Paper No. ICETECH06-120-RF Zaitsev 1 Spring Ice Processes on Rivers of North Eastern Russia A.A. Zaitsev Moscow State University, Faculty of Geography, Laboratory of Soil Erosion and Fluvial Processes Moscow, Russia zaitsev@river.geogr.msu.su V.V. Belikov 1 , N.I. Tananaev 2 1 Scientific Research Institute of Energy Structures 2 Moscow State University, Faculty of Geography, Laboratory of Soil Erosion and Fluvial Processes Moscow, Russia tananaevs@mail.ru ABSTRACT For short-term forecast of ice-jam levels, a model of river ice jamming, based on numerical solution of Sen-Venan equations using Militeev’s implicit scheme was developed. The model was enlarged with a simple model of ice-jam length increase. Computation of an observed ice jam was used for model verification. Computing velocity vectors on this model allows estimation of dynamic load on facilities within the river valley during flooding. Results of the research revealed the origin of extremely high ice-jam stages. High roughness factor of ice lower sur- face causes high stage rise upstream the jam. KEY WORDS: ice-jam modeling; flooding; dynamic load; ice dam. INTRODUCTION Investigations of spring ice processes on rivers include a large variety of questions concerning processes of both formation and failure of ice cover. Turbulent mixing and ice movement are the basic features of freezing and melting of river ice. Geographic location in specific way alters features of spring ice processes. Greatest rivers of North Eastern Russia (e.g., Lena, Yana, Indigirka, Kolyma) flow in direction from South to North, and it is the primary reason of specific ice processes’ appearance (especially ice-jamming). Ice jams are playing a significant role in formation and moving of spring tide wave on these rivers; its formation is caused by meteoro- logical conditions, river channel morphology, and partly by river valley morphology features, as ice jams appear at the same places annually. It is known that opening of these rivers begins in the southwards upper reaches, forming ice drift which is stopped in the middle and lower reaches, where ice cover is stable and quite thick (up to 1.5 – 2.0 m on the Lena river near Yakutsk). Ice drift stops, forming ice jams up to 50- 100 km long, causing stage rise up to 20 m. Flooding in Siberia affects mainly unpopulated areas; nevertheless in Yakutia nearly 90% of population and 75% of agricultural lands are situated within river valleys and can be exposed to flooding. Ice-jam caused stages’ rise repeat almost annually and lead to hazardous floods. Ice jams on rivers of European Russia are also dangerous; on the Sev- ernaya Dvina near Arkhangelsk ice jams are observed once every 4 years with maximum water rise up to 4 m. Extremely high water levels were also observed on the rivers Sukhona and Vychegda. Ice jams attract now much more attention, than even 15 years ago, due to growing material damage caused by them. Extremely high stages, recorded in recent years (1998 – 2001) on the Lena river, led to flood- ing of large flood-plain areas, damage of apartment buildings, port installations. On May 14-22, 2000 sudden stage rise due to ice jam caused floods on the Lena river reach from Lensk to Aldan’s mouth (nearly 800 km). Yakutsk city was fully inundated, with water level rising up to 100-yr recurrence. More than 169 settlements with popula- tion about 475 thousand people were inundated, 15 casualties. The flood of year 2001 was even more devastating. This was caused by active warming and snowmelt in the Lena headwaters, leading to ex- treme stage rise in the beginning of May, flooded Ust’-Kut and Kirensk (Irkutsk Region). Ice jam formed near Lensk, forcing stage to more than 17 m rise, exceeding observed maximum by more than 3 m. Two waves of ice-jam entirely flooded Lensk (43 000 people evacuated), 3 850 buildings destroyed with 1 casualty. Inundated area covered 10 districts of Sakha Republic, port installations of Ust’-Kut, Lensk, Olekminsk, Yakutsk were seriously damaged. General damage was estimated as 6 bln. roubles (~ $200 mln). Construction of flood-control dams and taking urgent actions to prevent or at least minimize flooding consequences require information on possible ice-jam high stages and flooded area forecasts. This paper outlines a method to calculate extreme stages and flooding areas, caused by ice jamming. Numerical solution of 1D and 2D Sen-Venan equations is used to model the processes of ice jam forming.