Les rivières présentent généralement un lit ondulé dû à la présence de bancs, qui correspondent à des larges dépôts sédimentaires alternant avec des zones profondes (mouilles). Des travaux d'ingénierie importants et répétés modifiant la géométrie du cours d'eau, le régime hydraulique et l'apport sédimentaire peuvent à terme modifier la dynamique des bancs à l'échelle de la rivière. Une meilleure compréhension des processus liés aux bancs est importante pour les gestionnaires des rivières, car les bancs contrôlent activement la morphologie du lit et érodent les berges, impactant la navigation, les prises d'eaux, les ouvrages et la qualité des habitats. Même si les mécanismes régissant la formation et le développement des bancs sont bien compris, la compréhension de la morphodynamique des bancs en milieu fluvial reste limitée, en raison de la non-linéarité induite par la combinaison de facteurs naturels en atrophiques. La non-uniformité des sédiments est une caractéristique inhérente des rivières, mais son impact sur la propriété des bancs, même dans des cas simplifiés, reste obscure. Ce travail de thèse vise à étudier l'impact de l'hétérogénéité granulométrique sur des bancs dans des chenaux endigués, via l'utilisation d'un modèle morphodynamique bi-dimensionnel implémenté dans le système Telemac-Mascaret. Les développements numériques nécessaires sont apportés afin d'être en accord avec l'état de l'art sur la modélisation de bancs avec un sédiment-non-uniforme. Par la suite, ce modèle est utilisé pour l'étude de la morphodynamique des bancs dans un chenal rectiligne sur la base d'expériences réalisées en laboratoire. Finalement, l'analyse est transférée sur un tronçon de 1 km de la Loire, caractérisé par sa géométrie relativement complexe. Les résultats permettent de valider l'approche de modélisation et démontrent la portabilité pour d'autres études, apportent plus d'éléments sur la relation entre sédiment non-uniforme et les bancs, et pourront être utilisés pour préconiser les gestionnaires des rivières / Rivers often present a wavy bed topography due to the presence of bars, corresponding to large sediment deposits alternating with deeper areas (pools). Intense and continual river engineering works altering the river geometry, flow regime and sediment supply can impact bar morphodynamics at the reach scale. A deep knowledge of bar processes is important for river managers, because bars actively control the river bed topography and influence bank erosion, with consequences for navigation, water intakes, infrastructure and the quality of their habitats. Although the origin of bar formation and propagation is well understood, the understanding of bar morphodynamics in rivers remains limited due to the non-linearity of combined natural and anthropogenic effects. Sediment non-uniformity is an inherent characteristic of rivers, but its impact on bar properties, even considering simple configurations, is still unclear. This Ph.D. thesis aims at investigating the impact of sediment size heterogeneity on bars in rivers with non-erodible banks, using a two-dimensional morphodynamic model implemented in the Telemac-Mascaret system. The necessary model developments are brought to comply with the state of the art on the modelling of heterogeneous sediment with bars. Then, the model is used to study bar morphodynamics in a straight channel on the basis of laboratory experiments. Eventually, the analysis is transferred in a 1 km reach of the Loire river characterized by a relatively complex geometry. General outcomes validate the modelling approach and demonstrate the application portability for other study cases, shed more light on the relationship between non-uniform sediment and bars, and can be later used as recommendations for river managers.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 160-168).

Les aménagements hydrauliques du Rhin ont fortement modifié le fonctionnement hydrologique des zones alluviales et provoqué la déconnexion de la plupart des bras du Rhin et des forêts alluviales. Des opérations de ré-inondation des secteurs déconnectés du fleuve ont été menées dans un objectif à la fois de rétention de crue et de submersion écologique qui devraient permettre à ces zones de retrouver tout ou partie de leur fonctionnalité. Le polder d’Erstein est un secteur forestier expérimental pour le suivi de l’impact des ré-inondations des zones alluviales. Les inondations du polder par les eaux de Rhin sont susceptibles d’en modifier le fonctionnement hydrologique (écoulements de surface, échanges nappe-rivière, recharge de la nappe …). L’objectif général de ces recherches est l’analyse et la quantification des transferts hydriques dans un aquifère poreux dans un contexte de ré-inondation. Pour ce faire nous avons réalisé des simulations numériques de l’écoulement à l’aide du code de calcul Feflow (Finite element subsurface flow system), qui ont été validées par les données hydrogéologiques mesurées in situ. Ce travail est organisé en cinq volets. Le point de départ est un état de l’art du fonctionnement, de la structure des zones alluviales et des mécanismes du transfert hydrique dans ces zones. La deuxième partie, fournit une présentation détaillée du site expérimental sur lequel une mission de suivi scientifique a débuté en 2003 et ainsi fourni une importante base de données hydrologiques (eaux de surface et eaux souterraines). Ces données ont servi à caractériser les écoulements d’eau en zone non saturée. La troisième partie est consacrée à la construction du modèle hydrodynamique. Compte tenu de l’importance du réseau des anciens bras du Rhin alimentées par la nappe existant à l’intérieur du polder, la question des échanges cours d’eau-nappe a été abordée. Hormis la recharge de la nappe par les cours d’eau, une part importante de l’infiltration d’eau depuis la surface du sol lors des inondations contribue à la recharge. Pour quantifier cette part, nous avons développé une approche pédologique originale afin de caractériser les hétérogénéités des sols par des paramètres hydrodynamiques. Ces hétérogénéités qui varient spatialement sur le polder ont une influence significative sur les flux verticaux et les temps de résidence de l’eau dans la zone non saturée. Les résultats obtenus en 1D ont ensuite été appliqués à toute la superficie du polder d’Erstein avec l’objectif de quantifier l’ensemble des écoulements à cette échelle. Différents scénarios d’hétérogénéité proposés se fondent sur une complexification de la structure de l’aquifère poreux, afin d’évaluer l’impact des hétérogénéités du sol sur le transfert hydrique dans le polder d’Erstein. / The hydraulic management of the Rhine has drastically modified the hydrological functioning of alluvial zones and caused the disconnection of most side-channels of the Rhine and alluvial forests. The re-flooding restoration works of the disconnected sectors are planned with objective of both the retention of flood and of ecological flooding which should allow these zones to recover all or part of their functionality.The Erstein polder is a forested experimental area for monitoring the impact of the alluvial zones re-flooding. The flooding of the Rhine plain may modify its hydrological functioning in terms of runoff, groundwater-river exchanges and groundwater recharge. Our general objective is to analyze and quantify water flux in an unsaturated porous aquifer. Therefore, based on the given hydraulic and hydrogeological conditions of the study site, we performed numerical flow simulations using the finite element model Feflow 5.3.This work is structured in five chapters. The starting point is a state of the art about the functioning and the structure of alluvial zones and the mechanisms of water flux in these areas. The second chapter presents the experimental site. A scientific monitoring mission has been implemented on the polder site and an extensive data base of hydrological measurements (surface and groundwater) was created. This data base was used to characterize the water flux in the unsaturated zone. The third chapter is devoted to the construction of the hydrodynamic model. Given the importance of the side channels network supplied by the existing groundwater inside the polder, the water exchange between surface water and groundwater was discussed. Apart from the groundwater recharge by streams, a significant infiltration of water from the soil surface during flooding contributes to groundwater recharge. To quantify this part, we developed an original approach in order to characterize the heterogeneities of soils using hydrodynamic model parameters. These heterogeneities that vary spatially on the polder have a significant influence on the vertical flow and the residence time of water from the ground surface to the groundwater. The results obtained in 1D were then used to model the influence of soil heterogeneities of the entire area of the study site on water infiltration during inundation event and groundwater recharge. Different scenarios of heterogeneity were used to render the structure of the porous aquifer progressively more complex in order to evaluate the impact of the heterogeneities on water flux in the vadose zone of the Erstein polder.

Ninety-eight percent of water taken from the Mississippi River Shallow Alluvial Aquifer, hereafter referred to as “the aquifer” or “MRVA,” is used by the agricultural industry for irrigation. Mississippi Delta agriculture is increasingly using more water from the MRVA and the aquifer has been losing about 300,000 acreeet per year. This research expands on previous work in which a model was developed that simulates the effects of climatic variability, crop acreage changes, and specific irrigation methods on consequent variations in the water volume of the MRVA. This study corrects an identified problem by replacing total growing season precipitation with an irrigation demand driver based on evaporation and crop coefficients and changing the time scale from the entire growing season to a daily resolution. The calculated irrigation demand, as a climatological driver for the model, captures effective precipitation more precisely than the initial growing season precipitation driver. Predictive equations resulting from regression analyses of measured versus calculated irrigation water use showed R2 and correlations of 0.33 and 0.57, 0.77 and 0.88, 0.71 and 0.84, and 0.68 and 0.82 for cotton, corn, soybeans and rice, respectively. Ninetyive percent of the predicted values fall within a range of + or - about 23,000 acreeet, an error of about 10-percent. The study also adds an additional conservation strategy through the use of surface water from onarm reservoirs in lieu of groundwater. Analyses show that climate could provide the entire water need of the plants in 70-percent of the years for corn, 65-percent of the years for soybeans and cotton, and even 5-percent of the years for rice. Storing precipitation in onarm structures is an effective way to reduce reliance of Delta producers on groundwater. If producers adopted, at a minimum, the 97.5:2.5 ratio suggested management practice, this minimal management strategy could potentially conserve 48-percent, 35-percent and 42-percent of groundwater for cotton, corn and soybeans, respectively. Even in extreme drought years such as 2007, cotton, corn and soybeans produced under the 97.5:2.5 management strategy could conserve 32-percent, 46-percent and 38-percent of groundwater, respectively.

No description available.

The aim of the research is to assess the sustainability of groundwater supply and the suitability of hand-drilling techniques for accessing groundwater for irrigation practices along the shallow alluvial floodplains of River Benue, NE Nigeria. Hand-drilling techniques are affordable means for the farmers to abstract water from these shallow aquifers. Determining the most sustainable hand-drilling techniques (taking into account the hydrology and sedimentology of the floodplain) will improve farming activities and food security in this region and the country at large. Hydrological data (obtained from fieldwork and modelling) demonstrate that the River Benue is the main source for recharge of the shallow alluvial aquifers of the floodplain during the dry season period. Water table heights were estimated by resistivity survey using ABEM Terrameter equipment and measured by automatic piezometer instruments. Floodplain sedimentology and hydrogeology were assessed at seventeen natural riverbank outcrops and twelve hand-drilled boreholes. At each location, sediment samples were collected from every exposed sedimentological unit. Locations and elevations were measured using a ProMark3 dual frequency GPS instrument, to create a detailed topographic map with updated contours. Twenty-four electrical resistivity sounding profiles and twelve-groundwater measurement were also obtained to explore the groundwater level of the floodplain. The resistivity results confirm the availability of water in the alluvial aquifers of the floodplain. In order to determine the most appropriate hand drilling techniques, a Field Shear Vane Tester was used to measure sediment shear strength at twelve different borehole locations. Shear strength forces were higher on clayey silt and sandy silt, and lower on sand formations. It appeared that in some areas of the floodplain, the farmers are already above the shear strengths that can be provided by human power. Hence, any increase of the hardness of the surface of the sediment would make low-cost hand drilling impractical. Particle size analysis for the sediment samples showed that the samples were largely sandy in nature, which enables easy movement of water through the layers for aquifer recharge. Magnetic susceptibility (used to classify the source of sediment and the process of their formation) revealed that the main source of the sedimentary materials was upstream of the study site and varies little over time. The groundwater level of the study area decreased away from River Benue valley during the dry season period. One perched aquifer formations and possibly two others were observed in three different locations, which reflects a low-permeability stratigraphic unit (such as lens of clayey silt) within alluvial sands. These should be avoided by farmers, as they are likely to provide water only in the short-term. Finally, groundwater modelling was undertaken (with various scenarios) for the River Benue floodplain using acquired sedimentology and hydrology data integrated into MODFLOW software. The results revealed that low-cost hand-drilling techniques such as augering and jetting remain possible for abstracting the shallow alluvial aquifers on the floodplain for irrigation farming in the study area, unless the most likely low river water stages in River Benue, over-exploitation of the shallow alluvial floodplain groundwater and drought scenarios occur.

Sediment delivery to a basin exerts a first-order control over sedimentation, and therefore study of sedimentary rocks can reveal information about the nature of sediment delivery in the past. This dissertation examines several aspects of this problem using experimental, outcrop, and subsurface data. Flume experiments were undertaken to test the combined effects of autogenic alluvial aggradation and forced regression on the development of fluviodeltaic stratigraphy. Alluvial aggradation occurred in response to steady relative sea-level fall, and eventually consumed the entire sediment budget as the river lengthened in response to forced regression. The Campanian Lower Castlegate Sandstone (Utah) was studied as a potential ancient analog resulting from similar autogenic behaviors as observed in the experiments. Extensive measurement of grain-size distributions and paleo-flow depths from outcrop were utilized to explore downstream changes in paleo-hydraulics of the ancient fluvial systems in the Lower Castlegate in response to extensive alluvial aggradation and consequent loss of sediment from transport. An interesting finding was the stratigraphic signature of backwater hydraulic conditions in the distal reaches of the Lower Castlegate paleo-rivers. Finally, a simple and novel inversion scheme was developed for estimating paleo-sediment flux from ancient shelf-margin successions. An advantage of the methodology is that it allows for both spatial and temporal reconstruction of paleo-sediment flux patterns. The inversion scheme was applied to shelf-margin successions in the Washakie-Sand Wash Basin of Wyoming, the New Jersey Atlantic margin, the North Slope of Alaska, and the Zambezi margin of East Africa using published subsurface datasets. The Neogene passive margins within the studied datasets were found to consistently deposit around one-third of their total sediment budget on the shelf-margin topset, and bypass two-thirds of their budget beyond the shelf edge. The implications of this finding on the flux of terrestrial-derived particulate organic carbon (POC) from rivers to the ocean were explored, and a long-term average flux of POC to deepwater storage was estimated. The sediment-flux inversion scheme was also applied to derive input parameters for stratigraphic modeling of the Ebro margin. The modeling results indicate that the autostratigraphic behavior of the margin may have been previously underestimated. / text

Soil degradation is a complex process which may occur anywhere and at any time. It directly affects the physical, chemical and biological processes within the soil profile. Soil degradation can either be as a result of natural hazards or due to manmade actions, such as mismanagement on cropping patterns, soil preparation and cultivation practices. Regardless of how it is caused, soil degradation has strong negative effects on plant and soil productivity. Soil degradation can accelerate a series of processes such as erosion, compaction, loss of organic matter, loss of whole soil biota, surface sealing and contamination. This thesis presents the assessment of soil properties to improve our understanding of soil degradation on raised-bed orchards in the Vietnamese Mekong delta (MD). Measurements were made on 10 citrus plantations which had been established during a range of years from 1970 to 1998 at Hau Giang province. Soil sampling was made in the dry season of 2010 at two soil depths for each raised-bed to determine soil chemical and physical properties. The soil penetration resistance (PR) was periodically measured once a week together with soil sampling for moisture measurements during a period of 5 months. Analysis indicated the pH value of the soil was tending to decrease, nutrient imbalance and deficiency was developing, and the soil structure was deteriorating during the age since the raised-beds were originally constructed. Preventive and restorative measures need to be considered for restoring and retaining the quality of the soil and the ground water. These measures should consist of (1) neutralizing of excess acidity, (2) balancing of nutrients, (3) maintaining of soil organic matter, and (4) application of appropriate irrigation schedules. / Suy thoái đất là một tiến trình phức tạp xuất hiện ở mọi nơi, mọi lúc làm tác động trực tiếpđến các quá trình lý, hóa và sinh học trong phẫu diện đất. Nó có thể là kết quả của các hoạtđộng do tự nhiên hoặc do con người như sử dụng sai hoặc thực hành quản lý đất đai bất hợplý. Cho dù nguyên nhân thế nào chăng nữa, suy thoái đất cũng gây ra các ảnh hưởng bất lợinặng nề lên cây trồng và sức sản suất của đất. Suy thoái đất có thể thúc đẩy hàng loạt cácquá trình như là xói mòn, nén dẽ, mất vật liệu hữu cơ và sinh vật đất, đóng váng bề mặt vàô nhiễm. Luận văn này trình bày sự đánh giá về các đặc tính của đất để mở mang sự hiểubiết về suy thoái đất trên các vườn cây ăn trái ở đồng bằng sông Cửu Long. Thí nghiệmthực hiện trên 10 vườn cam quít với khoảng thời gian thành lập vườn từ 1970 đến 1998 tạitỉnh Hậu Giang. Mẫu đất được lấy vào mùa khô năm 2010 ở hai độ sâu cho mỗi vườn đểphân tích các chỉ tiêu lý hóa đất. Sức kháng xuyên của đất được đo định kỳ mỗi tuần kếthợp với lấy mẫu để xác định ẩm độ đất trong suốt khoảng thời gian 5 tháng. Kết quả phântích cho thấy pH đất có khuynh hướng giảm, sự thiếu và mất cân bằng dinh dưỡng đất ngàycàng lộ rõ, và cấu trúc đất đang xấu đi theo độ tuổi của vườn. Các biện pháp phòng ngừa vàphục hồi cần được quan tâm đối với việc phục hồi và duy trì chất lượng của đất và nướcngầm. Các biện pháp nên bao gồm (1) trung hòa độ chua đất, (2) cân bằng dinh dưỡng, (3)duy trì vật liệu hữu cơ trong đất, và (4) áp dụng chế độ tưới thích hợp. / <p>QC 20130909</p>

Made available in DSpace on 2017-07-10T17:30:29Z (GMT). No. of bitstreams: 1 Leandro_Oliveira.pdf: 7284550 bytes, checksum: f70fdc0eab04270115ab2fbaf7a5f445 (MD5) Previous issue date: 2014-03-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Alluvial fans are good indicators of environmental change and tectonic movement. Thus, it is proposed to investigate which factors influenced the alluvial fan at the mouth of 1st order channel of Chopim River basin at Paraná State. For this, the objectives were 1) identify evidence of neotectonic; 2) characterization stratigraphic units, 3) identification depositional physical processes; 4) seeking records of vegetation change and 5) establish chronological correlation with global events. As a methodological procedure was carried out: 1) field work; 2) laboratory work and 3) office work. The field work consisted of: a) establishment of the stratigraphic section HS12, descriptions and sampling of materials; b) topography in drainage basin of 1st order channel on alluvial fan; c) electromagnetic and manual surveys on the deposit of alluvial fan and d) structural survey on the slope. The laboratory work for the stratigraphic section HS12 on the bedside of the alluvial fan included: a) particle size analysis of the matrix; b ) reason of stable isotopes of carbon 13/12 (δ¹³C) and c) radiocarbon dating (14C). In relation to work in the office was held activities such as: a) treatment of grain size data of matrix by Sysgran; b) organization and interpretation of field descriptions and laboratory; c) photointerpretation and d) GIS. Based on the results, it is concluded that the evolution of alluvial fan occurs from 2 main times. In the first time, it is inferred tectonic movement type half-graben previous to the alluvial fan and subsequently the deposition of colluvial facies. In the second time, the occurrence of environmental changes affecting the water regime, accompanied by the change of C3 to C4 vegetation, which in turn causes morphogenetic processes. Simultaneous vegetation change occurs to the alluvial facies. / Leques aluviais são bons indicadores de mudança ambiental e movimento tectônico. Dessa maneira, propõe-se investigar que fatores influenciaram o leque aluvial em desembocadura de canal de 1ª ordem, bacia do Rio Chopim - PR. Para isso, os objetivos foram 1) identificar indícios de neotectônica; 2) caracterizar unidades estratigráficas; 3) identificar processos deposicionais físicos; 4) buscar registros de mudança na vegetação e 5) estabelecer correlação cronológica com eventos globais. Como procedimento metodológico realizou-se: 1) trabalho de campo; 2) trabalho laboratorial e 3) trabalho em gabinete. O trabalho de campo consistiu de: a) estabelecimento da seção estratigráfica HS12, descrições e amostragem dos materiais; b) topografia da bacia de drenagem de 1ª ordem do leque aluvial; c) sondagens eletromagnética e manual sobre o depósito do leque aluvial e d) levantamento estrutural sobre a vertente. O trabalho laboratorial para a seção estratigráfica HS12 na cabeceira do leque aluvial compreendeu: a) análise granulométrica da matriz; b) razão de isótopos estáveis do carbono 13/12 (δ¹³C) e c) datação radiocarbônica (14C). Em relação ao trabalho em gabinete realizou-se atividades como: a) tratamento dos dados granulométricos da matriz pelo Sysgran; b) organização e interpretação das descrições de campo e laboratorial; c) fotointerpretação e d) geoprocessamento. Baseado nos resultados, conclui-se que a evolução do leque aluvial ocorre a partir de 2 momentos principais. Para o primeiro momento, é inferida a ocorrência de movimento tectônico tipo meio-gráben anterior ao leque aluvial e posteriormente a deposição da fácies coluvial. Já no segundo momento, a ocorrência de mudanças ambientais afetando o regime hídrico, sendo acompanhada pela mudança de vegetação C3 para C4 que, por sua vez, provoca processos morfogenéticos. Simultânea a mudança da vegetação ocorre à fácies aluvial.