Winter overflow from ice gorging on shallow streams

Large quantities of frazil ice in shallow streams increase viscosity, decrease velocity, and increase the stage of the stream. High banks accommodate the increased stream state by allowing the rising frazil ice to form a bridge under which normal flow continues. Overflow occurs where stream banks are too low to contain the river stage. Low spots are filled with ice; the banks are built up with deposited slush ice, and a new river is formed. The ice-gorging and winter overflow of the Madison River was studied to ascertain whether the operations of the Hebgen and Madison reservoirs were responsible for the overflow in the 1916-17 season. An analysis of weather conditions for that period indicated that the overflow was caused by a sustained cold spell and not by reservoir operations. Photographs illustrate the ice blocked Madison River, overflowing farm lands. Ice forming factors are shown by graphs.