Numerical Modelling of River Ice in Complex River Systems
Creators: Blackburn, Julia L
Publisher: name: University of Alberta Library
Year: 2022

<p>Rivers in cold regions experience ice conditions for a significant part of the year.  River ice can cause ice jam flooding, impact hydropower generation operations, and affect a river’s ecological and morphological conditions.  Many ice processes are highly dynamic and are affected by meteorological / hydrodynamic conditions, and river geomorphology.  River ice can be very challenging to study due to the risks and costs associated with data collection in harsh winter conditions.  One of the most economical and efficient approaches to study river ice processes and to evaluate the effects of ice on a river’s regime is to use numerical model simulations.  At present, most existing one-dimensional (1D) river ice models are based on an implicit finite difference solution to the Saint-Venant equations.  As a result, highly dynamic events such as rapid ice jam formation or sudden ice jam release are difficult to model due to numerical instabilities that can arise if the flow approaches supercritical.  Also, river ice models with network modelling capabilities reduce conservation of mass and energy principles to continuity of discharge and equality of water levels at the junctions, which may not be reasonable when the ice and flow conditions are rapidly changing.  There is a need for a comprehensive 1D river ice process model that is capable of simulating the full ice regime in rivers with complex natural channel geometry where mixed flow regimes are anticipated.  The ultimate goal of this research is to develop a robust public-domain comprehensive 1D river ice process model, capable of handling complex natural channel geometry and channel networks for the full spectrum of scenarios from simple known steady ice conditions to highly dynamic cases such as ice jam formation or release.  In this study, a number of developments were made to the University of Alberta’s public-domain hydrodynamic and river ice process model, River1D, as steps towards realizing this ultimate long-term goal.<br>
Firstly, the model was reformulated to accommodate natural channel geometry and enhanced to include previously excluded ice processes.  Previous versions of the model allowed for a rectangular channel approximation only.  The new natural channel geometry version of the model was then enhanced to include new ice processes: water supercooling, frazil accretion, frazil re-entrainment, anchor ice formation and release, border ice formation, under-cover transport of frazil, and ice cover formation based on leading edge stability criteria.  The model was validated with freeze-up data from the Susitna River, Alaska.<br>
Secondly, the model was modified to simulate flow in channel networks using a momentum based approach to simulate junctions that includes important physical effects at junctions but without the need to adjust model parameters or redefine junctions should a flow reversal occur.  A series of steady and unsteady tests were used to assess this new approach.  The results were compared to and agreed favourably with results simulated with a two-dimensional (2D) model.  The unsteady test results demonstrated the model’s capability of handling transient flow reversals.  The model was then applied to a network of channels in the Mackenzie Delta for both open water and ice jam conditions.  Model results agreed well with observed water level data.  Modelled ice jam conditions indicated a flow reversal in the Peel Mackenzie Connector, which is consistent with observations in this channel during breakup.<br>
Lastly, the model was enhanced to simulate ice jam profiles in multi-channel networks.  The enhancements include provisions for handling junctions when solving the ice jam stability equation within a channel network.  The model was compared to a series of idealized test cases from a previous study that sought to investigate the impacts of islands on ice jam profiles.  Model results agreed very favourably with the results from the previous study.  The model was then applied to the Hay River Delta.  The model was validated for both open water and ice jam conditions.</p>