This dissertation presents a study on the development of a numerical model aimed at simulating free surface flow, which still remains an active research area. Modeling these processes is very challenging since the interface between air and water is characterized by sharp discontinuities in fluid properties and flow characteristics due to different densities, viscosities, surface tension and consequent discontinuities in spatial gradients of velocity and pressure. The constraint of incompressibility poses another difficulty on the efficient design of algorithms. Recently, the level set method has emerged as a powerful tool for evolving interfaces in computational science and engineering for a wide range of applications while the finite element method has been long known for its geometrical flexibility. An effort to combine these two methods is made in this study. Several benchmark problems are used for the test of the developed code in view of temporal and spatial accuracy. Then, the capability and efficiency of the model are extended with advanced turbulence models and parallel algorithm. The model is applied to problems of practical importance in hydraulics, including hydraulic jump under a sluice gate and the design of spillways for fish migration. The main focus is on the capturing of free surface and identifying and understanding of the vortical structures and nonhydrostatic pressure distribution. The model has proved to be very effective for these purpose. The new technique dealing with air-water interface in a more physically accurate way is introduced for future development and the new method is applied to the problems of static equilibrium for validation.

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.

" Estimating Life Loss for Dam Safety Risk Assessment" explores the need for a new life-loss model in dam safety risk assessment, historical foundations on which that model can be built, and issues that are critical for a successful life-loss model to address. After critiquing existing life-loss models, the work presents a summary of historical insights that were derived by characterizing flood events on the level of subpopulations at risk, using nearly l 00 carefully defined variables. Building upon both conceptual and historical insights, the work culminates by presenting the conceptual basis for a new life-loss model that remains under development. Chapter I introduces the topic of dam safety risk assessment and the central role that life-loss estimation plays in that field. Chapter II discusses important preliminary considerations in model development. Chapter Ill provides a detailed review of previous life-loss models that pertained to floods, including a critique of each. Chapter IV explores the DeKay-McClelland model in detail and raises serious concerns regarding its future use. Chapter V defines nearly l 00 variables and their respective categories for use in characterizing flood events. Chapter VI provides a detailed outline of historical insights that relate to flood events in one of 18 logical categories. Chapter VII proposes the framework for a new conceptual life-loss model-a model that is still under development and has yet to be refined or offered for testing-with sufficient details to indicate how it was developed and how it might be used. Chapter VIII provides a summary, conclusions, and recommendations for future research. Appendices A through D provide material related to over 900 pages of unpublished working documents developed while characterizing 38 flood events and nearly 200 subpopulations at risk. Appendix E offers a summary of existing software that, given additional development, might prove useful to life-loss estimation in dam safety risk assessment.

Earthen dams and levees create high gradients and increased hydraulic pressures in the underlying soil, which can lead to erosion and other challenges. Karst formations and other defects such as cracks in the foundation and/or abutments can lead to failure mechanisms such as internal erosion. Generally these voids or cracks are filled with soil, but due to the increased pressures and gradients that dams and levees create, the original soil is pushed out, thus creating a void that acts as a conduit for more soil to follow. Different soils will erode at different rates and some even create a natural filter, preventing further erosion from occurring, but due to these increased gradients and the cyclic changes that can occur throughout the seasons these filters can be broken down, allowing for erosion to continue and potentially lead to complete failure of the structure unless certain reparatory measures are taken. In the lab we have simulated different conditions that exist in the field and the results of testing a variety of soils can be found in this paper.

The Hyrum Project is located in northern Utah near the Cache County seat of Logan, and includes lands bordering the towns of Hyrum, Wellsville, and Mendon, Utah. The primary features of the project include a dam and reservoir on the Little Bear River, and three canals that total slightly more than 20 miles in length. Its principal purpose is to provide supplemental irrigation water to 6,800 acres of fertile land. This project is the result of several investigations relative to the improvement of water utilization in Cache County. A report prepared in 1922 entitled, "Report on the Utilization of the Land and Water Resources of Cache Valley, Utah," stimulated interest and concern over the insufficient water supply. Beginning with this report, and until the final approval of the project in 1933, various county, state, and federal agencies worked together to devise a feasible method of increasing the supply of irrigation water in Cache Valley.

The objective of this study is to provide a better understanding of suffusion characteristics of glacial soils and to present a simple yet reliable assessment procedure for determination of suffusion in the laboratory.Internal erosion by suffusion occurs in the core of an embankment dam when the ability of the soil to resist seepage forces is exceeded and voids are large enough to allow the transport of fine particles through the pores. Soils susceptible to suffusion are described as internally unstable. dams with core of broadly graded glacial moraines (tills) exhibit signs of internal erosion to a larger extent than dams constructed with other types of materials.The Suffusion behavior of glacial soils has been investigated through two different permeameter suffusion test have been employed, small scale permeameter and big scale permeameter. Details of the equipment along with its calibration, testing and sampling procedures are provided.The testing program were performed 9 test with different compaction degree in small scale permeameter and 2 test in big permeameter on internally stable categories of till soil. The categories are defined based on the soil grain size distribution and according to the methods developed by Kenney & Lau and Burenkova.Layers are identified with suffusion if the post-test gradation curve exhibit changes in distribution compared to the initial condition and also the tests revealed that the effect of grain size distribution and relative degree of compaction on the internal erosion susceptibility of glacial till soils at different hydraulic gradients

En la actualidad la Irrigación de Ite es abastecido por el río Locumba ubicado en la provincia de Locumba de la región Tacna. El río Locumba como todos los ríos de la costa del Perú, tiene su masa anual de agua concentrado en los meses de enero a marzo debido a las precipitaciones que se producen en la parte alta de la cuenca del río Locumba; razón a ello, existe excedentes de agua que se pierden en el Océano Pacifico por el sector de Ite; pero también en los meses de estiaje en el periodo de agosto a diciembre, el caudal del río Locumba disminuye y ocasiona déficit de agua para atender los requerimientos para uso agrícola de la irrigación Ite; razón a ello, muchas instituciones, como el Gobierno Regional de Tacna, la Municipalidad Distrital de Ite, la Dirección Subregional del Ministerio de Agricultura de Tacna, han efectuado diversos planteamientos para desarrollar proyectos de represamiento de agua del río Locumba. Bajo ése marco de referencia, en la presente investigación, se ha determinado la capacidad del embalse de la represa Ite en 7 MMC mediante el uso del software WEAP y los índices de confiabilidad en volumen y tiempo de abastecimiento de agua de la irrigación Ite. / At the present time Irrigation de Ite is absented by the Locumba river located in the Locumba province of the Tacna region. The Locumba River, like all the rivers of the coast of Peru, has its annual mass of water concentrated in the months of January to March due to the rainfall that occurs in the upper part of the Locumba river basin; reason to this, there is surplus water that is lost in the Pacific Ocean by the Ite sector; but also in the months of low water in the period from August to December, the flow of the Locumba River decreases and causes a water deficit to meet the requirements for agricultural use of the Ite irrigation; reason to this, many institutions, such as the Regional Government of Tacna, the District Municipality of Ite, the Sub regional Directorate of the Ministry of Agriculture of Tacna, have made various proposals to develop water damming projects of the Locumba River. Under this frame of reference, in the present investigation, the capacity of the reservoir of the Ite dam has been determined in 7 MMC through the use of WEAP software and reliability indices in volume and time of water supply of Ite irrigation. / Tesis

La resuspension de sédiments contaminés peut entraîner le relargage d'éléments traces métalliques (ETM) dans la phase dissoute. Pour anticiper le risque de remobilisation des ETM lors de la vidange des retenues de barrages et créer un modèle géochimique permettant de prédire ce risque, des expériences de resuspension de sédiments provenant de trois retenues ont été réalisées pendant une semaine dans un réacteur. Le pH et le potentiel redox ont été suivis en continu et des échantillons ont été prélevés afin de mesurer l'évolution des ETM dissous. Trois grandes tendances d'évolution des ETM ont été mises en évidence et ne sont pas modifiées par les variations des masses de sédiment en suspension (entre 2 et 9 g/L): 1) Cr, Cd et Zn ne sont pas relargués. 2) Mn, Fe Co, Pb, ainsi que As pour deux retenues, augmentent puis diminuent au cours du temps. Ces éléments sont contrôlés par les oxyhydroxydes de Fe et de Mn et l'évolution du potentiel redox dans la solution. 3) Mo, Al, ou As pour une retenue, continuent d'augmenter à la fin des expériences, révélant des processus de relargage plus lents et une stabilisation dans la phase dissoute. Dans les trois retenues, As est l'élément le plus fortement et durablement relargué. Ces données expérimentales ont été utilisées pour calibrer un nouveau modèle géochimique développé par EDF sur ECOLEGO, intégrant la cinétique des réactions d'échange des ETM entre la phase dissoute et trois types de phases solides: les oxydes, les particules organiques et les carbonates. La calibration des paramètres cinétiques permet de bien reproduire les évolutions temporelles des concentrations qui augmentent (relargage) puis diminuent (piégeage). / The resuspension of the contaminated sediments may promote the remobilization of trace metals to the dissolved phase, threatening the water quality. The dam reservoirs sometimes need to be fully drawn down and being able to anticipate the release of the contaminants is essential to improve the management of reservoirs and assess the risk of water quality degradation. Surface sediments were collected in three contaminated dam reservoirs and aliquots of wet sediments were resuspended for a week in a reactor. The pH and the redox potential were continuously measured, dissolved samples were collected and the evolution of dissolved trace elements concentrations were measured. Depending on the elements, different temporal trends can be highlighted during the resuspension experiments. These evolutions were reproducible, regardless of the mass of sediment used from 2 to 9 g/L. 1) Cd, Cr and Zn were not released; 2) Mn, Fe, Co, Pb and As for two reservoirs, increased and then decreased during the experiments and were regulated by the Fe- and Mn-oxyhydroxides and the redox potential; 3) Al, Mo, or As for one reservoir, were still increasing at the end of the experiments, showing slower release processes and the stabilization of these elements under dissolved forms. For theses three reservoirs, As showed the greatest and the most prolonged release during resuspension. The experimental trends of dissolved metals were used in the firts calibration steps of a new chemical speciation model developped by EDF, which takes several kinetic rates into account for the exchange reactions of dissolved metal between water and three types of solid phases.

Artificial destratification equipment was installed in Lake Samsonvale in October 1995 to reduce the biomass of potentially toxic cyanobacteria in the reservoir. This study was undertaken to investigate the effects of the destratifier on the limnological processes occurring in the lake and to determine if operation of the destratifier has been effective at reducing the summer populations of Cylindrospermopsis raciborskii and Microcystis aeruginosa. The study showed that artificial destratification of Lake Samsonvale has been successful at reducing the surface to bottom thermal gradient and increasing dissolved oxygen concentrations at depth. While the destratifier has not resulted in the lake becoming completely 'mixed' during summer, it has weakened resistance to mixing from meteorological events, which has led to a reduction in mean concentrations of total and dissolved phosphorus during summer. Although not conclusive, it is likely that the influence of the destratifier is restricted to a narrow radial distance around the bubbleplumes during periods of strong stability, so internal loading may continue to provide a substantial source of nutrients for cyanobacterial growth, particularly in regions of the lake less influenced by the destratifier. The results for cyanobacteria are less encouraging. Despite the reduction in concentrations of dissolved phosphorus, the destratifier has not been effective at reducing summer populations of C. raciborskii and M. aeruginosa. On the contrary, there is evidence to suggest that populations have actually increased which could have serious operational consequences for the lake by mixing the previously buoyant cyanobacteria to the level of the water off-take. The growth season for C. raciborskii has been extended by up to 3 months and population onset now occurs during spring. This increase in spring populations could be a result of significantly greater baseline populations during winter, or the earlier germination of akinetes as a result of increased sediment temperatures. The seasonal successional relationship between C. raciborskii and M. aeruginosa appears to have shifted from one of alternating dominance between the two species to one of co-existence under conditions of intermediate disturbance. It was concluded that although the continued operation of the destratifier may prove useful to minimise water treatment costs through reducing internal loading of dissolved constituents, it has not been successful in achieving its original objective of controlling cyanobacterial populations in the lake.

In case of exceptional floods induced by the failure of a dam, huge amounts of sediments may be eroded. This results in large-scale modifications of the valley morphology and may drastically increase the resulting damages. The objective of the research is to advance the understanding of sediment transport under dam-break flows. For such highly erosive and transient floods, it is crucial to account explicitly for sediment inertia, and therefore traditional “clear-water” modelling approaches are largely inappropriate. The present approach relies on a two-layer idealisation of the flow behaviour. Separating a clear-water flow region from the underlying sediment bed, the transported sediments are confined in a flow layer of finite thickness, endowed with its proper inertia, density and velocity. The thesis also pinpoints granular dilatancy as an essential mechanism of interaction between the layers. When passing from a solid-like to a fluid-like behaviour as they are entrained by the flow, the eroded sediment grains dilate along the vertical, and this generates vertical exchanges of mass and momentum that should be accounted for. The thesis proceeds first with experimental investigations. Laboratory dam-break waves are reproduced in a dedicated flume, exploring different bed configurations and sediment densities. Imaging observations are used to support the proposed phenomenological description of the flow. Within a shallow-water framework, theoretical and numerical endeavours are then developed to investigate the implications on the flow dynamics of the two essential contributions of the proposed description, i.e. the two-layer flow behaviour, and the effects of granular dilatancy.