Application of Sediment Transport Theory in Environmental Science and Engineering

Abstract

Sediment exists in different water bodies and its transport can be associated with different problems such as irrigation water contamination and infrastructure integrity compromise. Applying sediment transport theory helps better understand and solve these problems. Therefore, this dissertation reports on the experimental investigation of pathogenic microorganism resuspension and bridge pier scour based on sediment transport theory. The first research focused on the study of the resuspension of Escherichia coli and MS2 bacteriophage from bed sediment in irrigation canals. A set of laboratory experiments was conducted to investigate relation between the concentration of Escherichia coli and the MS2 in moving water and flow properties and the size of bed sediment. Results showed when bed material is sandy loam, their quantity in water increases with the shear stress on bed surface. However, for a sandy bed, their presence in water has no apparent correlation with flow properties. The amount of MS2 virus in water was greater at low flow velocity and shear stress than Escherichia coli because the size of the MS2 virus is much smaller. Finally, an empirical relation was formulated for calculating the maximum allowable Escherichia coli concentration in sandy loamy bed sediment. The second research focused on the investigation local scour around a group of three piers with different sizes, spacing, and attacking angles. The results of the scour pattern showed the sheltering effect of the upstream piers and interaction between horseshoe vortex and wake vortex. Based on the phenomenological theory of turbulence flow, an analytical equation was formulated for predicting the maximum scour depth. The significance of key parameters were evaluated using the statistical F-test. The coefficients in the equation were determined by the experimental data from this and other studies. The results showed pier diameter, pier spacing, actual pier width, flow depth, Froude number, and sediment size are important parameters for determining the maximum scour depth. The third research focused on the study of the turbulence flow field around the three pier group. Mean flow vectors, turbulence intensities were analyzed based on the instantaneous velocity measured by Acoustic Doppler Vectrino Profiler. Two pier spacings of 1 and 5 times the pier diameter and two attack angles of 0 and 30 were used to study the effect of pier spacing and attack angle on the flow field. A strong sheltering effect of upstream pier in tandem alignment was observed when piers spacing is small. Horseshoe vortices around the middle and downstream piers were enhanced when the piers were in staggered alignment. Distributions of bed shear stress showed that when the scour is in equilibrium, the bed shear stress in the scour hole is smaller than the approaching bed shear stress.