Suspended sediment concentration and deformation of riverbed in a frazil jammed reach

Abstract

The presence of ice in rivers affects hydrodynamic conditions through changes in both the river's boundary conditions and its thermal regime. Therefore, the characteristics of sediment transport and the deformation of the river channel in ice-covered rivers are quite different from those experiencing conventional open channel flow. The variables of ice behavior, ice jamming extent, sediment transport, and deformation of the riverbed during ice periods are interrelated on the basis of both physical arguments and field experiments of river ice jams in the Hequ Reach of the Yellow River. The characteristics of sediment concentration in water, frazil ice, and ice cover are described. Analyses have been made on the mechanism of the evolution of frazil jam and the associated adjustments in the riverbed. It has been found that the evolution of the ice jam and the deformation of the riverbed reinforce each other. The interrelationship between the particular features of evolution of ice jam and deformation of riverbed is summarized here in the form of regression relationships relating the hydraulic parameters of water under ice jams to the deformation-extent of the riverbed and the jamming-extent.Key words: deformation of riverbed, evolution of frazil jam, frazil jam, suspended load, sediment concentration.

Sediment Transport under Ice Conditions

“…This section examines sediment transport and riverbed deformation in the Hequ Reach of the Yellow River in China, as outlined by Sui et al (2000Sui et al ( , 2006. The Hequ Reach of the Yellow River is approximately 700 kilometres in length and has a broad and shallow morphology.…”

“…The largest recorded sediment concentration in frazil ice in the Hequ Reach was 25 kilograms per metre cubed of ice; this is a much larger sediment concentration than what has been recorded in water flowing under the ice (7 kilograms per cubic metre of water). During an ice jam event from December 1986 to March 1987 Sui et al (2000) examined riverbed deformation at a cross section in the Hequ Reach. As shown in Figure 6, over the period of approximately 3 months, the river width expanded and sediment scour expanded the deepest parts of the river channel.…”

“…Any frazil ice will be transported to the ice jam toe and deposited. Based upon extensive field observations of ice jam formation and frazil ice transport, Sui et al, (2000) proposed that frazil ice formation and riverbed deformation reinforce each other. The authors found: a. as an ice jam grows, the riverbed will be scoured.…”

Numerical simulations of ice accumulation under ice cover along a river bend

“…Starosolszky (1970) and Sui et al (2000) suggested that the theory of bed load movement could be borrowed to describe the movement of ice under ice cover. Atkinson and Waters (1978) used Meyer-Peter formula to describe the movement of ice particles.…”

“…An ice cover alters the hydraulics of an open channel by imposing an extra boundary to the flow, altering the water level and flow velocity compared to the ice free case . Ice alters the flow regime, incipient motion of bed material and the transport of sediment by temporarily storing water through ice jams and results in differences in riverbed deformation as compared to that observed under open flow conditions Sui et al, 2000;. Under specific conditions such as continuous incoming of frazil ice from upstream due to low temperature, ice jam may be formed.…”