The following brief of evidence was given by Professor Andrew Cooper at the second Bord Pleanala Oral Hearing on 30 March 2007 on behalf of the Greystones Protection and Development Association.
1. Qualifications and Experience
I graduated in 1984 from Queen’s University Belfast in geology, and I was initially employed in southern Scotland on a geological reconnaissance project with BP Minerals. I moved to South Africa in 1985 where I worked for two years in the University of Natal on sedimentation in estuaries and a further seven in the CSIR on coastal processes. I gained my MSc and PhD from the University of Natal in 1987 and 1991, respectively. I took up a senior lectureship at the University of Greenwich, UK in 1993 and a Readership at the University of Ulster in 1994. I was appointed to a personal chair in coastal studies in 2004. I have published more than 200 papers in the field of coastal processes and coastal management and have worked on a variety of research projects in the UK, Ireland, the EU and around the world.
2. Introduction
My evidence today is on behalf of the Greystones Protection and Development Association, and arises from the Association’s concern about the applicant’s proposal for beach nourishment to mitigate the impacts of its proposed marina development at Greystones Harbour.
In my evidence I will address the question of the mechanism of delivery of beach recharge material to the site, the volume thereof and the long term implications of this approach.
My evidence will have particular regard to the question raised by the Board in its letter dated 14 August 2006 to Wicklow County Council. In that letter, the Board stated
“Noting the already restricted road access to the site, the Board is not satisfied on the basis of the submissions made that the required beach nourishment of approximately 6,000 tonnes per annum cannot be brought to site by sea in order to mitigate any potential negative traffic impacts resulting from the proposal to bring this material by road, and consequently through the future completed development”.
3. The Applicant’s Proposal for Beach Nourishment
The applicant considers, on the basis of numerical modelling of coastal processes, that accelerated coastal erosion is likely to result from the proposed development. It has been proposed that this be addressed by rock armouring of the seaward edge of the old dump site and beach nourishment in the area north of this for a period of 30 years. The recharge material is to be sourced from gravel quarries on land and transported by lorry to the beach at a rate of 6000 m3 per year, following an initial emplacement of 30,000 m3. Calculation of these required sediment volumes relies on future predictions of shoreline behaviour under various scenarios. Because the volume of material being transported to the beach is the subject of the board’s letter of August 14th to the developer, I would therefore like to look briefly at the means by which these required volumes are derived.
3.1. Beach behaviour: actual and predicted
Beaches are loose accumulations of sand and/or gravel that can adapt their shape to variations in wave, tide and wind conditions, sediment supply (volume of available material) and sediment type (size, shape and composition). They do so within a fixed geological framework. They may be bounded by headlands or underlain or backed by rock of variable resistance to erosion. The beach adjusts to the combined effect of these parameters at any given time and hence achieves a dynamic equilibrium. A change in any one of these factors may produce a change in the beach itself.
Construction of the marina changes the framework within which the beach exists. This changes the physical boundaries within which the beach exists, which in turn alters the wave dynamics. This adjustment in two of the major controls on beach shape and position will produce a change in the beach shape. There is no accurate way of modelling the likely future shape of the beach under such conditions .
The models (part of the DHI Litpack suite) that were used by the applicant (Greystones Harbour EIS Appendix 6) to predict shoreline evolution for different marina scenarios are complex numerical models that aim to make various predictions regarding, coastal hydraulics, volumes of longshore sediment transport, and future shoreline positions under various scenarios. In order to make accurate predictions of future shoreline positions and sediment transport rates, such models must take account of all the variables that impact on sediment transport .
There are several reasons, however, that mean that such models cannot produce accurate simulations. They include the following:
Certain important parameters to be omitted from calculations (e.g. packing and density of sediment);
Not all important model parameters and their interactions are understood. Scientific understanding of transport of mixed grain populations is very limited ;
There is a ubiquitous inability to accurately characterise the starting conditions (grain size, wave conditions, precise beach shape, underlying rock depth, resistance to erosion etc); For example, the Greystones beach is described in the developer’s reply to the board’s leter of August 14th 2006, simply as “shingle with a median size of 5mm”. This gives no indication of the range and proportions of grain sizes and shapes.
Some questionable relationships are used in models (e.g. relationship between wave angle and longshore drift rate);
Constants are frequently used to adjust model outputs to achieve ‘reasonable’ predictions. For example, a range of wave theories can be selected as well as bed roughness parameters and wind or currents can be omitted or included as the operator chooses- this enables the operator to adjust the model result to match a target value;
The unpredictability of future wave, tide and weather conditions.
The role of extreme but infrequent storms, that may strongly influence or even dominate shoreline behaviour cannot be predicted or simulated. These may produce much more change in a few days than decades of ‘normal conditions’. At Kilpatrick beach in northern Wexford, for example, storms in early December 2006 caused more than 10m of erosion on a beach and dune that had been essentially stable for the previous decade;
Using the models produces a single quantitative prediction without giving any indication of the probability of such a scenario actually occurring. One can have little confidence in such a simulation and in the case of Greystones, the predicted impact of the marina derived by modelling is therefore quite uncertain. As a consequence, the volume of material required to ‘remedy’ the situation cannot not known. The volumes cited (6000m3 per year and an initial capital emplacement of 30,000 m3 may be much too low or much too high. Raising the amount from 4000m3 to 6000m3 as has been done in the EIS to ‘ account for the inaccuracy of the 1-D model) has no basis in reality, as the model has no error bands.
3.2. Required volume of nourished sand
The practice of placing sediment on an eroding beach to replace or augment natural sediment supply is now widespread practice in many heavily developed coastal areas. Because of the complexity of interactions outlined above, it is not possible to accurately predict future beach nourishment requirements or longevity of nourished beaches. Models are commonly used to make such predictions but they suffer from several fatal shortcomings.
The inability to predict performance of beaches using models relates to several factors. One is the inability to describe the grain size; Beaches contain a range of different grain sizes distributed throughout the beach). Another is the inability to describe the wave conditions; Natural seas are affected by a range of wave sizes that interact with each other, with the wind and with any currents to produce complex fluid motions that vary over time. The role of storms is particularly poorly understood. A third is the chaotic behaviour of the weather that produces waves and currents.
Studies have shown that nourished beaches almost always last for a shorter time than that predicted. Usually, the poor performance is explained by an unexpected storm and there have been several instances when entire nourished beaches have been eroded within a few days. The inaccuracy of models is certainly a contributing factor to poor performance, but the overwhelming dominance of over-predicting the longevity of nourished beaches shows an ill-placed optimism in many such exercises.
The potential situation whereby nourished material is washed away rapidly by a storm is not considered in the developer’s report.
As a result of sea level rise and climate change resulting in the likely increased incidence of storms in the Irish Sea, the volume of material required to maintain the beach position will not remain constant but an ever greater volume of material will be required in the future. There is no commitment to providing a greater volume than that laid out in the developer’s proposal. Furthermore, any increase in volume would increase the traffic volume and level of disturbance on the beach.
3.3. Suitability of proposed fill material
The beach at Greystones derives its sediment from the eroding cliffs of fluvio-glacial sediment at the rear of the beach. This material has been initially sorted by ancient, glacial-related processes and when it is eroded by modern waves it undergoes further sorting on the beach. This produces a distinctive distribution of sediment according to grain size and shape on the beach. A particular packing arrangement is achieved whereby the grains fit together in a particular way. Using material from a different source (an inland quarry) and depositing it directly on the beach by a different mechanism (dumping from a lorry) produces a different packing arrangement and will cause the beach to respond differently to wave processes. Nourished beaches are usually found to erode more rapidly than their natural predecessors.
In addition, no quantitative analysis of the textural characteristics of the proposed source material and the natural beach source material has been undertaken to determine the differences. The high incidence of broken stones in the Ballyhorsey quarry material and its angular nature contrasts markedly with the smoothed and rounded nature of the present beach material. The possibility of use of offshore marine sediments is considered in the developer’s reply but is subject to many uncertainities. The land-sourcing and transport of nourishment material seems to be favoured.
3.4. Environmental value of nourished beach
Beach nourishment involves a high level of vehicular and mechanical activity around and on the beach. This disturbance will have adverse impacts on plant and animal life on the beach. Upper beach vegetation will be disturbed by the movement of imported material across and on the beach. The beach infauna will be buried and the different styles of packing and probability of fine interstitial grains may affect biological colonisation and use of the beach surface. It is unlikely to be packed and sorted by mechanical emplacement in the same way as it would be by waves and this may impact on the recreational value of the beach.
3.5. Sustainability of nourished beach
Above all, it is important to note that the beach nourishment is being proposed as an antidote to problems that will arise through construction of the proposed marina. It is an acknowledgement that an undesirable impact will be created and is a proposed mechanism to reduce this impact. The nourishment is proposed to continue to be financed and undertaken for thirty years by the marina operating company. At the end of thirty years, however, when the nourishment stops, the adverse impacts of the marina will still remain. The resulting problem or accelerated erosion, even if the nourishment performs as the developers expect, is therefore not mitigated but simply forestalled or postponed. The question of who will take responsibility for the adverse impacts on the coast at that time remains unresolved. It would seem unreasonable for the public to take over such responsibility since the impact is the result of private development. If not, how would the adverse impacts be managed at that time?
Once humans interfere with a shoreline, there is usually no going back. The first intervention typically produces undesirable impacts which require additional interventions to ’remedy’ them. They in turn produce further impacts and the beach is transformed from a natural system to an increasingly human-influenced system, dependant on political decisions and economics for its survival. The artificially nourished beaches of southern Spain, backed by sea walls and defended by offshore breakwaters are ultimate expression of this urbanisation of beaches. There, the high volume of beach-dependant tourism activity provides an economic driver to sustain beach nourishment. No such driver exists at Greystones.
Nourishing a beach creates an artificial condition and a commitment to sustain that beach for ever. This is a major commitment for this and future generations to enter into, in order to resist changes that are the result of a one-off marina development.
4. Conclusions
On behalf of the Greystones Protection and Development Association we suggest to An Bord Pleanála that this development will have unpredictable and unquantifiable impacts on a natural beach system. The proposed mitigation by beach nourishment will have negative impacts on the natural environment and the local infrastructure. The volume of material required to maintain a given beach position cannot be known and any increase in volume required would have additional environmental impacts. Most importantly, the practice is not sustainable. The development will create a permanent environmental problem that will persist (and most probably be excerbated) beyond the thirty year lifespan of the proposed interventions.
Andrew Cooper
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment