Author(s): Steven F. Daly
Linked Author(s): Steven F. Daly
Keywords: No keywords
Abstract: It is well known that wide river ice jams can become grounded, especially near the downstream end, or toe, of the jam. The geometry of wide rivers jams has been successfully modeled by solving an ice jam force balance equation assuming that the ice floes comprising the jam act as a granular material. However, to date, the grounded portions of wide river jams have been explicitly excluded from the ice jam models. This exclusion means that stresses acting through the ice in the toe region and flow through the grounded portion are both neglected. This neglect comes with a price: ad hoc assumptions regarding the source of jam stability in the toe, as well as “non-intuitive” and confusing numerical strategies to prevent the ice from contacting the bed during solution of the ice jam force balance equation. In this presentation the obstacles to modeling grounded portions of ice jams are addressed. The fundamental obstacle is that the vertical stress distribution employed by current models explicitly requires that the ice float at hydrostatic equilibrium, a condition not found in grounded portions of jams. A generalized vertical stress distribution is presented that covers the possible range ice submergence. Water flow through the grounded portion is modeled assuming high Reynolds number porous flow and using flow parameters based on field and laboratory observations. The ice jam force balance is modified to include the generalized vertical stress distribution and the resistance of the bed and the drag of the flow through the grounded portion. The one-dimensional steady flow equation is modified to include flow through the jam as well as under-jam flow and open water. The force equation is then closely coupled with the flow equation and the two are alternately solved to arrive at the final stable ice jam geometry. Procedures for dealing with irregular cross sections in the grounded portions and other practical difficulties are suggested.
Year: 2008