Self-organizing water rise process preceding river ice-jams

Abstract

Distributions of daily average water levels prior to ice-jams and in jam-free periods during spring breakups in the Lena river were constructed. The results showed that during periods of water rising in jam-free years, water levels were distributed in a random manner, in accordance with an exponential (Poisson-like) function. In contrast, water-level distributions during periods preceding ice-jams followed a power law similar to various multiscale hydrological phenomena, such as flood occurrences, return periods of rainfall, Arctic drifting-ice dynamics, and other nonequilibrium natural processes. However, the complexity of ice-jam floods is of a particular kind. In many cases, the power exponent in a water-level distribution (referred to as the b-value in a Gutenberg-Richter relation) increased sharply a few days before an ice-jam. In other words, a plot of the entire power-law distribution usually consists of two portions, differing in their slope. In terms of thermodynamics, an increase of the b-value leads to a decrease of the system conservation. To explain this effect, one should take into account that ice-jams are frequently preceded by advances of ice, which changes the energy balance in the water-ice system. As a result, the power exponent in water-level distributions appears to be higher in the partially fragmented ice cover.