Possibilities of ice jams forecasting using river channel computer models

Possibilities of mathematical modelling of ice cover breakupand ice jams in the rivers of Siberia are considered. By example of the Tom River the technique for forecasting ice jams on the basisof calculation of ice cover break-up with the use of one-dimensional computer model НЕС-RAS is developed. With sufficient informationon the river channel geometry and hydraulic characteristics of the stream in representative cross sections the model allows predictinga set of parameters of the stream in a lengthy channel, including the presence of ice cover and ice jams with sufficient accuracy. Theassumption of existence of dependence between the possibility of ice jam and certain combinations of characteristics of stream energyand ice cover thickness is put forward. The formula for the factor of ice cover break-up, depending on the kinetic energy of the streamand ice firmness, is offered. The model of 23 km of the Tom river channel near the city of Tomsk and upstream is developed and calibrated.The analysis of the break up factor change for the maximal and minimal ice firmness and various water discharges, which characterizekinetic energy of the stream, has been implemented. The sites of ice cover break-up corresponding to the reaches with highkinetic energy of the stream, and the sites of ice jams formation where kinetic energy decreases to the critical value are graphically determined.It corresponds to the long-term field observations data. Also an opportunity appears to define the quantity of ice in the body ofjam, which has come from upstream and which depends on the length of the reach where the break-up occurs, ice thickness and channelwidth. Depending on channel morphology and quantity of ice in a jam it is possible to predict places of complete damming of the riverand a danger of significant water level rise with flooding neighbouring territories. The analysis has been implemented and possible icecover break-up scenarios for the Tom River within the city of Tomsk for extreme (minimal and maximal) values of ice firmness andhigh water discharges have been offered.

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