Evaluating the impact of fluvial geomorphology on river ice cover formation based on a global sensitivity analysis of a river ice model

Abstract

In 2011, Manitoba was stricken by wide-scale flooding causing high flows along the Dauphin River. The unprecedented high discharges at freeze-up created the potential for excessive ice cover thickening and backwater staging exacerbating the flood risk already threatening the communities along the river and upstream-lying Lake St. Martin. Hence, the river ice model RIVICE was implemented to determine flood protection elevations to which existing dikes needed to be raised and extended. Two reaches of the river were modelled separately representing distinct geomorphological characteristics: mildly sloping, more sinuous upper reach and steeper, more channelized lower reach. A global sensitivity analysis based on a Monte Carlo analysis was carried out to determine how differences in these morphological features influence different processes of the ice cover formation. It was found that the sinuous and braided morphology of the upper reach has a marked impact on the sensitivity of the hydraulic roughness and strength parameters. The structure of the ice (porosity) and the discharge were most sensitive to the backwater level outcomes of the steeper and straighter lower reach.