessment (EA). If no such correlation is exists then and only then will the dredging companies have evidence to support their claim that no link between dredging and the shoreline erosion exists, and they can be absolved.

Secondly we require a scientific study of whether there is any measurable transfer of sand from the beaches where erosion is occurring to the offshore dredging sites. Such a study is simply and easily performed by means of tracer material placed on the adjacent shoreline beaches, and its movement monitored and recorded over a period of seven years following offshore dredging. This technique involves pre-existing established scientific practices, and has already been undertaken successfully elsewhere, e.g. Fylde coast, Lancashire) and in the USA. The UK dredging companies maintain that there is no movement of material from the beaches to the dredging sites, so this study would confirm if the dredging companies or are correct in their presumption or otherwise. It is to be noted, with emphasis, that such a tracer study has never been done by the aggregate companies for the east coast, and has never been required of them by the government and its licensing agencies.

Thirdly we feel that the EA/MMO must review the assumptions built into the computer modelling which informs the REA with regard to the offshore wave regime. The offshore wave regime and the height of waves arriving on the beaches is a key factor in coastal erosion. If the seabed is deepened by removal of the offshore seabed, the wave regime can be intensified and cause increased coastal erosion. Further, especially under storm conditions such as experienced in April and early December this past year, when the beaches were taken allowing high waves to undercut the dune defences, this in turn destroying many coastal dwellers homes.
A number of points of issue and questions were raised in our MARINET meeting with EMU (the Anglian Offshore Dredging Association AODA consultants) that jointly established the vital need of meaningful tests and realistic Environmental Impact Assessments to be employed before a licence to dredge was issued, but these were all finally shunned by the dredgers.

After over a year of awaiting a response, hopefully an agreement, AODA finally indicated that they would continue as before without implementing or taking into consideration any of our needs, or positively answering any of our questions. Our points and questions put to AODA through EMU included the following:

  1. How is it that only the partisan claims of those selected by, appointed by and paid by the dredging companies themselves are considered when a dredging licence is sought, whilst the copious reports from non-aligned international expert bodies evidencing and recognising the erosive impact
    remain ignored.
  2. Why is no second opinion permitted when considering granting licences for offshore aggregate dredging when the view of the body selected by the dredging company conflicts with wider and well established independent findings? A second opinion from a non-partisan party, financially unlinked, should be permitted as well.
  3. Why do the Environmental Impact Assessments continue to employ data based upon computerised outputs made using inputs of models created from speculative and assumed data rather than actual empirical findings? Why have these modelled claims been made without testing them against meaningful and realistic empirical findings?
  4. Why have BMAPA and AODA consistently refused to carry out a sand-tracking study of material transported from the eroding coastlines to the dredging site voids in order to reveal the actual mobility and transport of the original shoreline material?
  5. Why are Aggregate Extraction Licences Environmental Impact Assessments (EIA’s) issued without any attempt to evaluate the movement of offshore sand which feeds the coastal dune system? (Recent examples are EIAs issued for Area 457 Liverpool Bay and Areas 401/2 and 202/436 off Great Yarmouth. Such omissions of data obviously reduce ability to anticipate the effect extraction will have on the neighbouring coast, and therefore fail to protect the coast from erosion. Currently the EIAs do not track the sand lost from our shoreline, do not employ topical current data and neither do they perform practical empirical research. They only rely upon assumed data. We asked that they recognise the correlation between dredging and erosion, but this point was declined to be considered by AODA).
  6. Why do Suffolk Coastal District Council, Halcrow, The Environment Agency, DEFRA, The EA, MMO, The Crown Estate, AODA and BMAPA combined still maintain that massive dredging operations are not responsible for coastal erosion when there exists not a shred of evidence to support that claim?
  7. Why have no significant and meaningful post-dredging impact studies been carried out following dredging, particularly cumulative mass dredging of multiple associate areas of the offshore seabed?
  8. On what basis do DEFRA and the dredging companies ignore the copious independent international evidence that offshore aggregate dredging is responsible for coastal erosion? Even on the most simplistic basis is it not blatantly obvious that digging extensive deep holes offshore will promote gravitational tidal assisted sand movement from higher level areas, e.g. coastal deposits, and so steepen the shore profile, and therefore lead to beach draw-down and coastal erosion?
  9. Why is there no attempt to look for, and to sponsor, significant research that would show up the causal connection between dredging and
    coastal erosion?
  10. Is it not now generally accepted that Halcrow’s 1992 predictions for the sea approach over the Norfolk coastline covering 60 years, i.e. up to
    2052, were underestimated by a factor of twelve, the forecast lines of approach given having already been crossed within 5 years? Is it not that
    this error was the consequence of Halcrow’s failure to take into account the effect of aggregate dredging off the coast? When the impact of dredging is
    taken into account, do not the actual coastal loss figures closely agree with this and so become fully explainable?
  11. Why do the Dutch use aggregate dredged off our coast, but ban dredging at similar depths and distances from off their own? Is it not because they evaluate and understand the damage to sea life and coastal erosion caused?
  12. Why is it that dredging off our coastline continues and additional dredging sites are being sought offshore to Norfolk and the Humber when BMAPA announced three years ago that the deposits on the East Coast were exhausted and that these areas would be abandoned in favour of the South Coast and Channel sites? Is it not apparent that these ‘new findings’ off Great Yarmouth and Southwold have been deposited by migration of material from the beaches, dunes, soft sand cliffs and protective sandbanks of the East Anglian and Humber coastlines?
  13. What influence on coastal shoreline stability do you feel is contributed by the loss of beach and seabed cohesivity due to the decreasing ratio of
    the coarse granular sand removed and that of non-cohesive ‘soft sand’ dumped overboard in dredging operation?
  14. Have BMAPA and the dredging companies considered the implementation of the Dutch idea of sub-seabed suction extraction so less destroying the surface fauna and flora in order to assist stability and retain the existing eco-system?
  15. In the absence of government reimbursement of losses brought about by those losing their housing, businesses, income and amenity, have BMAPA considered overwriting these losses with a fund built from the considerable profits of their companies?

MARINET asserts that if all these questions were satisfactorily answered, then, and only then, would the dredgers be able to make their case and establish their claim that the considerable escalation of erosion has not been brought about by their activities.

A further thing we want the MMO to note is that, in the case of dispute, a second opinion from a non-partisan party, financially unlinked, should be permitted as well.

Then we need an undertaking to perform some tracer labelled sand-tracking investigation to quantify the transfer of sand from the beaches where shoreline erosion is occurring due to the offshore dredging, as performed on the Fylde Coast, Blackpool, etc.
Then there’s the need to back up the modelled claims of AODA and the assumptions evolving with practical empirical evidence to qualify them to what they claim — if they can!
MARINET is highly critical of the MMO seemingly to automatically grant offshore aggregate dredging license applications when the applicants EAs/EIAs indicate a serious lack of evidence on the likely shoreline erosive impact and the sea floor viability. The studies are currently composed by bodies who are sought for, located by, appointed by and paid for by the dredging companies themselves. Thus they cannot be seen as being independent in their findings.

Approvals for applications are being granted using information given by long outdated computer simulated information from non-relative distant points, ignoring the wealth of researched findings from other non-aligned independent scientific bodies and their practical findings. And no second opinion is permitted.

To have meaning and acceptability the EIAs submitted should employ up to date meteorological data taken over the area of dredging and the adjacent coastline itself and so study the pre-dredging and post-dredging impact to the resultant shoreline and seabed prior to commencement, ongoing for up to three years after the dredge. The cumulative effect needs also to be considered.

The studies should contain a sand tracking survey using beach strewn mildly radioactive sand particles or fluorescent beads in order to show the import and export of beach material to the dredged pits and the sand and shingle movement before and after dredging operations.

The increasing erosion of our East Anglian coast has now reached serious proportions, with housing, businesses, amenity, the wildlife sites and the coastal tourist trade suffering severe loss. The loss of shoreline and beaches correlates powerfully with the timings and levels of aggregate extracted.

MARINET is in the hope that you may wish to consider offering a valuable project on shoreline sand transportation to your students and that any further research you perform will take these points for consideration. We would welcome your response.


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