Are DEFRA Predicitions of Sea Level Rise Wrong?

In an earlier post, Are Sea Levels Rising – You Can Check Using Simple Arithmetic, I compared the observations of sea levels at Felixstowe with the DEFRA 2006 predictions.

The trend at Felixstowe is falling, so here are the graphs for Felixstowe and Lowestoft. Lowestoft has the largest rate of rise that I have seen for East Anglia and possibly UK. However the trend line is clearly less than DEFRA 2006 predictions and the observations of sea level rise show no indication that the rate of rise is accelerating, as predicted by DEFRA in 2006.

All the data comes free from www.psmsl.org

The green dots are the actual observations. The lower black line is the trend line.
The upper curving line is the DEFRA 2006 predictions. For some reason even though these predictions were published in 2006 they start from 1990. This allows us to compare how the predictions match observations from 1990 until now. If there is a major difference this means the predictions are wrong and any plan based upon them should be reexamined.

flxstwe_proj lowestoft_proj

The DEFRA 2006 predictions matter as DEFRA, who are the paymasters of EA, demand that EA uses these figures for the Shoreline Management Plan, how EA will look after the shorelines for the next 100 years.

What is really strange is that the SMP was not sent for approval until 2010, but in 2009 DEFRA issued updated predictions of sea level rise which are lower than the 2006 predictions. There are 3 versions of the 2009 predictions High, Medium and Low.

Again the DEFRA 2009 predictions start from 1990, which means we can compare them with what has actually been observed since 1990.

DEFRA 2009 predictions

flxstwe_2009proj lowestoft_2009proj

 

It is clear that

  1. The predicted acceleration in rate of sea level rise has been significantly reduced.
  2. The trend at Lowestoft is still lower than even the “Low” DEFRA 2009 predictions.

Table of DEFRA 2006 Predictions Of Sea Level Rise

Time Period
Annual Sea Level Rise
Total Period Sea Level Rise
1990-2025
4mm/year
140mm
2025-2055
8mm/year
255mm
2055-2085
12mm/year
360mm
2085-2115
15mm/year
450mm
Total Rise 1990-2115
1205mm

Table of DEFRA 2009 Predictions Of Sea Level Rise

Sea Level Rise From 1990 To
High
Medium
Low
2000
35mm
30mm
25mm
2010
73mm
62mm
53mm
2020
115mm
92mm
82mm
2030
160mm
135mm
114mm
2040
208mm
175mm
148mm
2050
258mm
218mm
184mm
2060
314mm
263mm
222mm
2070
372mm
312mm
263mm
2080
433mm
363mm
305mm
2090
497mm
416mm
350mm
2095
531mm
444mm
373mm

Observed Average Sea Level Rise

Location Observered Rate of Sea Level Rise/Fall Total Rise/Fall 1990 to 2115 Total Rise/Fall 1990 to 1995
Felixstowe
-0.2 mm/year
-25mm -21mm
Southend
1.2 mm/year
150mm 126mm
Lowestoft
2.4 mm/year
300mm 252mm

The “High” rate of the 2009 predictions is about 1/2 the 2006 rate. The “Low” rate of 2009 predictions is about 50% higher to what is observed at Lowestoft and nearly three times what is observed at Southend, let alone Felixstowe.

 

The rate of sea level rise matters for the success of failure of any attempt to create salt marsh such as the project at Devereux Farm.

Saltmarsh has to be above the water for most of the tide, possibly being covered at High Water in Spring Tides. If saltmarsh is covered by sea water for an extended period of time it will die and turn into mud flat.

The sea is murky in this area as it contains mud particles or sediment. This mud or sediment is deposited on the mud flats and saltmarsh causing them to rise vertically.

So for the saltmarsh to survive it is crucial that the sedimentation rate (the speed at which mud is deposited on the saltmarsh – hence the rate that it rises) is at least as great as the rate that sea levels are rising.

As far as I know there have only been two serious studies of sedimentation rate in East Anglia, at Tollesbury and the River Blyth. Both found a rate of about 9mm/year. This suggests that according to the DEFRA 2006 predictions any saltmarsh created would start to die out around 2055, in 44 years time.

And how long will it take to establish the saltmarsh?

Is it really justified to breach the sea walls to create saltmarsh for less than 45 years?

All the flavours of DEFRA predictions show the rate of sea level rise accelerating.

Is there any evidence that the sedimentation rate will accelerate. Or has ever accelerated anywhere?
If not bye bye Salt Marsh.

BUT

If

  1. the rate of sea level rise is low enough for salt marsh to be created and continue to live, observations suggest that this is clearly the case
  2. and the rate of sea level rise does not accelerate, and there is no evidence that it is

Then there is no need to flood any farm land to recreate Salt Marsh.

In other words the two options for this plan are

  1. It will not work.
  2. It is not necessary.

Finally to quote from Charles Beardall’s last letter to me

….Over a period of decades it is expected to fill and saltmarsh will become established in the same way as has been observed at existing managed realignment sites. As you rightly say, if sea levels rises very rapidly in future, these new saltmarshes may eventually be submerged and become mudflat. We would not expect this to occur for a number of decades, but whether the saltmarsh will still be there in 50 years we cannot say with any certainty.

Are you happy for this project to go ahead at a cost of around £1million?

It has been estimated that across the UK the cost will be £2.6billion.

This entry was posted in DEFRA, Devereux Farm, EA, Sea Level, SMP. Bookmark the permalink.

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