Ice Cover Effects on Scour in Narrow Rivers (Ice Engineering, April 2005)

• Main Authors: Zabilansky, Leonard J., White, Kathleen D.
• Other Authors: ENGINEERING RESEARCH AND DEVELOPMENT CENTER HANOVER NH COLD REGIONS RESEARCH AND ENGINEERING LAB
• Format: Text
• Language: English
• Published: 2005
• Subjects: Hydrology; Limnology and Potamology; Snow; Ice and Permafrost; Civil Engineering; *ICE FORMATION; *PIERS; *RIVERS; *OPEN WATER; VELOCITY; LABORATORY TESTS; WINTER; ICE; LEVEL(QUANTITY); SEDIMENTS; FLOATING BODIES; FLUID FLOW; BRIDGES; CHANNELS; ROUGHNESS; GEOMETRY; HYDROSTATICS; SURFACE PROPERTIES; ENGINEERING; SEDIMENT TRANSPORT; INTERACTIONS; Ice; permafrost
• Online Access: http://www.dtic.mil/docs/citations/ADA442200; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA442200

The influence of an ice cover on a channel involves complex interactions among the ice cover, ice roughness, fluid flow, sediment, bed geometry, water depth, and channel geometry. This complex interaction can have a dramatic effect on sediment transport process (Fig. 1) and channel development, especially in narrow rivers. A river is considered narrow if the ice in the center of the channel is constrained from responding to changes in water level. In these situations, any increase in the discharge above the level at freeze up will necessarily be accompanied by an increase in the velocity under the ice cover. Recent laboratory investigations of scour around bridge piers explored three surface conditions: open water, a floating ice cover, and a restrained ice cover with hydrostatic head conditions simulating discharge increased above freeze up level. The study concluded that increases in hydrostatic head caused an increase in the maximum velocity beneath the ice cover for the restrained case and also found that the velocity profile is shifted towards the smoother boundary. This technical note summarizes the more detailed descriptions of the experiments contained in Hains (2004), Hains and Zabilansky (2004), and Hains et al. (2004). An ice cover approximately doubles the wetted perimeter of the river, adding to the flow resistance. When the ice cover becomes frozen to the riverbanks and bridge piers, the cover is restrained from freely responding to changes in discharge conditions. The ice cover forms at the stage corresponding to the freezeup discharge, defining the freeze up datum and subsequently the flow area for the remainder of the winter. Conveying a similar open-water discharge under a constrained ice cover requires an increase in stage, mean velocity, or both. The original document contains color images.