170 Sample issue The Journal of Pipeline Engineering Fig.2. General layout of the Nord Stream pipeline’s German landfall.
3rd Quarter, 2009 171 barrier of ships, known as ‘Schiffssperre’, is a designated historic monument. One of the shipwrecks, identified simply as No 67, has recently been successfully recovered from the sea bed and placed in wet storage to allow access for the laybarge and dredging vessels. The unusual S-shape of the route within the Greifswalder Bodden has been designed so that the pipelines can be installed within a defined planning corridor designated as a marine priority area within the planning policy of the regional development of Mecklenburg-Western Pomerania. The environmental and ecological restrictions within the protected areas have essentially determined the construction schedule and have had such a significant and direct effect on the project’s technical aspects that numerous installation methods have had to be designed, proposed, modified, and ultimately accepted to minimize the environmental impact and maintain the construction operations within the available time period. Onshore, several environmental-mitigation measures will have to be undertaken prior to the start of construction at Lubmin. These include the construction of habitats for lizards, amphibian pathways, solid partition fencing/ screening, and transplantation of small trees and bushes. Additional permit restrictions, including dredging and cofferdam installations, are not allowed to commence before 15 May, 2010, due to the herring-spawning season in the Greifswalder Bodden, and all offshore construction work must be completed in one construction season, i.e. by 31 December, 2010, within the FFH areas in the area of the German landfall. Noise-restriction guidelines have been set, at the nearest residential towns adjacent to the pipeline route, where the levels shall not exceed 50dB(A) during the daytime and 35dB(A) at night-time; additionally noise levels at the adjacent marina shall be monitored and shall not exceed 65dB(A) during the daytime and 50dB(A) during nighttime. Geological formation The offshore area crossed by the Nord Stream pipeline within the German sector can be divided into four different geological sectors: the Greifswalder Bodden, the Boddenrandschwelle, the Oder subsea valley, and the Oder Bank. Each area was formed by the glacial processes in the last ice age and the subsequent marine progression of the Baltic Sea and can generally be distinguished by their different water depths. The Greifswalder Bodden is almost a land-enclosed basin with a water depth up to 10m. The seabed of this basin is characterized by the variation of a large number of soil types, such as sand and gravel, peat, clay, or alluvial mud, which is typical for lagoon-like areas. At its eastern edge the basin is restricted towards the Baltic Sea by a submarine barrier with water depth of less than 5m. This barrier is called the Boddenrandschwelle, and is formed of glacial till (a cohesive mixture of clay, sand, and gravel) with loose residual sediments (sand, gravel, cobbles) generally at the uppermost (surface) layers. The Oder valley formation, an ancient course of the river Oder during the end of the last ice age, runs parallel to the Boddenrandschwelle. The water depth in this subsea valley ranges to 20m and above. The sea bottom is composed of coarse-grained fluvial sediments which have been covered by recent alluvial mud deposits. The major part of the pipeline route within the German sector crosses the Pomeranian Bay east of the Oder valley along the northern foothill of the Oder Bank. The sea bottom is characterized by marine sediments (largely sand), with water depths varying from 15m to more than 20m. German landfall At the German landfall the Nord Stream pipeline is divided into three separate sections: the offshore section, the ‘pullin’ section, and the dry section. The German landfall offshore section commences approximately 1km seaward of the highly-protected Greifswalder Boddenrandschwelle and Parts of the Pomeranian Bight (DE 1749-302) FFH-area, and extends in a south-westerly direction for 26km to approximately 1,100m from the shoreline at Lubmin. The pull-in section then commences and ends approximately 220m landward of the shoreline. The remaining 300m consists of the dry section up to the pig receivers. Sample issue Dry section The dry section generally comprises an ‘Omega’-shaped spool arrangement and a combination of valves (emergency shutdown and gate) together with isolation joints and pig receivers. The 48-in pipework is connected to the Greifswald receiving terminal (GRT) by way of twin 38-in diameter pipelines and supplementary 16-in by-pass lines. The dry section works were originally designed with a ‘dogleg’ arrangement; however, subsequent to a periodic environmental survey, it was discovered that the Grey Dune vegetation had migrated onto the pipeline route, thereby necessitating a realignment of the pipeline route and a redesign of the onshore pipework The dry-section pipework and permanent-work items will be supported by over 100 reinforced concrete bases of varying sizes.
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