Seasonal and Long-Term Within-Channel Permafrost and Its Effect on Northern River Navigation

Frozen ground within river channels is widely observed on most Russian Arctic rivers with sand-clay alluvium. Within-channel permafrost determines high long-term stability and site-specific trends in channel development, affecting northern rivers navigation conditions. Extensive field studies on 200-km reach of Lena River in Central Yakutia, largest in the region, show that navigation conditions are majorly impaired by permafrost-affected narrowing, increasing length and curvature of fairways. Economical effects of such impairment, including gross operational costs, dredging operation and new fairways development expenses, were estimated based on statistic data provided by Lena Basin State Waterways & Navigation Authority. Average additional gross operating costs (per 1 km of fairway length) were estimated about US $60 to $100 per ship passage, including ship maintenance costs, fuel and crew expenses. Furthermore, above 1.5 M m³ of bed material were excavated within the studied reach during years 2003-2007 to maintain safe ship operations, adding another us $6 M to the total expenses. Study results reveal, that permafrost and related channel dynamics add to the northern navigation costs. Facilitation of the latter includes forecasts of permafrost-induced channel alterations. A probabilistic model using hydrological data was developed in order to assess the spatial extent of within-channel permafrost and its potential impact on channel dynamics. Modeling results for the studied 200-km Lena river reach appear to be consistent with field observations, thus allowing introduction of the model in forecasting and decision-making processes during waterway development planning.