Author(s): Wojciech Majewski; Maria Baginska
Linked Author(s): Wojciech Majewski
Keywords: No Keywords
Abstract: Ice cover on open channels (rivers, impounding reservoirs) changes hydraulic conditions: flow resistance, velocity distribution and the relation between discharge and water depth. This may bring in many cases floods and inundation of large areas. Prediction of water stages is very important in engineering practice. It has to be based on real channel morphology, ice character and distribution as well as flow dynamics. The paper presents formulation of the mathematical model and calculation procedure for water surface profile (backwater) for steady, nonuniform flow with various ice cover. Morphology of river channel is given for the cross-sections in the form of depth and distance coordinates; roughness of the channel bed is represented by Manning roughness coefficient, ice cover is characterized by its thickness and roughness of its underside (Manning coefficient). These boundary conditions may vary in consecutive cross-sections and along river reach. Step method is applied -- calculations start from the initial (control) cross-section in which water elevation and discharge are given. Conveyance principle is applied and overall flow resistance is represented by composite roughness coefficient which takes into account bottom and ice roughness. Various ice cover conditions are taken into account: continuous ice cover, hanging dams, border ice, ice jams extending over certain river reach and ice free channel formed by icebreakers. Examples of calculated water surface profiles with ice cover are presented for impounding reservoir and estuarine reach of the river. Comparison with available field data is given. It was found that roughness of the underside of ice cover has very important effect on flow depth. In case of partial ice cover (border ice or ice-free channel) considerable increase of flow velocity was observed in the part of river cross- section with free surface.
Year: 1988