Modeling the Release of River Ice Jams and their Impact on River Bed Scouring.

Abstract

The Great Lakes are the largest fresh water reservoir on the planet. Lakes Huron and Michigan drain into Lake Erie through the Huron Erie Corridor. The average water level in Lake Huron has been dropping. The results of hydrodynamic model simulations imply that there has been an increase in the conveyance of St. Clair River that took place in the 1980’s. 1984 was marked by a massive ice jam. The jam had a duration of 24 days and its release was accompanied by high flow velocities. It is speculated that the high water flow velocities following the release of the jam caused scouring of the river bed, that lead to an increase in conveyance. A model is developed to simulate changing river bed morphology, and is combined with a hydrodynamic model in order to simulate scouring during the release of an ice jam. The model consists of modeling the river bed morphology, finding the sediment fluxes on the bed, and updating the bed morphology when scouring occurs. The hydrodynamic model uses a step-wise approximation for the bed morphology. A geometric scheme is developed to compute the local angle of inclination. The bed elevation is updated by numerically solving the Exner equation by using a finite volume approach. A new methodology is developed in order to adapt the grid to the changing bed morphology.

The ice jam is modeled as an initially stationary body of water. Water is allowed to flow freely under the body. The body of water is released in the flow, accelerating and causing flow velocities over the entire river to rise rapidly. It is found that an ice jam similar to the 1984 ice jam will cause scouring of the river bed.