Influence of Ice-covers on Stream Hydraulics and Geometric Characteristics of Alternate Bars in Rivers: an Experimental Study
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The thesis consists of two parts. In the first part (Chapters 2 and 3), the effect of ice-covers on stream hydraulics and especially the vertical velocity profile is reviewed (Chapter 2) and analyzed through a series of laboratory experiments involving both open channel and ice covered flows (Chapter 3). Chapter 3 aims to address the following research needs (1) examine and characterize velocity profiles in ice covered streams having a gravel bed, (2) evaluate existing equations (namely the two-power law by Tsai and Ettema 1994 and the equation by Guo et al. 2017) for the vertical velocity profile in covered flows, and (3) evaluate the modified log-wake law by Guo (2014) which is applicable to uncovered streams (open-channel) with smooth beds affected by the velocity-dip phenomenon. Use is made of simulated ice covers. The measured velocity profiles under the simulated ice covers were found to be in agreement with the general findings by other authors. The two-power law by Tsai and Ettema (1994) and the equation by Guo et al. (2017) were able to reproduce the velocity profiles resulting from the present measurements reasonably well, with the equation by Guo et al. (2017) yielding a more uniform distribution of the data around the best agreement line. For the open channel flows over smooth beds, the modified log-wake law by Guo (2014) was found to not be appropriate. A new empirical adjustment was proposed. Chapter 4 deals with the effects of ice-covers on the length and height of the bedforms known as alternate bars. The fundamental question this research aims to answer is whether or not the geometric characteristics of alternate bars are altered in the presence of an ice cover, and if yes, by how much? It was found that the height and especially the length increased with the presence of an ice cover. This chapter hypothesizes that in covered flows the effective width-to-depth ratio that determines the length and height of the bars may be that associated with the height of the lower layer (height of maximum velocity), instead of the total flow depth.