Scouring around a cylindrical bridge pier under partially ice-covered flow condition

Abstract

This thesis reports on the first step of an ongoing study of scouring around a cylindrical bridge pier under ice-cover conditions. Previous research confirmed that sediment transport decreases in ice-covered flow compared to free-surface flow. However, most of that research was conducted in a flow depth adjustment condition, maintaining constant the energy slope for both the ice-covered and the free-surface flow. This represents a valid hypothesis when an appropriate length scale is considered (i.e. long river reaches), but numerous other phenomena must be analyzed at a much shorter length scale: i.e. river reaches that contain abutments, bridge piers, cross-section alterations, tide bends, etc. According to Zabilansky et al. (1996--2002) findings, in these cases we can confirm that for an ice-covered flow in nature it is common to adjust faster the energy slope than the flow depth, thus, leading to drastic changes in the sediment transport and scouring behaviour. From a scouring point of view, when the flow depth has minor variations compared to the energy slope changes, the presence of an ice-cover significantly increases the flow velocities in the bottom half of the flow depth. As a result, a larger part of the flow energy is directed to the scouring process compared to the free-surface case. (Abstract shortened by UMI.)