Desk review of coastal evolution studies at UKAEA Dounreay
Auton, C.A.; Pearson, S.G.; Hobbs, P.R.N.. 2007 Desk review of coastal evolution studies at UKAEA Dounreay. Nottingham, UK, British Geological Survey, 30pp. (OR/07/017) (Unpublished)Before downloading, please read NORA policies.
This desk review evaluates existing studies relating to the evolution of the coast adjacent to the Dounreay nuclear site and assesses their relevance to determining rates of past and future coastal change on the shoreline seaward of the proposed new Low Level Waste Facilities site. It considers the robustness of the existing UKAEA approach, identifies key areas of uncertainty and possible methods for reducing them, and proposes new methods of coastal erosion monitoring that can span the 30 year time frame for low level waste disposal in the new facilities. The review considered data, results and interpretations of coastal erosion rates for the Dounreay Shaft and Low Level Waste Pits areas, produced between 1995 and 2001. These were presented in five reports and one published paper. The studies used innovative techniques to assess both the erosive processes active on the cliffs and foreshore and to provide numerical estimates and models of annual rates of coastal retreat. These were systematically treated to provide the best evaluations that were possible at the time, but more modern methods are now available that should enable more realistic estimates of erosion rates to be made. The quality and detail of the data gathered during these studies increased in successive reports. They provide comprehensive literature reviews, summaries of the geology and geomorphology, and forecasts of future coastal erosion rates. Future shoreline and cliff top positions are shown in plan and cross-section. The data is illustrated on annotated aerial photograph mosaics, cross sections and simple coloured plans and maps. Computer-generated cliff-shoreline profiles, graphs of calculated rates of cliff recession, and rockhead contour plots were also produced. However, recommendations for further work were not implemented. Identification of the principal erosive processes active on the coast were thorough and the conceptual modelling of their effects incisive. The influence of effects of present climate and predominant wave direction were recognised and attempts were made to evaluate the effects of past and future climate and sea-level change. These latter estimates have become somewhat out-dated by the growing and ever changing estimates of future sea-level change and the extent and age of past glaciations. The reports provided estimates of maximum rates postulated from the Shaft and LLWP areas under 3 scenarios. Their possible impact on the new LLWF on time scales of 10,000 to 25,000 years rates is summarised in the report by Morgan and Wilmot as: Scenario – 1 ‘Normal Evolution’~ 2m sea-level rise = erosion concentrated in geos; Scenario 2 -‘Extended Global Warming’ ~5m sea-level rise = erosion of 55mm pa (550m in 10ka);Scenario 3 - ‘Ice sheet collapse ~ 9.5m sea-level rise = erosion of 55mm pa for first 5ka, 30mm pa for the next 20ka (875m in 25ka). A more conservative rate of 10mm pa was subsequently adopted for the coastal constraint on the location of the new LLWF site. Many of the key uncertainties identified relate to limitations of the techniques available at the time of the studies. These include positional accuracy of some early measurement positions, the ability to scale-up limited 2 dimensional measurements to site-wide estimates, the difficulties of dating of erosional features and the somewhat simplified understanding of the geological complexity and variation within each site. The geological framework of the Dounreay area is now much better understood, largely due to subsequent and on-going site investigations. The problems of 2D modelling and measurement can now be largely overcome by recent advances in GIS and 3D computer modelling packages and modern field surveying equipment, such as dGPS and Laser scanning. Consequently, a more rigorous approach to monitoring bulk rates of coastal erosion in three dimensional space is possible and, with sequential monitoring over a 30 year period, a more complete four dimensional model of past and future coastal change is possible. The problem that short-term observations of erosion rates may not be truly indicative of long-term rates, and the possibility that no conclusive change in cliff position occurs during the 30 year operational life of the LLWF still exists. However, the use of lichenometry to date portions of the cliff line and rock platform, offers the opportunity to establish zones where negligible erosion has occurred during the last several hundred years. Sequential (every 5 years) targeted laser scanning of cliffs, slots, notches and foreshore platforms, from characteristic coastal zones (determined by an initial photogrametric survey), allows highly accurate quantitative measurement of both vertical and lateral erosion by a single technique. This, together with programmes of erosion pin monitoring, on-site and laboratory geotechnical testing, targeted to cover the range of rock types known to be present across each scanning site, will give objective geo-referenced measurements. These will enable 3D erosion rate monitoring and also the construction of 4 D bulk rock mass assessment models of coastal evolution that accurately reflect changes during the 30 year monitoring period. The techniques will also produce numerical data suitable for inclusion in time-series computer models of future coastal evolution of the site.
|Item Type:||Report (UNSPECIFIED)|
|Programmes:||BGS Programmes > Geology and Landscape Northern|
|Additional Information:||Contributors: T Bradwell and J D Everest|
|Additional Keywords:||Coastal erosion, Caithness, Highland Region, Northeast Scotland|
|NORA Subject Terms:||Earth Sciences|
|Date made live:||26 Jun 2009 14:17|
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