Author(s): Wojciech Majewski; Maria Baginska; Pawel Walczak
Linked Author(s): Wojciech Majewski
Keywords: No Keywords
Abstract: The presence of ice cover on rivers and impounding reservoirs changes flow characteristics to a great extent. The normal flow depth increases due to increased resistance resulting from an additional solid boundary. Calculations of water surface profile or discharge along a river reach with ice cover require detailed values of the roughness coefficient of the underside of ice cover. This coefficient may vary considerably with space and time depending on the character of ice cover, flow and meteorological conditions. Various methods have been proposed in the past to determine roughness coefficient of the underside of ice cover, composite roughness coefficient for the station and for the cross-section. The paper presents the method for determining roughness coefficient of the underside of ice cover based on direct measurements of velocity distribution in the flow under ice cover. Measurements of velocity distribution and obtained results are described. It is assumed that velocity distribution has logarithmic character in the regions near the bottom and ice cover. Calculating procedure includes the determination of logarithmic velocity distribution based on data from field measurements. The least mean square fit method is applied. Then average velocity, maximum velocity, Darcy -Weisbach friction factor for the underside of ice cover and finally Manning roughness coefficient are calculated. The same procedure can be applied for determination of bottom roughness coefficient. Roughness coefficients for the underside of ice cover were also determined from the known backwater profiles with ice cover using trial and error procedure. It was found that roughness coefficients of the underside of ice cover may be considerably higher than bottom roughness coefficients. The variation of roughness coefficients in space and time was also observed.
Year: 1988