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|Title:||Morphology, hydraulics and sediment transport of an ice-covered river : field techniques and initial data|
|Authors:||Lawson, Daniel E.|
Chacho, Edward F.
Brockett, Bruce E.
Wuebben, James L.
Collins, Charles M.
Arcone, Steven A.
Delaney, Allan J.
Tanana River, Alaska
Cold weather conditions
|Publisher:||Cold Regions Research and Engineering Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||CRREL report ; 86-11.|
Abstract: This initial study of the ice-covered Tanana River, near Fairbanks, Alaska, attempted to I) establish field methods for systematic and repetitive quantitative analyses of an ice-covered river's regime, 2) evaluate the Instruments and equipment for sampling, and 3) obtain the initial data of a long-term study of ice cover effects on the morphology, hydraulics and sediment transport of a braided river. A methodology was established, and detailed measurements and samplings, including profiling by geophysical techniques, were conducted along cross sections of the river. A small, portable rotary drill rig equipped with a 356-mm (14-in.) ice auger was used to cut large diameter holes in the ice cover for through-the-ice measurements. Portable heat sources and a heated shelter were required to continuously thaw and dry equipment for the repetitive measurements. Measurements included ice cover thickness, water level, water depth, temperature, flow velocity, suspended load and bed load, frazil ice distribution and bed material composition. Remotely gathered data included apparent resistivity and subsurface radar profiling. The various techniques, sampling gear and problems encountered during use in the subfreezing cold are described in detail in this report. Preliminary results indicate that water flow below the ice cover occurs in distinct channels that are generally separated from each other by stagnant deposits of frazil ice. These deposits generally extend from the bottom of the ice cover to the river bed, acting as lateral channel walls for the sub-ice flow. Of the total area beneath the ice cover of each cross section, 35 to 50% consists of stagnant frazil ice deposits. Dimensions, hydraulic parameters and sediment transport rates vary among the sub-ice channels. A new form of frazil ice aggregate-called frazil ice pebble-is described. Its shape is reminiscent of water-worn stream pebbles with dimensions ranging up to 15 cm on the longest axis. Each frazil pebble consists of individual frazil ice particles or small aggregates of particles that are bound together by ice. They appear to develop from irregular aggregates of frazil that are eroded from frazil deposits and then transported downstream by the current. Their smooth and rounded form develops from bounding and rolling of the rough aggregates along the bottom of the ice cover during transport.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||CRREL Report|
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|CR-86-11.pdf||5.73 MB||Adobe PDF|