The Blue Stream pipeline project is a gas transportation system for the delivery of processed gas from a gas station in the southern Russia across the Black Sea to Ankara, Turkey. The Turkish landfall of the offshore pipeline in the Black Sea is located near Samsun, see Figure 1 for the pipeline route. One of the main aspects of the design of pipeline through a morphologically dynamic area such as landfall is the required burial depth (Chen et al, 1998, 2001 and Bijker et al 1995). The burial depth is the result of an optimisation between: • safety of the pipeline (which often requires a large burial depth), and • environmental impact and trenching costs (a small burial depth means less dredging and less environmental impact). This paper presents a method of predicting the future extremely low seabed level in a morphologically dynamic landfall area, which is required to determine the burial depth of the pipeline. Both short term and long term coast evolution were assessed to quantify the expected lowest seabed level along the pipeline route in the landfall area during the pipeline lifetime of 50 years. The results were used to determine the required pipeline burial depth. The long term morphological changes originate from long term variations in the morphological system (e.g. river input), gradient in the longshore sediment transport and long term variations in the hydrodynamic conditions. The short-term morphological changes originate from beach profile variations due to cross-shore sediment transport as a result of seasonal and yearly variations in the wave and current conditions. Numerical modelling was applied to compute the longshore and cross-shore sediment transport rates and the resulting coastline evolution and cross-shore profile evolution. The longshore transport model was validated using the available data on the coastline changes in the past 20 years, which was derived from the satellite images. The 50-year lowest seabed level has been determined as the sum of the coastline retreat and the cross-shore evolution in the next 50 years.

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