The Shield&rsquo / s Diagram has been the key stone for the description of initiatial motion of a particle in open channel flow. Data in Shield&rsquo / s study and further studies are collected in channels. However, the approximation of these data for the case of withdrawal of sediment or clean water through bottom outlets has not been confirmed. Furthermore, two phase models run to simulate the phenomenon so far have used brine and water combination. In this study, an experimental attempt is made to study the behavior of deposits subject to withdrawal from a bottom outlet where there are not enough parameters to calculate the bottom shear stress and consequently the dimensionless parameters generally used for the description of initiation of motion. The experimental set up used for this purpose is a 1 m long and 0.35 m wide channel such that at the downstream of the channel there is a horizontal slit representing the bottom outlet. During the experiments, fresh water and sand with D50 = 0.298 mm and D50 = 0.912 mm are used. Two different widths of the slit, namely 0.35 m and 0.0875 m are investigated. Based on the observations of the incipient motion of the sediment, the findings in the form of a relationship among the discharge through the bottom outlet, and some other relevant parameters are reported. In addition, a comparison of these data with the literature by the help of some newly defined dimensionless parameters for the description of the initiation of motion is included.

A series of relatively recent bridge failures due to pier scour, as reported in literature, has rekindled interest in furthering our understanding of the scour process and for developing improved ways of protecting bridges against scour. Moreover, increased attention is being given to the state of Canadas infrastructure, a major aspect of which is the transportation network. In part, there is concern about both the impact of a failure on the handling of traffic flow while the failure is being remedied and on the cost of replacing the failed system component. As such, attention is being given to the scour design of new bridges and to the inspection, maintenance and management of existing bridge structures. The two major countermeasure techniques employed for preventing or minimising local scour at bridge piers are increased scour resistance and flow alteration. In the former case, the objective is to combat the erosive action of the scour-inducing mechanisms using hard engineering materials or physical barriers such as rock riprap. In the latter case, the objective is to either inhibit the formation of the scour-inducing mechanisms or to cause the scour to be shifted away from the immediate vicinity of the pier. This research focuses on a particular application of the latter technique. <p> In this study, the use of collars for reducing the effects of local scour at a bridge pier is presented together with the time aspect of the scour development. The adoption of a collar is based on the concept that its existence will sufficiently inhibit and/or deflect the local scour mechanisms so as to reduce the local scour immediately adjacent to the pier. The overall objective of the research is to study the temporal development of the scour for a pier fitted with a collar and a pier without a collar. More specifically, the objectives are: i) to evaluate the effectiveness of a pier collar for mitigating the depth of scour that would otherwise occur at a bridge pier; and ii) to assess the occurrence of an equilibrium scour condition, if achieved, or of the implications of not achieving such a condition in respect of interpreting the results obtained from a physical hydraulic model study. <p>The study was conducted using a physical hydraulic model operated under clear-water conditions in cohesionless bed material. Tests were conducted using two different pier diameters so as to determine the effect of pier diameter on the temporal development of scour for a plain pier. Also investigated was the effect of collar size on the time development of scour and its efficacy at preventing scour at a bridge pier. The time development of the scour hole around the model pier with and without a collar installed was compared with similar studies on bridge piers. Several equations for the temporal development of scour depth and those for the prediction of the equilibrium scour depth were tested as part of this study. <p>The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. The depth of the scour hole increases as the duration of the increased flow that initiates the scour increases. The extent of scour observed at the pier also increases as the duration of the tests increases. It was found that the temporal development of the scour hole at the pier was dependent on whether or not the pier was fitted with a collar placed at the bed level. The pathway to an equilibrium scour depth is different depending on whether the pier is fitted with a collar or not. With a collar in place, the development of the scour hole is considerably delayed. A truly equilibrium scour condition is not readily attainable and was not achieved in the work reported herein. It was demonstrated that wrong conclusions may be reached if a test is stopped short of an equilibrium state. As regards the temporal development of scour depth and for the tests in which no collar was fitted to the pier, it was noted that the form of equation that fits the experimental data well was the one given by Franzetti et al. (1982). Furthermore, it is possible to reach a variety of conclusions about the efficacy of using collars as a pier scour countermeasure technique, depending on which definition of time to equilibrium scour is adopted.

A series of relatively recent bridge failures due to pier scour, as reported in literature, has rekindled interest in furthering our understanding of the scour process and for developing improved ways of protecting bridges against scour. Moreover, increased attention is being given to the state of Canadas infrastructure, a major aspect of which is the transportation network. In part, there is concern about both the impact of a failure on the handling of traffic flow while the failure is being remedied and on the cost of replacing the failed system component. As such, attention is being given to the scour design of new bridges and to the inspection, maintenance and management of existing bridge structures. The two major countermeasure techniques employed for preventing or minimising local scour at bridge piers are increased scour resistance and flow alteration. In the former case, the objective is to combat the erosive action of the scour-inducing mechanisms using hard engineering materials or physical barriers such as rock riprap. In the latter case, the objective is to either inhibit the formation of the scour-inducing mechanisms or to cause the scour to be shifted away from the immediate vicinity of the pier. This research focuses on a particular application of the latter technique. <p> In this study, the use of collars for reducing the effects of local scour at a bridge pier is presented together with the time aspect of the scour development. The adoption of a collar is based on the concept that its existence will sufficiently inhibit and/or deflect the local scour mechanisms so as to reduce the local scour immediately adjacent to the pier. The overall objective of the research is to study the temporal development of the scour for a pier fitted with a collar and a pier without a collar. More specifically, the objectives are: i) to evaluate the effectiveness of a pier collar for mitigating the depth of scour that would otherwise occur at a bridge pier; and ii) to assess the occurrence of an equilibrium scour condition, if achieved, or of the implications of not achieving such a condition in respect of interpreting the results obtained from a physical hydraulic model study. <p>The study was conducted using a physical hydraulic model operated under clear-water conditions in cohesionless bed material. Tests were conducted using two different pier diameters so as to determine the effect of pier diameter on the temporal development of scour for a plain pier. Also investigated was the effect of collar size on the time development of scour and its efficacy at preventing scour at a bridge pier. The time development of the scour hole around the model pier with and without a collar installed was compared with similar studies on bridge piers. Several equations for the temporal development of scour depth and those for the prediction of the equilibrium scour depth were tested as part of this study. <p>The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. The depth of the scour hole increases as the duration of the increased flow that initiates the scour increases. The extent of scour observed at the pier also increases as the duration of the tests increases. It was found that the temporal development of the scour hole at the pier was dependent on whether or not the pier was fitted with a collar placed at the bed level. The pathway to an equilibrium scour depth is different depending on whether the pier is fitted with a collar or not. With a collar in place, the development of the scour hole is considerably delayed. A truly equilibrium scour condition is not readily attainable and was not achieved in the work reported herein. It was demonstrated that wrong conclusions may be reached if a test is stopped short of an equilibrium state. As regards the temporal development of scour depth and for the tests in which no collar was fitted to the pier, it was noted that the form of equation that fits the experimental data well was the one given by Franzetti et al. (1982). Furthermore, it is possible to reach a variety of conclusions about the efficacy of using collars as a pier scour countermeasure technique, depending on which definition of time to equilibrium scour is adopted.

Non-overflow flow-through rockfill structures are river engineering elements used to attenuate and delay inflow hydrographs. They represent expedient places to deposit rather enormous quantities of waste rock at mountainous mine sites. Their application has become so common that matters of safety regarding their design have been laid out in Section 8.5 of the Canadian Dam Safety Guidelines (CDA 2007). The research described herein was directed at investigating the different aspects of the hydraulics of these flow-through rockfill structures. In order to assess the potential for an unraveling failure of flow-through rockfill dams, a systematic study of the hydraulic design of these structures was conducted and the non-linear nature of flow through these structures was dealt with using a p-LaPlacian-like partial differential equation. Subsequently, factors of safety against this type of failure are presented for a range of downstream slopes, thus showing the unsafe combinations of embankment slope and particle diameter. Three different index gradients within the toe of such structures were investigated. In this regard, the gradient most suitable for independently computing the height of the point of first flow emergence on the downstream face is examined and a method for independently computing the variation in hydraulic head within that vertical (which allows for the toe of the structure to be isolated) is presented. An additional gradient that allows for the independent estimation of the default tailwater depth is proposed. In order to provide better tools to assess the behavior of these embankments at the toe, laboratory and analytical studies were undertaken. In this regard, the hydraulics associated with the zone of the downstream toe were studied. The depth variation of the seepage-face was computationally modeled, and two approaches for solving the spatially varied flow (SVF) condition problem within the toe region undertaken. The results show that a dual linear variation in depth can be used to good accuracy, without inducing any unrealistic exit gradients in the zone of primary concern with respect to unraveling. It is hoped that these techniques and computational tools provided herein will aid in facilitating the design and assessment of these flow-through rockfill structures.