Blyth Estuary Myths, Truths, Facts and Figures

This is a summary of the Blyth Estuary Group’s response to the science which the EA claim ‘backs’ their Blyth strategy. The B.E.G have conclusively shown that the data supporting the EA's Blyth strategy is fundamentally flawed and incorrect.

Below are detailed the B.E.G's Facts and Figures as well as the Myths and Truths surrounding the Environment Agency's plan for the Blyth.

1) DEFRA One Metre Sea Level Rise (SLR)?

Defra’s recent 1 metre SLR prediction is based on the maximum projection of the highest CO₂ ‘emission scenario’ in the IPCC ‘Third Report’. The IPCC ‘Fourth Report’ released in March 2007 has substantially reduced all SLR projections. Taking an average of the six emission scenarios contained in the ‘Fourth Report’ and adding an adjustment for local isostatic land movement; the average here by 2099 will be 423mm. This is only 83mm more than our normal rise over the last one hundred years and only about 33mm of this is expected to occur in the next fifty years. The gradual increase in wall height required to track the ‘Fourth Report’ average SLR over the next one hundred years should pose no real threat to clay walls with a good access track. Currently there is no North Sea tide gauge evidence that SLR is accelerating (Van Cauwenberghe 2000). Careful measurement of the depth of Southwold Town Marsh embanked in 1630 and today’s saltings level show that Mean High Water SLR has remained constant here at about 3.4mm/yr for the last four hundred years. It is our opinion that Defra’s adherence to an outdated projection is unscientific.

2) Increasing Storm Surges?

Currently there is no Lowestoft Tide Gauge evidence that ‘storm surges’ are increasing in frequency or severity. Data from the BODC website (See appendix A).

3) Coastal Squeeze and Mitigation?
(Overall saltmarsh loss by wave erosion)

The EA claim that the Blyth is losing saltmarsh. They cite a 2000 report by Dr N Cooper of Newcastle University (commissioned by Dr C Beardall EA), which claims that the Blyth lost 6.9% of its saltmarsh between 1971 and 1998. However Dr J French of UCL, who must have used the same or similar aerial photos, concluded in his 2003 report that saltmarsh had increased over the same period by 16.1%. Careful examination of the photos used by Dr Cooper (held by Suffolk Records Office) show much of the area lost was either not saltmarsh in the first place (e.g. the eroding hillside at Bulcamp Old Marsh) or was low saltmarsh covered by a spring tide appearing to be mudflat. Where saltmarsh loss is identified NE require ‘mitigation’ (The imposed breaching of marshes to offset the area lost to erosion).

4) Increasing Tidal Prism?
(Rising water volume and river flow due to sea level rise outpacing sedimentation)

The results of a ‘one month’ ADCP suspended sediment survey conducted in June 2003 were interpreted by the EA’s consultants Black & Veatch as confirming a claim made in 2001 by Dr Jon French UCL that there was little or no sediment being deposited in the estuary. This interpretation led to entry of ‘zero sedimentation’ into the estuary model which increased the tidal prism and river flows by 63% with an SLR of 0.6m by the year 2100, making the existing clay walls unsustainable. The ‘Independent’ review group that approved this entry comprised Dr Jon French (University College London), Dr Roger Morris (Natural England), Karen Thomas (Environment Agency), Dr Greg Guthrie (Royal Haskoning) and Dr David Keiller (Black & Veatch). Those who know the estuary well, find the claim of ‘zero sedimentation’ patently absurd. The Blyth Estuary Group BEG was formed to investigate the EA’s science and discover new evidence. BEG core samples, 137Cs and historical sedimentation analysis show that average mudflat sedimentation here is about 11mm/yr and is outpacing sea level rise by a comfortable margin of 7mm/yr. This has reduced the tidal prism and river flow by 18% since 1950 and will reduce the prism and river flow by about 23% over the next one hundred years (See appendix B). Note. ADCP acoustic back scatter equipment is wholly unsuitable for the measurement of fine clay sediments of less than 120 microns as deposited on our mudflats.

5) Exhausted Sediment Supply?

The EA claim our sediment sources are exhausted. The main sources for the Blyth mudflat accretion are 5.2Km of eroding cliffs (average height 7m) and 6.2Km of eroding shore and offshore clay deposits (down to 10m) at Benacre (4.7m/yr), Covehithe (4.3m/yr) and Easton Bavents (2.6m/yr) and 2.3Km of eroding submerged clay deposits (down to 5m) in Dunwich Bay (1m/yr). Total eroded clay sediment (based on 33% clay content) is about 210Kt/yr – About 18% of this volume is deposited each year in the Blyth. Currently there is no evidence that this erosion is slowing. Indeed should SLR accelerate as predicted by the EA, coastal erosion will accelerate leading to an increase in sediment supply. The (m/yr) figures are the average losses since 1891.

6) Ebb Dominance? (Net tidal sediment loss to the sea)

NE claim our estuary is ‘ebb dominant’ and therefore losing deposited clay sediment to the sea, however this is not supported by the ADCP flow survey slides presented by Black & Veatch to the BEG meeting in June 2006. These show the tidal flow to be 4.8% ‘flood dominant’ at Reydon close to the mudflats (See appendix C).

7) Clay Wall Death?

The EA inform us that our four hundred year old clay walls have reached the end of their life. Certainly ‘end of life’ is close, since in the hands of the EA they have received no proper maintenance for forty years. There are many areas that are over 0.3m below a 1 in 10 year flood level and without proper maintenance soon, this one will certainly become true. NOTE. Clay walls with a 1.5m crest and a 1 in 1 slope that are used as footpaths naturally slump about 10mm/yr (e.g. Tinker’s and Delacroix). The height of these walls has always required regular maintenance.

8) Unsustainable Walls?

The EA claim that our four hundred year old clay walls are unsustainable because they would ‘collapse’ if raised to 2.7mOD. However, some fifty years ago their predecessors successfully raised the clay wall at Blackshore, built in 1630, protecting Southwold Town Marsh and the Ferry Road properties, to a height of 3.1mOD.

9) DEFRA’s 100 Year Defence Standard.

This may be fine for hard defences but wholly inappropriate for clay walls. The beauty of clay walls is that, with a good access track, they can be inexpensively raised or retreated to meet what ever threat is encountered.

10) Tinker’s and Delacroix Marsh Wall Breaches.

During the ‘storm surge’ of November 9th 2007 Tinker's and Delacroix Marsh wall was breached in 10 places totalling 110m. All the breaches occurred where the walls were overtopped by more than 0.2m and where the landward wall slope was about 1 in 1 or less. Without repair soon the breaches will erode increasing the river flow by 22% and this will have a very serious and detrimental effect on the infrastructure and safety of navigation in Southwold Harbour – a Haven Port since 1489. The EA have refused repair claiming "We do not accept that there is any damage caused by us that needs to be put right".

11) The EA "Defence Level".

On January 24th 2007 Nigel Pask EA confirmed in an email to us that their 1 in 10 year ‘Defence Level’ for the walls upstream of the Bailey Bridge was 2.26mOD raising to 2.28mOD at Wolsey Creek. Sadly had they been maintained to this level no breaches would have occurred.

12) Permissive Power.

The 1991 Water Resources Act removed the EA’s responsibility for maintaining the height of the defences. Unfortunately this fact was never made clear to the landowners who were repeatedly promised that when funding became available remedial work would start. One landowner was so concerned about the state of his defences that he started the work himself. This drew instant threats from the EA and he was forced to stop.

13) Definition Of Maintenance.

The EA define ‘maintenance’ as "undertaking works to minimise deterioration of a defence from its current condition". ("Withdrawal of Maintenance Policy" EFD 07/59 dated 19/10/07)

A maintenance regime that permits continuous deterioration of clay defence to a point 250mm below the known storm levels and to failure can only be described as negligent.

A Google Search of ‘maintenance’ produced a rather different definition from the Environment Agency's. ‘The European Federation of National Maintenance Societies’ states "All actions which have the objective of retaining or restoring an item in or to a state in which it can perform its required function. The actions include the combination of all technical and corresponding administrative, managerial and supervision actions".

14) Withdrawl Of Maintenance.

This is of course a misnomer. Proper maintenance was withdrawn many years ago - what the EA mean is a withdrawal of damage repair work. Normally the EA would give two years notice of withdrawal; however where the damage is significant as in the case of Tinker’s Marsh, maintenance is withdrawn without notice.

15) Buss Creek Flood Relief Wall.

In 1960’s the EA’s predecessors built a 200m concrete Flood Relief Wall with a top height of 2.5mOD at Buss Creek to protect the estuary clay walls from breaching during a storm surge. This fine structure is only effective however providing the estuary walls are maintained to a higher level. Sadly the walls at Tinker's and large parts of Reydon and Hen Reedbeds have been allowed to deteriorate to 0.5m below this level.

16) Estuary Group Plans For Wall Reinstatement.

To date we have been unable to persuade the EA to reinstate our clay walls so we have embarked on a ‘contingency plan’ to do the work ourselves. We propose to rebuild the walls to a level which will again make the Buss Creek Flood Relief Wall an effective structure (2.7mOD upstream and 2.8mOD downstream of the Bailey Bridge). We will do this by applying to the EA and NE for Land Drainage Consent and Waste Soil Exemption Certificates to build 8km’s of 12m x 1m wall access tracks. New soak dykes will be excavated landward of the tracks and the excavated clay will be used to rebuild the walls. The revenue generated by the waste soil disposal charges will fund the project.

NOTE. The clay walls for reinstatement in the ‘contingency plan’ are Tinker’s, Delacroix, Hen Reedbeds, Reydon, Robinson’s and West of the A12.

CONCLUSION

It is clear that without a statutory duty to maintain the height of the defences and the use of a debased definition of maintenance, the EA’ have delivered 10 defence breaches to a protected SSSI, SPA and Ramsar site at Tinker’s and Delacroix Marshes.

Many hundreds of metres of the defences have been allowed to deteriorate over the last forty years to a point 0.25m below the EA’s own 1 in 10 year ‘Defence Level’ - and all without mention to the landowners. The instant ‘withdrawal of maintenance’ faced the landowners with the removal of 300,000 cubic metres of sea water before they could exercise their right to maintain the defences themselves.

The repairs to Tinker’s and Delacroix marsh walls are of paramount importance to us for if this is not done soon the Blyth tidal prism and river flow will increase by 22% and this will have a very serious and detrimental effect on the infrastructure and safety of navigation in Southwold Harbour. Once Tinker’s wall and saltings have eroded, the Reydon defences would come under increasing wave attack by the prevailing south westerly winds leading to their eventual failure. The resultant river flow (+103%) would then destroy Southwold Harbour. We must not let this happen.

ACKNOWLEDGMENTS

The Group would like to thank Philip Kett for providing the invaluable James Walker 1840 Blyth Estuary Report and many historical maps and documents and together with Paul Hashim, for venturing out onto the mudflats to collect core samples and those who assisted in the placement of over 350 reference posts in the estuary walls and the collection of the GPS height data. Also the EA for supplying the 2003 LIDAR data, Dr Alan Thompson Cuesta Consulting for technical assistance and our ‘Position Paper’, Stuart Boulter SCC for supplying aerial photos and John Huggins and Adam Burrows NE and helpers for sandbagging Tinker’s ‘main breach’ and many others who provided helpful comments and support over the last two years.

APPENDIX

Appendix A – Storm Surges over 2.5mOD since 1964

Storm Surges over 2.5mOD since 1964 Lowestoft BODC

No.	Date	mOD	Duration (hours)
1	29/09/1969	2.71m	9
2	03/01/1976	2.68m	19
3	01/02/1983	2.69m	9
4	21/02/1993	2.64m	19
5	09/11/2007	2.63m	19

Appendix B – Estuary Sedimentation since 1950

Area	(a)	(b)	(c)	(d)	(e)	(f)
1) Sandpit Marsh	0.76m	0.26m	-0.46m	0.56m	32ha	0.24Mm3
2) Angel Marsh	0.61m	0.55m	-0.46m	0.70m	34ha	0.29Mm3
3) BC New Marsh	0.91m	0.09m	-0.46m	0.54m	43ha	0.18Mm3
4) BC Old Marsh	0.69m	0.25m	-0.46m	0.48m	61ha	0.23Mm3

• a) Walker 1840 Survey differentials.
• b) EA 2003 Lidar ‘mean’ mudflat elevations. (Prof. K. Pye)
• c) EA/Walker difference less MHWS. The difference is calculated from the average of the EA 2002 marsh transect ‘mean elevations’ for the two adjoining marshes (Tinker’s & Reydon) and the Walker 1840 survey ‘marsh elevations’ referenced to today’s MHWS level of 1.1mOD. [(0.65m + 0.63m) /2] – 1.1 = -0.46m. (Prof. K. Pye)
• d) Average Mudflat Sediment deposition.
• e) Mudflat Area. Total 170ha (J. French).
• f) Sediment volume. Mm³ (Million m³). Total 0.94Mm³
• • Average mudflat sedimentation since breaching:–
    0.94Mm3 / 170ha = 550mm over approx 50 years ( 11mm / year ).
  • Average yearly sediment import to mudflats:–
    (0.94Mm3 / 50) x 1.6sg = 30.1Kt/yr.
  • Average yearly sediment import to other areas:–
    (325ha – 170ha) x 3.4mm/yr SLR x 1.6sg = 8.4Kt/yr.
    Total average yearly sediment import:–
    30.1 + 8.4 = 38.5 Kt/yr. (An average of 55t per tide).

Appendix C – ADCP River Flow Survey showing 4.8% ‘Flood Dominance’ at Reydon