Temperature variations and heat flow in coastal soils in the Arctic. Monitoring and modeling the thermic state of soils surrounding the landfall pipeline of Longyearbyen, NO

Offshore development on the Arctic shelf requires the construction of pipelines providing the transport of hydrocarbons from the shelf on shore. The infrastructure development assumes also the construction and support of pipe-lines crossing water barriers (bays, rivers, lakes). Erosion and ice processes in the coastal zone can influence conditions of the pipeline laying in the coastal zone and representing a possible cause of accidents. Temperature control is necessary to maintain the fluid in the pipeline at the necessary flowing temperature and to prevent excessive warming of the surrounding soil with consequent permafrost thawing. When pipelines cross the shore they represent a challenge for pipeline management as they are at the border between onshore and offshore conditions. This study represent the continue of the research project started in 2011and ended in 2013 with the aim of analyzing the thermic state of shore soils surrounding the Longyearbyen power plant landfall pipeline and creating a numerical model to simulate temperature variations in soils. Particular attention was put in investigating how the tide cycle influences the heat transfer in the soils. Soil temperature data were used to calculate horizontal and vertical heat fluxes inside the shore soils. Soil temperature and heat fluxes series were put in relation with pore pressure measures to see how oscillations of the underground water level, caused by tide cycles, is affecting temperature and heat transfer variations. Four numerical models were developed with increasing complexity to simulate two years of temperature changings in soils. Comparisons among models were useful in understanding how atmospheric temperature, pipeline temperature and tide cycles concur in defining the temperature field of shore soils. Models showed, in accordance to field evidences, that tide cycles are responsible of short term, see semidiurnal or diurnal, since weather condition can’t affect so quickly soil temperature especially during winter. Tide cycles increase the absolute value of vertical heat flux between deeper soils and ground surface.