Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Sturm, Terry; Committee Member: Burns, Susan; Committee Member: Webster, Donald. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 227-250).

Thesis (M.S.)--Florida State University, 2005. / Advisor: Wenrui Huang, Florida State University, FAMU-FSU College of Engineering, Dept. of Civil and Environmental Engineering. Title and description from dissertation home page (viewed Jan. 26, 2006). Document formatted into pages; contains xv, 123 pages. Includes bibliographical references.

Thesis (M.C.E.)--University of Delaware, 2009. / Principal faculty advisor: Jennifer Righman McConnell, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

This study investigates channel bed scour and fill as a result of individual flood events in a gravel-bed channel. Given the complexity of interactions between hydraulic force, the texture and arrangement of bed material, and input of sediment to a particular point of the channel bed, study objectives were pursued with the view that bed material movement is a stochastic phenomenon. A two-year field program was conducted in Carnation Creek, a small gravel-bed stream draining 11 km2 on the west coast of Vancouver Island, British Columbia. In the 900 m study reach, an array of measurement techniques, including scour indicators, magnetically-tagged stones, and conventional survey, yielded information about the fluctuations of the channel bed elevation and movement of scoured material for individual flooding periods. Frequency distributions of scour and fill depths associated with individual flooding periods are adequately modeled by negative exponential functions over the range of flood peak magnitudes observed in Carnation Creek. Analysis of scour depths measured in streams on the Queen Charlotte Islands demonstrates the applicability of the exponential model to flooding periods and flood seasons. Further, exploratory analysis suggests that a regional scour depth model is possible. Power functions relating mean depths of scour and fill to flood peak discharge show that depth increases with an increase in peak magnitude. Observed maximum scour depths in flooding periods are linked, in general, to streambed conditions influenced by antecedent flow conditions. These patterns in scour and fill exist within an overall pattern of increasing variability in depths of scour and fill as peak discharge increases. Evaluation of a heuristic model for mean travel distance as a function of particle size proposed by Church and Hassan (1992) provides convincing evidence for its general merit. Mean travel distance decreases inversely with particle size as size increases beyond the median diameter of subsurface sediment. This trend is consistent in both individual flooding periods as well as flood seasons. The majority of material finer than the median diameter of surface sediment is supplied from subsurface material, which influences the travel distances of these finer fractions because of burial. Computation of volumetric transport rates of bed material, based on the active scour depth and width of the channel bed, the virtual velocity of particle movement, and sediment porosity, suggests the potential for building scale correlations with streamflow, which have usually been defined by bedload sampling during floods. Error analysis indicates that determination of active width contributes most significantly to the imprecision of transport rate estimates. Results underscore the stochastic nature of sediment transport in gravel-bed channels. / Arts, Faculty of / Geography, Department of / Graduate

Traditional culvert designs, in many cases, have become habitat barriers to aquatic animal species. In response, environmentally sensitive culvert designs have been developed to function as ecological bridges. Bottomless and buried invert culverts are examples of such designs and are commonly used for fish passage. Additional design guidance specific to streambed stability in buried-invert or bottomless culverts under high flow events is needed. This study investigated incipient motion conditions for four substrate materials in a 2-ft (0.61-m) diameter circular bottomless arch culvert and in a 1-ft (0.30-m) wide rectangular flume in a laboratory setting. General scour of the streambed within the bottomless arch culvert was also investigated under partially pressurized and non-pressurized flow conditions. This thesis discusses the experimental methods used to determine incipient motion conditions and analyses of incipient motion prediction methods. This thesis also presents the experimental results obtained from both test facilities with the results of other published incipient motion studies on gravel streambeds. Finally, the prediction efficiency of eight stone sizing methods (open channel and culvert application) applied to the experimental results was analyzed, which may be useful for determining stable stone diameters to be used as riprap in simulated streambeds through bottomless culverts.

No / Computational Fluid Dynamics (CFD) represents a useful tool to study natural currents in the rivers and estuaries with erosive materials; therefore, it is always in the keen interest for scientists to further study and advance it, especially when numerical model has the advantages compared to actual laboratory experiment in terms of cost, time, and restrictions on conditions of the physical models and field collections. The present study deals with the hydro-morphological investigation and numerical modeling of a group of vertically stationed parallel groynes using FLOW-3D commercial software. To validate the results of the FLOW-3D simulation, it has been compared to the experiments from literature. Besides, a SSIIM 2.0 software has also been employed to compare with some of the FLOW-3D results. It was found that the accuracy of the FLOW-3D model influenced by the approach Froude number and the critical velocity ratio (Uavg/Ucr). Even though it underestimated the measured scour depth (due to complex and intense vortices, which reduce the accuracy of the numerical models), but general results from the model have reproduced the measured data well.

Erosional processes of solid materials have been the focus of many researchers around the world. Erosion can commence within a wide range of material strengths depending on the amount of water-driven energy and material properties. Erosion could also occur due to Aeolian effects as well as chemical weathering but these forcings are not of the focus of this research. Instead, the focus here is on rock erosion in waterways and in particular downstream of dams. Rock erosion mostly takes place at the downstream of dams where the water conveys through the spillbays from upstream to the downstream during an extreme event. This phenomenon threatens both the structural soundness of the dam with implications to the public safety. It usually occurs when the applied hydrodynamic forces (average and fluctuating) exceed the strength of the rock mass formation. Rock scour at the downstream of dams due to high velocity impinging jet is a complex and highly dynamic process. So a deeper understanding of the process is crucial to determine the rock scour rate and extent. Hydraulic laboratory models have been employed to investigate hydraulic processes and proved to be reliable tools for testing soil/sediment erosion; however, the study of rock scour remains challenging. The prototype rock formation cannot be utilized in the laboratory models because the flowing water in the scaled model contains much less energy and exerts less forcing. On the other hand, the use of granular sediment (non-cohesive), as a standalone approach to mimic the rock formation is not a precise method, since it will most probably lead to inaccurate results. The idea of using a mixture of granular and cohesive sediment is investigated here to adequately simulate the rock erosion process in the laboratory scaled models. The granular sediment represents the rock blocks while the cohesive additive is a binder to keep the granular sediment together. The rock scour process can occur through four mechanisms; fracture failure, block removal, fatigue failure and abrasion. In this study, because the focus is on the hydrodynamic forcing effects on rock erosion, we assume that in the completely and intermittently jointed rock, erosion is mostly governed by fracture, block removal and fatigue failure. Abrasion is triggered by collisional effects and is not the focus here. So, we hypothesize that if the rock formation considered being pre-fractured, it can be simulated using a mixture of non-cohesive sediment with cohesive additive. This method was utilized to assess the rock scour process at the downstream of the Priest Rapids Dam. The Priest Rapids Dam project was part of a series of projects that was conducted at IIHR-Hydroscience & Engineering at The University of Iowa and sponsored by the Public Utility District No. 2 of Grant County, Ephrata, Washington (GCPUD) to investigate juvenile salmonid migration at the Wanapum/Priest Rapids Development. It is a hydroelectric, concrete gravity, and mid-elevation dam owned and operated by Public Utility District No. 2 of Grant County, Washington (the "District"). To aid the District in their evaluation of fish passage, IIHR-Hydroscience & Engineering constructed comprehensive three-dimensional physical models of the forebay and tailrace of Priest Rapids Dam and a third model of spillbays 19-22 and powerhouse Unit 1 (sectional model). As part of the last phase of the project, it was crucial to assess the effects of the newly designed fish bypass system on the downstream rock foundation scour. To investigate this process, the 1:64 Froude-based scale tailrace model of the dam was utilized. The mixture of gravel, bentonite clay, and water was employed to mimic the rock formation and simulate the bedrock scour process in the model. Series of preliminary experiments were conducted to find the optimum mixture of gravel, bentonite and water to accurately replicate an existing scour hole observed in the prototype tailrace. Two scenarios were considered. First, tests were conducted to estimate the scour potential downstream of the fish bypass, which is currently under construction. Second, the scour potential downstream of the dam was also assessed for the Probable Maximum Flood (PMF) with the fish bypass system running. Based on the model tests results and observations, the simulated bedrock (mixture of gravel and cohesive bentonite) was able to replicate the rock scour mechanisms, i.e. fracture process, block removal and fatigue observed in nature. During the fish bypass scour tests, it was observed that the erosion process occurs in the form of block removal and fatigue failure. During the PMF scour test, instead, it was observed that the mixture is eroded in chunks of substrate. This process can be representative of fracture failure in rock which occurs when the induced pressure fluctuation exceeds the fracture strength or equivalently toughness of the rock. In the preliminary phase of this work it was recognized that a prerequisite for replicating the processes in the laboratory is the proper preparation of the mixture. There is limited information available in the literature about how much cohesive additive is required to simulate the erosional strength of the prototype rock formation. For this reason, in this study the effort has been made to develop a method to simulate the rock formation for studying rock scour process in the laboratory analog scaled models. To simulate the bedrock formation, various combination of granular sediment (gravel), cohesive additive, and water were created and tested. Choosing an appropriate cohesive additive concentration is critical and nearly a balancing act. An appropriate cohesive additive concentration should be cohesive enough to bind the material and not too strong to be eroded by the flowing water in the scaled models. Moreover, its properties should not change over time. Various cohesive additives can be mentioned i.e. kaolin clay, bentonite clay, cement, grease, paraffin wax. Among all of them, bentonite clay was chosen as the appropriate cohesive additive due to its swelling characteristic. When bentonite is mixed with granular sediment, it is restricted by the non-cohesive sediment grains. The bentonite expands to fill the voids and forms a tough, leathery mineral mastic through which water cannot readily move. In order to assess the erodibility of the mixture the Jet Erosion Test (JET) apparatus was used. The JET apparatus is a vertical, submerged, circular, turbulent impinging jet which is widely accepted and utilized to assess cohesive soil erosion through flow impingement. There are devices such as flumes which could be effectively used for bank erosion where the flow shear action is prevalent. In this study, it was sought important that the forcing replicated in the experiments was of the same nature (normal impinging forcing instead of shear forcing) as observed in the downstream end of a dam. For this reason, JET was chosen as it provided a larger range of stresses (ranging between 100-1000 Pa) comparing to the flume device. The apparatus was designed based on the device developed by Hanson and Hunt (2007) and built at the IIHR-Hydroscience & Engineering. Various replicate samples were made with different combinations of gravel, sodium bentonite clay, and water. To determine the erosional strength of the samples (critical stress) they were tested using the JET apparatus. The critical stress was determined as the stress associated with zero eroded mass. The results revealed that the erosional strength of the simulated bedrock mixtures highly depends on the amount of adhesive component (bentonite clay). The mixtures with the higher percentage of bentonite clay are less susceptible to erosion. The erosion threshold plot - similar to Annandale's plot - for the simulated bedrock mixtures was developed. Using the erosional strength of the simulated bedrock mixtures, a step-by-step systematic method was developed to determine the optimum combination of weakly cohesive substrate in order to simulate the strength of the prototype bedrock. The method is based on the Annandale's erodibility index method and requires information about the prototype bedrock strength (erodibility index). The method is explained in conjunction with the Priest Rapids Dam project example. The old trial and error method to establish an optimum weakly cohesive substrate is costly and time consuming especially in the case of large scale laboratory models. Also, the applicability of the method would be questionable when there is not enough information or a past data set that can be used as a baseline (witness) test. The new method eliminates these problems and the optimum mixture can be established using the geological information of the prototype bedrock formation.

Three-dimensional scour propagation along offshore pipelines is a major reason to pipeline failures in an offshore environment. Although the research on scour in both numerical and experimental aspect has been extensive over the last three decades, the focus of the investigation has been limited to the two-dimensional aspect. The knowledge on three-dimensional scour is still limited. This dissertation presents the results of an experimental investigation on threedimensional scour along offshore pipelines in (1) steady currents (2) waves only and (3) combined waves and current. The major emphasis of the investigation is to investigate the propagation of the scour hole along the pipeline after the initiation of scour. Physical experiments conducted were used to quantify the effects of various parameters on scour propagation velocities along the pipeline. The problem of monitoring real time scour below a pipeline was solved by using specifically developed conductivity scour probes. Effects of various parameters such as pipeline embedment depth, incoming flow Shields parameter, Keuglegan- Carpenter (KC) number and flow incident angle to the pipeline on scour propagation velocities along the pipeline were investigated. The investigations clearly reveal that scour propagation velocities generally increase with the increase of flow but decrease with the increase of the pipeline embedment depth. A general predictive formula for scour propagation velocities is proposed and validated against the experimental results. There are still some common issues related to pipeline scour that is lacking in the literature to date. One of these issues is the effects of Reynolds number on two-dimensional scour beneath pipelines. A numerical approach was adopted to investigate the Reynolds-number dependence of two-dimensional scour beneath offshore pipelines in steady currents. A novel wall function is proposed in calculating the suspended sediment transport rate in the model. The effects of Reynolds number were investigated by simulating the same undisturbed Shields parameters in both model and prototype but with different values of Reynolds number in two separate calculations. The results revealed that scour depths for prototype pipelines are about 10~15% smaller than those for model pipelines. The normalized time scales was found to be approximately the same, and the simulated scour profiles for the model pipelines agree well with the experimental results from an independent study. The backfilling of pipeline trenches is also an important issue to the design and management of offshore pipelines. A numerical model is developed to simulate the self-burial of a pipeline trench. Morphological evolutions of a pipeline trench under steady-current or oscillatory-flow conditions are simulated with/without a pipeline inside the trench. The two-dimensional Reynolds-averaged continuity and Navier-Stokes equations with the standard k-e turbulence closure, as well as the sediment transport equations, are solved using finite difference method in a curvilinear coordinate system. Different time-marching schemes are employed for the morphological computation under unidirectional and oscillatory conditions. It is found that vortex motions within the trench play an important role in the trench development.

Scour at bridge piers is considered as a significant safety hazard. Hence, scour countermeasure design plays a critical role to hinder the scour potential at bridges. The selection methodology for a scour countermeasure varies with respect to site conditions, economy, availability of material and river characteristics. The aim of this study is to review the literature on this topic to gather universally accepted design guidelines. A user-friendly computer program is developed for decision-making in various sequential steps of countermeasure design against scouring of bridge piers. Therefore, the program is eventually intended to select the feasible solution based on a grading system which deals with comparative evaluation of soil, hydraulic, construction and application aspects. The program enables an engineer to carry out a rapid countermeasure design through consideration of successive alternatives. A case study is performed to illustrate the use of this program.