We begin a study of the dynamics of ice motion during river breakup by formulating a kinematic model. Ice continuity equations are applied to relate the speeds of a breaking front, a convergence front, a stoppage front, and a release front with the ice discharge and volume per unit surface area (unit volume) on either side of each front. Ice velocity was measured with time during a dynamic breakup at a pair of sites bounding a reach of the Connecticut River. We simulate the ice and front motion through time for this reach using the kinematic model with the assumptions that accumulation thickness and porosity are uniform, and that changes in the ice conditions and motion occur only at a front. Contrary to the basic assumption of static jam formation, we find that the accumulation developed while the ice was moving, and that jam formation merely represents the arrest of the motion.

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