Rozprawy doktorskie na temat „Debris morphology”

Those who frequent the coastline may be accustomed to seeing driftwood washed onshore, some of it having seemingly found a home there for many years, others having been freshly deposited during the last set of storms; However, if a passerby were to take a closer look at the driftwood on the coastline, they may notice that some of these logs – also known as Large Woody Debris (LWD) – are anchored in place, a practice which is generally used for the purpose of stabilizing the shoreline or reducing wave-induced flooding. Records of existing anchored LWD project sites date back to 1997 and anecdotal evidence suggests that the technique has been used since the mid-1900’s in coastal British Columbia (BC), Canada, and Washington State, USA. Now, with an increased demand for natural and nature-based solutions, the technique is again gaining popularity. Despite this, the design of anchored LWD has largely been based on anecdotal observations and experience, as well as a continuity of design practices from the river engineering field. To date, there is no known peer-reviewed literature on the design or efficacy of LWD protection systems in a coastal environment. In 2019, the “Efficacy and Design of Coastal Protection using Large Woody Debris” research project was initiated to determine if LWD are effective at stabilizing the shoreline under wave action, if they are effective at reducing wave run-up, and if they are durable enough to meet engineering requirements for shore protection. In addition, the project aimed to determine the optimum configuration of LWD for design purposes. To meet these objectives, this study included the following work: (1) field studies of existing LWD installations, (2) experimental modeling of beach morphology with and without LWD structures, (3) experimental modeling of wave run-up with and without LWD structures, and (4) development of preliminary design guidance. The first phase of the project included field investigations at 15 existing anchored LWD sites in coastal BC and Washington State. Site characteristics, design techniques, and durability indicators were examined and correlated to a new design life parameter: ‘Effective Life’. Six primary installation techniques were observed: Single, Multiple, Benched, Stacked, Matrix, and Groyne. Observed durability and/or performance issues included: missing LWD, erosion, arson, wood decay, and anchor corrosion/damage. The Effective Life of anchored LWD was found to be strongly correlated to the tidal range and the upper beach slope for all installation types, and the LWD placement elevation relative to the beach crest elevation for single, shore-parallel structures. The many noted durability issues and ineffectiveness as mitigating erosion indicates that existing design methods for anchored LWD have not generally been effective at providing coastal protection and meeting engineering design life requirements. A comprehensive set of over 60 experimental tests were completed as part of the overall research program. Thirty-two (32) tests were analyzed as part of this study relating to the morphological response of a gravel beach with and without various LWD configurations. The tests were conducted within a wave flume at the National Research Council’s Ocean, Coastal and River Engineering Research Centre (NRC-OCRE), at a large scale (5:1) based on site characteristics and LWD design characteristics made during the previous field investigations. Tests were also conducted to assess experiment repeatability, sensitivity to test duration, sensitivity to wave height, wave period, and relative water level, influence of regular waves, and influence of log roughness. The position of the most seaward LWD (whether considering distance or elevation) was found to be strongly linked to morphological response. A theoretical relationship was developed between LWD elevation and sediment volume change. Configurations which included LWD placement below the still water level, such as the Benched configuration, were found to be most effective at stabilizing the beach profile. As part of the experimental modeling program, 24 tests were also conducted for the purpose of estimating the effect of LWD design configuration on wave run-up. In total, six different beach and LWD configurations were tested under a base set of four regular wave conditions. The study findings indicated that anchored LWD may increase wave run-up relative to a gravel beach with no structures. In particular, configurations with more logs tended to result in higher wave run-up. However, additional research is needed on the effect of LWD on wave run-up to confirm and expand these findings. There are a number of potential engineering, ecological, social, and economic benefits associated with anchored LWD installations if designed, installed, and monitored appropriately for the site conditions and user needs. To realize these potential benefits, significant additional research is needed on the topic. One of the most significant barriers to usage is a lack of information on how to effectively anchor LWD structures. However, this research project provides a baseline for future comprehensive studies on the effect and design of coastal protection using LWD. The project provides preliminary design considerations for the usage of LWD as coastal protection and contributes to the growing body of literature on nature-based solutions.

Reaches dominated by debris flow scour and incision tend to greatly influence landscape form in steepland basins. Debris flow networks, despite their ubiquity, have not been exploited to develop erosion rate proxies. To bridge this gap, I applied a proposed empirical function that describes the variation of valley slope with drainage area in fluvial and debris flow reaches of steepland channel networks in the Oregon Coast Range. I calibrated a relationship between profile concavity and erosion rate to map spatial patterns of long-term uplift rates assuming steady state. I also estimated the magnitude and inland extent of coseismic subsidence in my study area. My estimates agree with field measurements in the same area along the Cascadia margin, indicating that debris flow valley profiles can be used to make interpretations from spatial patterns of rock uplift that may better constrain physical models of crustal deformation. This thesis includes unpublished co-authored material.

Research on hillslope surface processes and hillslope stratigraphy has been neglected in southern Africa. The amount of published literature on hillslope stratigraphy in southern Africa is very limited. Hillslope sediments provide a record of past environmental conditions and may be especially useful in calculating the recurrence interval of extreme environmental conditions such as earthquakes and intense rainfall events. The characteristics of hillslope sediments provide information as to their origin, transport and mechanisms of deposition. No published work could be found that had been undertaken on hillslope surface processes or stratigraphy in the eastern Cape coastal region. This study attempted to fill this gap in the geomorphic literature for southern Africa. The surface processes acting on hillslopes at Burchleigh and Spring Grove in the Alexandria district of the eastern Cape were examined in terms of slope morphology, surface sediment characteristics and the internal geometry of the hillslope sedimentary deposits. The late Quaternary hillslope sedimentary deposits at the two study sites are composed of fine grained colluvial sediments intercalated with highly lenticular diamicts. The fine grained colluvial sediments were emplaced by overland flow processes while the diamicts were deposited by debris flows. The sedimentary sequences at both study sites have a basal conglomerate interpreted as a channel lag deposit. Most slope failures preceding debris flow events were probably triggered by intense or extended periods of rainfall associated with cold fronts or cut-of flows. Seismic events may also have triggered slope failure, with or without the hillslope sediments being saturated. The results of this study indicate that a continuum exists between the slopewash dominated processes of the presently summer rainfall regions of Natal to the present winter rainfall regions of the western Cape where mass movement processes are significant. Hillslope deposits, therefore, provide a record of environmental conditions which may greatly facilitate proper management of the landscape.

In Kentucky, Best Management Practices (BMPs) were developed to protect the integrity of water resources during and after silvicultural operations, but their effectiveness is largely unknown. The study objectives were to (1) quantify the extent to which current BMPs minimized logging-related changes in stream water quality, channel morphology, and the content of woody debris and (2) quantify the extent to which modified BMPs influenced these characteristics. Six watersheds in eastern Kentucky were commercially logged in 2008-2009. In each watershed, one of three treatments was implemented (each replicated once). Treatment 1 (BMP) was based on current Kentucky BMPs. In treatments 2 (BMP+) and 3 (BMP++), current BMPs were modified with additional protective measures. Before the harvest, sampling sites were established in each watershed. Channel morphology and woody debris data were collected at each site in 2006 and again 2014. Data for water chemistry were retrieved from ongoing sampling records. BMP watersheds were compared to one another and to unharvested control watersheds in each year independently. Data within each individual watershed were also compared across years. The results indicate that current BMPs were effective in minimizing changes in the watershed characteristics examined here, and the benefits of modified BMPs were highly variable.

Natural wood in rivers has received wider attention in the scientific community only over the past two decades from different perspectives (biological, geomorphological and engineering). Wood has been studied mostly in mountain basins whereas large rivers have been less investigated. The present research deals with different aspects related to in-channel wood in gravel bed rivers, including physical wood characteristics, wood storage and transport, and link between wood abundance and river morphology. The analysis of physical characteristics of wood was carried out in three rivers: the Piave River (Veneto, Italy), the Magra River (Toscana, Italy) and the Ain River (Rhône- Alpe, France). Different variables were compared for a specific species (Populus nigra). Mean wood density range from 0.25 to 0.35 g/cm3, with Ain’s values differing significantly from the other rivers. The age of sampled wood elements is similar in the Piave and in the Magra (16 and 17 yr, respectively), whereas Ain’s samples are much older (31 yr). The growth coefficient si instead similar for the three rivers, but resistance to penetration is significantly higher in the Piave and presents a positive correlation with sample’s age. As to wood transport, 10 logs were tagged with metal tags and radiofrequency transmitters to monitor their mobility. Unfortunately, the 2005 fall season was very dry and no significant events occurred, also the 2006 spring snowmelt runoff did not reach a sufficient stage to mobilize the tagged logs. In September 2006, the largest event of the year (below bankfull stage) did not reach the logs, but the bar erosion taking place near one tagged log caused its recruitment into the flow and its transport downstream. Transport distance was about 4 km, i.e. about 18 times the mean channel width. The wood storage survey has regarded a 30 km reach in the Piave river between Ponte nelle Alpi and Busche (Belluno). Here the rivers features braided and wandering morphologies. Two integrated methods were implemented: field measurements in selected plots and interpretation of high-resolution (10 cm pixel) aerial photos at the reach scale.. Errors associated to wood measurements by using aerial photographs were evaluated the field plots. Results are encouraging, showing a good potential and efficiency of such approach for rivers where a total field survey would be unfeasible (ED < 50% per D < 15 cm; 40 < ED < 50% per 15 cm < D < 20 cm; ED < 10% per D > 20 cm). The analysis based on aerial photos led to estimate average wood load to be within the range 3.7 – 9.1 m3/ha, depending on how wood jam volume is computed. Single wood elements present a mean diameter of 28 cm and a mean length of 7.5 m. Tree species indicate most of the wood derives from the riparian corridor but other species are also present due to lateral erosion of recent low terraces. The analysis of wood storage at different reaches showed that wood is more abundant in braided channel more than in wandering reaches. Wood is mostly located on bars (rather equally in high and low ones), but a considerable fraction of wood is associated to islands in the wider braided reaches. A strong negative correlation is present between single wood elements’ volume and relative area occupied by low flow channels, whereas wood jam volume is strongly correlated with the relative area of islands.

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Trees, twigs and leaves fallen inside of the channel, form a significant component of the fluvial environment and natural occurrence in fluvial systems that cut forested areas. All these vegetal materials that are found inside of the channel are called wood debris. The wood debris play a key function in the ecology and geomorphology of channels, being able to affect the processes of the channels in an ample reach: since the hydraulic roughness, retention and sized grain of bed sediments, until the creation of steps and pools, being able to the times to control the standard of the channel and distance and/variation of fluvial features that are basic for the formation of aquatic habitat. In this context, the present research had as objective, to verify the influence of accumulations of wood debris on the morphology and sedimentology of stream bed in the river Guabiroba, Guarapuava, Center-South of the Paraná. The used techniques had included: installation of permanent transversal profiles (to the upstream and downstream of the accumulations) and sections of batimetric measurement, survey of the longitudinal profile and grain sized characterization of bed sediments. The measurement was carried throughout 15 months (December of 2007 the March of 2009) in four sections located in the main course of the river. The rainfall during the measurement allowed to particularizing the occurrence of only one period with rains above average (3 - 4ª Campaign). The results indicate the occurrence of sedimentation in the second and fifth measurement and processes of erosion in the third and fourth measurement. These processes erosive-depositional can in part be attributed to the pluviometric regime, with the periods of high entailed concentration of rains to the erosion of the stream bed and periods of related scarce and not concentrated rains with the deposition of sediments. The analysis of the data allows to establish some consideration: 1) predominance of processes of erosion in the sections of batimetric measurement; 2) bigger rate deposition in downstream cross-sectional profiles of the accumulations; 3) predominance of coarser sediments (gravel medium - sand very coarse) to upstream and finer sediments (gravel fine - sand medium) to downstream; 4) bigger diversity of depths in the immediacy of the accumulations; 5) establishment of riffles by the forced deposition of sediments and pools for the scour of the stream bed.
Árvores, galhos e folhas caídos dentro do canal formam um significativo componente do ambiente fluvial e de ocorrência natural em sistemas fluviais que cortam áreas florestadas. Toda essa carga de material de origem vegetal que se encontra dentro do canal é chamada de detritos lenhosos. Os detritos lenhosos desempenham função chave na ecologia e geomorfologia de canais, podendo afetar os processos do canal em um amplo alcance: desde a rugosidade hidráulica, retenção e grânulometria dos sedimentos de leito, até a criação de degraus e depressões, podendo, às vezes, controlar o padrão do canal e a distância/variação de feições fluviais que são fundamentais para a formação de habitat aquáticos. Num contexto desses, a presente pesquisa teve como objetivo verificar a influência de acumulações de detritos lenhosos sobre a morfologia e a sedimentologia de leito no Rio Guabiroba, município de Guarapuava, mesorregião Centro-Sul do Paraná. As técnicas utilizadas incluíram: instalação de perfis transversais permanentes (a montante e a jusante das acumulações) e seções de monitoramento batimétrico, levantamento do perfil longitudinal e caracterização grânulométrica de sedimentos do fundo. O monitoramento foi realizado ao longo de 15 meses (dezembro de 2007 a março de 2009) em quatro pontos localizados em dois trechos no curso principal do rio. A pluviosidade durante o monitoramento permitiu individualizar a ocorrência de apenas um período com chuvas acima da média (3ª a 4ª campanha). Os resultados indicam a ocorrência de sedimentação na segunda e quinta campanhas e processos de erosão na terceira e quarta campanhas. Esses processos erosivo-deposicionais podem, em parte, ser atribuídos ao regime pluviométrico, com os períodos de alta concentração de chuvas vinculados à erosão do leito e períodos de chuvas escassas e não concentradas relacionados com a deposição de sedimentos. A análise dos dados permite estabelecer algumas considerações: 1) predominância de processos de erosão nas seções de monitoramento batimétrico (Blocos 3D); 2) maior taxa de deposição nos perfis transversais situados a jusante das acumulações; 3) predomínio de sedimentos mais grossos (seixo médio - areia muito grossa) a montante da acumulação do que a jusante (seixo fino - areia média); 4) maior diversidade de profundidades nas imediações das acumulações; 5) estabelecimento de soleiras pela deposição forçada de sedimentos e depressões pela escavação do leito.

L'etude locale du charriage torrentiel sur modele reduit de tres faible taille a montre que deux phenomenes nettement distincts cohabitent. D'une part, le charriage hyperconcentre correspond a un controle du transport solide et du lit par les conditions hydrauliques, le debit solide est tres importants et les grains sont d'autant plus facilement transportes qu'ils ont gros. D'autre part, lors du charriage ordinaire, la fourniture de materiaux par le lit est preponderante, les elements fins sont les plus mobiles et le debit solide varie dans des proportions importantes pour des conditions hydrauliques identiques. Il y a basculement irreversible d'un phenomene a l'autre. L'utilisation d'un modele de grande taille a montre que cette dualite se traduit par une heterogeneite spatiale des phenomenes, le tri granulometrique favorisant le deplacement des elements de taille moyenne. La confrontation de ces resultats a des observations de terrain a degage des regles de fonctionnement des torrents reels et a permis d'affiner la lecture morphologique et les mesures granulometriques du lit, facilitant alors considerablement l'approche des phenomenes torrentiels dans le cadre des etudes de cas

Les effondrements de flanc déclenchent de larges avalanches de débris et glissements de terrain, provoquant ainsi une modification de la pente du volcan et altérant le paysage. Les différents types de volcans subissent des effondrements de flanc lors de leur développement. Aux Philippines, par exemple, les volcans présentant des brèches sont les cônes, sub-cônes et volcans massifs. Les avalanches de débris affectent les édifices volcaniques et non-volcaniques ; leur étude constitue donc un enjeu primordial pour l'évaluation des risques naturels. Les dépôts d'avalanche de débris (DAD) présentent des structures de surface et internes, des morphologies et des textures pouvant être utilisées pour déterminer le type de transport, les mécanismes de déformation et les vitesses d'emplacement de l'avalanche de débris. Cependant, sur le terrain, les DAD sont souvent vastes et chaotiques, ainsi l'apport de la télédétection complète l'étude de terrain en apportant une vision d'ensemble de l'avalanche. Notre étude s'intéresse à la structure et morphologie des DAD par l'utilisation de modèles analogiques et en contexte naturel via l'étude du Mt Iriga et Guinsaugon aux Philippines et à travers d'autres sites dans le monde (Mt Meager, Canada ; Storegga Slide, Norvège). L'étude de la vitesse de mise en place, de la dynamique et des mécanismes de déformation des avalanches de débris s'est faite via la modélisation analogique. Il apparait ainsi que la formation de "hummocks" est un processus clé dans la structuration des DAD. Les "hummocks" sont des parties massives du volcan arrachées lors de l'avalanche de débris et qui se disloquent au fur et à mesure de son avancée. Cette dislocation des "hummocks" s'effectue via l'apparition de failles normales à fort pendage qui fusionnent avec les zones de cisaillement à faible pendage situées à la base du glissement. Les "hummocks" fournissent des informations sur les conditions de transport et la composition initiale de l'avalanche. Leur géométrie (taille et forme), leur structure interne et leur distribution spatiale sont des indicateurs de la vitesse du développement de l'avalanche. Ils permettent d'interpréter sa dynamique de mise en place. Les expériences analogiques utilisant une rampe courbée montrent le développement de zones d'accumulation et d'épaississement à l'endroit où les matériaux atteignent une surface de dépôt à faible pente. Les expériences avec des rampes rectilignes montrent de plus long glissement. L'extension de ces avalanches est accommodée par des structures en horst et graben ainsi qu'en transtension. Le dépôt consécutif à l'avalanche peut ê remobilisé lors d'effondrements secondaires. L'ensemble de ces expériences montre que la morphologie de la surface de glissement influence les mécanismes de mise en place, l'extension spatiale et la structure de l'avalanche. La cartographie structurale et morphologique acquise par télédétection ainsi que la description de caractéristiques récurrentes sur plusieurs DAD, difficiles d'accès et jusqu'ici non cartographiés (Süphan Dağı (Turkey), Cerro Pular-Pajonales (Argentina), and Tacna (Peru), a permis de préciser les scénarios, les causes et les facteurs de mise en place des DAD. La cartographie des DAD est une étape nécessaire pour retracer les évènements passés et estimer les risques naturels dans une zone spécifique. L'identification et la description des morphologies et structures des DAD devraient permettre la compréhension des mécanismes de mise en place de l'avalanche.

碩士
國立臺灣大學
土木工程學研究所
102
The aim of this thesis is to investigate the morphology of debris fan by conduct a field survey in Pu-Tun-Pu-Nas River debris fan of Laonong River and experiment observation with the Photogrammetry survey method. Aerial UAV Photogrammetry survey with ground controlled marker target can bring high quality digital surface model in a parity cost. Designed mirror array build in laboratory can provide stereo images for reconstruct experiment debris fan topography. Two experiment conditions are adopted to simulate fluvial fan and mudflow formed composition pattern. These two formation pattern might be possible in the field according to the comparison result between field and experiment. The result of experiment shows these two experiments might reach a dynamic equilibrium elevation in late stage from an initial stage of elevation growth.

碩士
國立中興大學
水土保持學系所
97
The typhoons induce disasters of landslides and debris flow, bringing amount of large woody debris (LWD) which blocked the river and affected the flood expellant, and water supply in Taiwan. According to above results, the government has focused on the problem of LWD seriously. There are three main functions for LWD in a river: (1) To intercept the sediment on the river bed. (2) To block and separate the water flow. (3) To stabilize the river bank and lessen the scour. Above all, this experiment conducts the scour depth and sediment export of channel river bed with or without LWD in the channel. We explore the river patterns of the inter-relationship with the LWD, and analyse the LWD’s deposition pattern and speed in different channels. Results indicate that LWD within the channel not only block and separate the flow effectively, but also change the river morphology. Because LWD which reduse the water flow could lessen the scour on river bed, and induse the bars formed of LWDs downstream side. LWD jam was accumulated by LWDs. Pools and Bars are formed in the LWD jam’s upstream and downstream. It could provide habitats for aquatic organisms, and increase the overall biodiversity of the river. In the deposition patterns, LWD parallel to the water has the highest percentage, followed by oblique, and finally for the perpendicular. When the ratio of channel width and LWD length is less than 0.5, the longer the higher proportion of the deposition of the LWD is parallel to water. When the ratio is greater than 0.5, the LWD is easier to deposit perpendicular to the flow. The size of the LWD diameter to the deposition pattern has no significant relationship. Moving speed is inversely proportional with the LWD lenth; the size of the LWD diameter to the moving speed has no significant relationship. LWD jam will be more effective in blocking the LWD from the upstream, and reduce the moving speed of LWD. And LWD could stably deposit in oblique or perpendicular to flow when LWD were accumulated.

碩士
國立臺灣大學
土木工程學研究所
99
The aim of this thesis is to understand the relationship between rheology and morphology for debris flow going from a narrow valley to a fan. In micro-scale experiments, Kaolinite, black sand and water are mixed to represent debris flows of high viscosity. We change two parameters which are water content and the coarse particle content to observe variation in debris flow behavior due to changes in composition. To measure the fast flow and rapid deformation of the flow surface, a fast scan method using a high speed camera and rotating laser are developed. The results of the experiments are analyzed in two parts, one is channel flow behavior and another is the canyon-fan transition. In channelized results beside compare the experiments, we use kinematic wave to simulate the surge process in channel, and compare the cross section in field. At the canyon-fan transition, debris flow deposit in two stages. In the first stage, a high speed front advance on to fan. In the second stage, the slower tail tends to spread laterally. Increasing water content and decreasing coarse particle content makes the first stage longer and the second stage shorter. As a result, lateral deposits are few pronounced. Finally, the experimental results are compared with field observations.

碩士
逢甲大學
水利工程所
93
Even the flow deflector structures are useful on controlling channel banks erosion, the safety and its stability of the non-concrete deflector constructed by natural materials are still the major concerns for engineers and residents in Taiwan. Focused on the single flow deflector made of woody debris, this study tries to find the better structure configuration for considering the needs in structure safety, erosion control, and habitat enhancement through model experiments on concrete groyne, deflector log, and large woody debris. The flume experiments are undertaken with different experiment conditions of flow discharge, sediment composition, and channel slope. The experimental results indicated that the large woody debris is good at bulwark ability, channel steady and variety of habitat enhancement. The deflector log has good ability of variety of habitat enhancement in low flow discharge. As flow discharge increases, the concrete groyne and large woody debris perform better in variety of habitat enhancement and diversity. In structure safety, the concrete groyne and large woody debris are the better structures in bulwark ability while the flow energy increases. For these three structures, the large woody debris is the best structure in safety and habitat enhancement, while deflector log is concluded as the worst one.

This thesis looks at the comparison between grain micromorphology of moraines, debris flows and similar accumulations. Moraine samples were taken in the Černé jezero Lake area, Bohemian Forest, in the Velická dolina Valley, High Tatras, and in the Labský důl Valley, Krkonoše Mts. Samples of debris flows and unverified accumulations were taken in the Důl Bílého Labe Valley, Krkonoše Mts., and further samples of accumulations were obtained from the valley of Prudký potok Stream, Králický Sněžník Mts., the valley of Vražedný potok Stream and Velká Kotlina, Hrubý Jeseník Mts. Sediments were examined under electron microscope and their morphological characteristics and influence of the environment were identified and described. Calculated exoscopic moraine standard was used for comparison of examined forms of relief using distance coefficients, statistical analysis were carried out which identified diagnostic characters for distinguishing moraines and debris flows. There was also calculated exoscopic standard for different types of moraines (frontal, lateral, basal). This research highlighted the differences between moraines and debris flows, and between different types of moraines. The study also proved that typical glacial microtextures, that are generally accepted, occur at similar levels on grains...