A study of the transportation of gravel by turbulent water flows
Thesis DisciplineCivil Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
Some aspects of the motion of gravel particles (> 2 mm) when entrained by water is considered. The flow is turbulent and the longitudinal slope, flat as in natural rivers. First a few field observations are described and it is shown how these observations conflict with existing theories for sediment transport. Secondly, a method for measuring the characteristics of turbulent water shearing at a rough boundary is described. The method involves measuring the velocity profile with a pitot tube and then finding the formula of best fit which is the form : [formula here]. Measurements were made and the technique is shown to be sufficiently precise. The results are analysed using a digital computer and are presented. Thirdly, a large number of entrainments were observed. Each entrainment was of a single glass ball from a specially prepared site on the rough bed. A careful analysis of the measurements made have enabled a number of firm conclusions to be drawn which relate to the mechanism of entrainment. Finally, a new mechanism of entrainment is postulated. The turbulence is considered as a large number of distinct rotating eddies. At the centre of each eddy is a small low pressure region and when it acts on a particle the eddy imparts a strong force to the particle. The effect is limited by the short time for which this force acts on the particle. Einstein has previously related entrainment to fluid pressure fluctuations, but the writer believes that the life forces are ten times as strong as those postulated by Einstein.