Tuesday, 13 October 2015

Sidmouth Beach Management Plan: finalising the reports

The Beach Management Plan steering group has been meeting over the past months:
Futures Forum: Sidmouth Beach Management Plan: documents assessing flood and erosion risk now on-line
Futures Forum: Sidmouth Beach Management Plan >>> now at Stage 3 of 6 >>> reviewing the reports >>> possible recommendations out by September

It met again this afternoon.

Here is the report from the Vision Group's representative on the steering group:

Sidmouth Beach Management Plan meeting 13th October 2015

Update by Jo Frith

Vision Group for Sidmouth representative on the Steering Group.

The Steering Group of the Sidmouth BMP project met today. The main aim of the meeting was to finalise the baseline reports for Sidmouth. These cover: Environment, Coastal Processes, Economics and the Coastal Defence Assessment.

These reports give the basis for understanding what is going on along Sidmouth’s coastline. They are an essential first step before any options for improved defences or beach management can be assessed.

Some of the key findings in the reports have been queried extensively by members of the Steering Group. The main points of concern are:

1.      The consultants (Halcrow) state that the effectiveness of any coastal defence is largely dependant on the quality and extent of the beach to calm waves down before they hit cliffs or sea walls.  They feel that the shingle in front of the town beach is now largely contained within “pocket beaches” formed between the groynes and headlands. They also feel that the shingle on the west beach is similarly enclosed. Members of the SG disputed this. They said that Budleigh Salterton is losing large amounts of its beach due to eastward littoral drift under the influence of SW storms and might be settling on the west beach. They also said that Beer beach has increased very significantly and locals blame this on losses from Sidmouth’s east beach. The consultants say their statement is only true for the beaches to the west of the Port Royal beach. The storms of winter 2013-14 saw a lot of wave overtopping at the Port Royal beach because it is quite low on shingle and there is a harmonic effect on the waves between the western groyne and the eastern slipway.

2.      The consultants have calculated the average rates of erosion in eight Coastal  Behaviour Units along Sidmouth’s beaches. These calculations were made using data provided by Ordnance Survey and Plymouth Coastal Observatory. The consultants explained their methodology for measuring the cliff top and cliff base position over the years. Unfortunately, as pointed out by several members of the Steering Group, much of the data supplied to Halcrow had very large errors and distortion. In some instances the aerial photographs are grossly distorted resulting in measured positions of the cliffs that are absurd in that they are shown to be growing towards France by about 4.5 metres in 6 years. The consultants were asked whether they had gone back to the providers of the data to question about errors: they had not. They were also asked why they had included obviously erroneous data in calculating the average erosion rate: there was not really a satisfactory answer to this.

3.      One of the key Coastal Behaviour Units is CBU7. This extends from the river Sid 700 metres to the east. This is the CBU where there are very great errors in the input data. The consultants calculate an average erosion rate for a CBU by measuring the position of the cliffs at a number of points along the coastline in the CBU. CBU7 has markedly different rates of erosion around Pennington Point east of the river from the rest of the CBU further east. The consequences of the erosion around Pennington Point itself are much more severe than erosion further east. It seemed to me that averaging the erosion rate along the whole 700 metres was masking the real risks at Pennington Point and that the Point should be considered as a separate CBU. The consultants agreed that this approach was possible and it would be useful in considering options for the defence of that part of the coast.

4.      In assessing the damages from coastal flooding, the consultants have only included flooding due to wave overtopping along the town beach. They have not considered the effect of flooding due to wave overtopping once the waves are breaking directly against the west wall of the river (as will happen after about 5 more metres of erosion of Pennington Point). They said that this consideration was not within their brief. I pointed out to Councillor Moulding, the Chair, that this omission was not sensible since the damages were therefore being under-called. This would have an obvious impact on the justifiable funds for further defence works. I will be writing to Councillor Moulding to suggest that work should be done on this aspect.

5.      An engineer from Devon County Council showed pictures of possible positions for a replacement bridge across the river. Currently they are not looking further upstream than about halfway along the first leg of the footpath on Salcombe Hill for the eastern footing. This is because they are trying to re-use a bridge that they have in stock, which is that length. At that position it will not be economic to install the bridge unless coastal erosion at Pennington Point is significantly reduced within the next few years. I think it is likely that they will have to look at a bridge with the eastern footing further up the path at the bend. In the meantime, DCC will be monitoring the erosion at Pennington Point themselves in order to judge when the temporary bridge becomes unsafe.

6.      An engineer from South West Water described the facilities at the Ham and explained that most of the control functions are housed behind the western river wall just upstream of the current Alma Bridge piers. There are east-facing ventilators along this wall into the control rooms. These facilities will come under threat once the sea waves are breaking against the river wall. He also explained that the river training wall, which extends out to sea, also gives some protection to the sewer outfall pipe. If there is a proposal to remove the river training wall, then SWW would have to review the threat to this pipe.

7.      An Environment Agency representative then gave a quick overview of the process for applying for funding for further defence work. He said that work on the river defences could not be undertaken with funds that were justified by front coastal flooding alone. The justification would have to consider both river and coastal flood threats.

8.      The current plan for the BMP project is for a long list of beach management options to be prepared for comment by November 2015. These will then be revised into a shortlist for consideration by the Steering Group in February 2016 and the project should be completed by May 2016. The recommendations can then be submitted to the Environment Agency/DEFRA to request funding for further beach management works. The Environment Agency then said that the earliest funds could be available for use would be 2018 but see comment 7 above, since more investigation work may yet be required.

See also:
Futures Forum: 23rd July 2009: "DCC supports the ‘hold the line’ policy option for continued investment in maintaining existing coastal defences to prevent flooding and erosion, and to leave undeveloped and open coast to evolve naturally."

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