The aim of this work was to examine the behaviour of sediment, from the perspective of the grain scale mechanics, through computer simulation of grain interactions. A discrete particle model was developed, capable of manipulating the simultaneous motion of large numbers of grains through numerical integration of the equation of motion on an individual basis. Simulations of the critical entrainment shear stress of grains in the surface of single-sized sediment beds demonstrated a distributed nature of threshold values which was dependent upon the arrangement of the randomly deposited bed surface. Geometrical arguments were developed that indicated the existence of general critical entrainment shear stress distributions of both single and mixed-sized beds of a restricted grain size range. Effects of flow sheltering were examined, finding them to hold a significant influence over the effective critical entrainment shear stress distributions. Simulations of saltation trajectories revealed a transition in saltation behaviour associated with a densimetric Froude number, Fr ˜<I> </I>1.2, above which saltation was maintained indefinitely. Trajectory lengths were also investigated over a range of bed grain to saltating grain size ratios and were found to vary linearly with particle Froude number, to a first approximation, for d/D =1. The critical entrainment shear stress and trajectory length results were then incorporated into a probabilistic model which was used to predict fractional bed-load composition, providing valuable insight into the significance of grain scale effects upon large scale phenomena. The results reproduced some of the aspects of the partial transport regime identified by Wilcock (1997), showing evidence of a strong dependency on saltation trajectory length.

Thesis advisor: Noah P. Snyder / River channel morphology in northern New England depends on channel position relative to glacial geomorphology and history. This thesis considers three paraglacial Maine rivers: the West Branch of the Pleasant River (WBPR), a steep inland imposed-form tributary of the Piscataquis River, and the Narraguagus and Sheepscot rivers, two coastal low-gradient rivers. I use a simple model based on the Shields and Manning equations to predict median bed grain size in these recently deglaciated watersheds. The main objectives of this study are to: (1) understand how bedrock controls on the longitudinal profile and sediment inputs impact substrate grain size and channel morphology in the WBPR; (2) apply a model predicting substrate grain size based on digital elevation model (DEM)-derived geometric channel parameters; (3) compare the results from the high gradient WBPR to previously studied low-gradient coastal Maine rivers; and (4) explore the implications of my findings on channel and habitat restoration in paraglacial rivers. I use standard and lidar (light detection and ranging) digital elevation models (DEMs) and spatial analyses to measure channel parameters necessary to predict bed grain size and compare them to field measurements. Predicted bed grain size falls within a factor of two of the field-measured median in ~70% of the study sites. The model performs best in supply-limited alluvial single-thread channel segments with gravel-cobble lag deposit beds, and is less successful in transport-limited depositional segments with relatively fine beds and greater channel variability. Channel segments that are transitional between these two cases (intermediate channel complexity and grain size) are associated with intermediate grain size prediction accuracy. Model failures occur in segments that deviate from the single-thread gravel-bed channel type, and may indicate areas to focus restoration efforts. This study builds on previous research on low-gradient coastal rivers in Maine, and has wide application to future research or restoration projects concerned with sediment mobilization and fluvial ecology. / Thesis (MS) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Only a small body of work currently exists regarding the geomorphology of humid tropical montane rivers. The research that does exist reports rapid geomorphic processes and high sediment loads compared to other montane rivers. This research applies traditional field survey methods combined with new applications of remote sensing techniques to examine the geomorphology and sediment dynamics of the montane portions of the Rio Pacuare in Costa Rica. A suite of geomorphic components (channel slope and width, lateral contributions and planform) are examined and a model presented that illustrates the complexity of the Rio Pacuare’s geomorphology and how the distribution of alluvial sediment varies in relation to geology (tectonics and lithology) and flow hydraulics (stream power). Next, average annual bedload sediment transport capacity is estimated using fifty-one years of daily discharge data at six different locations within the study area, including the temporal (monthly) variability of sediment flux due to dry versus wet season discharge regimes. Then, a time-step hydraulic model is created that simulates observed (modern) and potential future discharge scenarios based on regional climate change model results. The simulated discharge data for two locations within the study area is then integrated into the sediment transport model to examine how sediment flux, and thus channel geomorphology, is likely to change in response to changes in the river’s discharge regime.

Based on case studies in Lao PDR, this research investigates the importance of small waterbody fisheries to rural households, the impact of enhancement initiatives on resources and resource users, and the opportunities and constraints of communityled enhancement. Detailed biological, socio-economic, and institutional data on small water body fisheries were collected and analysed in an integrated framework. Small waterbody fisheries contributed substantially to rural livelihoods, with average household catches of 66 kg/year, equivalent in value to approximately half the household rice production (the major crop grown in the region). Poorer households caught and sold more fish than other socio-economic groups. Active management of small waterbody fisheries by stocking and the regulation of fishing had significant impacts on fish stocks, yields, and the type, magnitude and distribution of benefits to villagers. Stocked fisheries managed by and for the village showed higher standing stocks and returns to fishing effort, and thus generated substantial efficiency benefits even though yields were not significantly higher than in unmanaged fisheries. Benefits were in the form of income to the community, partially passed on to households, (equally between socio-economic groups), through reduced financial contributions to the village. Institutional analysis suggests that locally adapted rules, ownership rights, low cost monitoring and enforcement, and information about benefits are key factors in promoting and sustaining community enhancement efforts, as well as the presence of individuals with substantial leadership skills. Results suggest that communities can and do successfully set up and maintain enhancement initiatives and that enhancement of small water body fisheries can generate substantial benefits. However these will only be sustained if it corresponds to villager's objectives and coincides with conducive institutional arrangements and, crucially, an enabling external policy environment. To achieve the full potential of enhancements, research should be aimed at furthering villager's understanding of the status and potential of their resource in terms of these objectives.

No description available.

The timing and composition of organic matter (OM) inputs to rivers are important as carbon plays a major role in river functioning. Management of Australian rivers since European settlement has altered inputs of organic matter to these systems. Heterotrophic microbes play a critical role in the transformation of OM in rivers, allowing transfer of carbon to other biota. Alteration to the proportions of OM from different sources affects microbial functioning due to differences in OM composition. Macrophytes can represent important sources of carbon to rivers, however their inputs and in-stream processing are poorly understood. The aim of my study was to examine inputs and microbial processing of macrophyte OM in Australian lowland rivers under different flows. Distributions of dominant macrophytes (Typha orientalis, Phragmites australis, Vallisneria gigantea and Persicaria prostrata) were mapped in three lowland river reaches in south eastern Australia. Integration with flow data in a GIS allowed the determination of macrophyte inundation patterns under different flows. Resource allocation (biomass and nutrients), live and dead shoot densities and litter production were monitored in the field over 18 months. DOM release from different macrophyte tissues was examined in the laboratory and leachate composition was assessed using nutrient and spectral analyses. Responses of riverine microbial communities to different OM sources were assessed from substrate-induced respiration and enzyme activity experiments and field measurements of respiration and enzymatic responses to varied OM inputs. Finally, all data were integrated into a model of microbial responses to macrophyte OM inputs induced by different flows. Large populations of macrophytes occurred at all three sites, at bed level, on in-channel benches and on banks. Bank slope, channel heterogeneity and the vertical distribution of macrophyte beds all affected macrophyte inundation patterns. Substantial differences in biomass allocation, nutrient dynamics and litter composition were observed among different plant growth forms and over time. While leaves represented the major shoot component in litter for all species, stems and reproductive structures were also important in some species. Aside from the litter pool, translocation to rhizomes represented a major sink for annual production in emergent plants. Patterns of shoot density and litter production over time varied among species, providing a source of variation for particulate, and hence dissolved OM inputs upon inundation. The majority of DOM release from POM occurred within 24 hours of inundation. Growth form, tissue type (blade, stem, etc.) and status (live or dead) affected rates, quantities and composition of DOM release, with implications for microbial utilisation. Both overall activity and patterns of carbon utilisation in riverine microbes changed in response to altered OM inputs. Patterns of microbial carbon use were shown to be specific to the carbon source which induced them. Modelling showed that flow regulation had a major impact on OM inputs and microbial metabolism, through the effects of flow variability on macrophyte vertical distributions, macrophyte bed inundation and dilution. Positive relationships between discharge, DOM inputs and microbial metabolism were observed at the most highly regulated site (drought < current < historic < flood). While a similar pattern occurred at the less regulated site in terms of total loading, dilution effects resulted in a reversal of this trend on a reach volume basis. Microbial metabolism and DOM inputs were restricted to summer/autumn under regulated flows compared to a greater emphasis on winter/spring inputs and microbial activity under unregulated flows. Continual OM inputs during winter with pulsed inputs in spring under natural flows probably benefit larger, slow-growing macro-invertebrates. River regulation promotes pulsed macrophyte OM inputs during spring/summer, potentially favouring riverine microbial and zooplankton production, although at lower levels due to the overall reduction in OM inputs. The predictive model of macrophyte OM inputs and microbial responses developed throughout this thesis represents a major step forward in our understanding of macrophytemicrobe interactions and our ability to manage our river systems. This work has shown that flow manipulation can be used to influence macrophyte organic matter inputs to rivers and microbial responses, affecting whole stream metabolism and food web interactions.

Thesis (Ph.D.) in Physics--University of Maine, 2006. / Includes vita. Includes bibliographical references (leaves 94-99).

Fundamental to the understanding of how rivers transform and shape our environment is the role of turbulence and complex, three-dimensional flow, such as vorticity, in sediment transport and erosion. However, classical sediment transport models (or formulae) are based, for the most part, on boundary shear stress and do not incorporate these natural phenomena. This is understandable given that the relationship between turbulence generation, intensity and form; the influence of turbulence on mobile sediment; and the magnitude and patterns of deposition and erosion are complex and difficult to quantify. Nevertheless, the failure to incorporate turbulence and complex, three-dimensional flow into existing models means that our understanding of sediment transport remains incomplete. The central hypothesis of this thesis is that vortical motion is the main factor in the development of local scour. To examine this, a comprehensive experimental approach was taken. This approach involved detailed measurements of the unique three-dimensional patterns of velocity, turbulence and bed morphology associated with flow in an open channel with and without the presence of submerged groyne-like structures (stream barbs and wing dikes) at both the laboratory and field scales. Using densely spaced velocity data and new techniques for processing and analyzing these data, it was possible to identify complex features of the flow field at both scales, such as the presence of vortex cores, and correlate these with changes in bed levels. These data provide a unique perspective of the spatial variability of velocity, turbulence and bed morphology in open channels (and in particular in channel bends, where flow is highly three-dimensional). In particular, it was found that, of the flow parameters analyzed, turbulent stresses were most correlated to scour in channel bends without the presence of structures. In contrast, vorticity was found to be the dominant factor in local scour hole development in the vicinity of submerged structures at both the laboratory and field scale. Such data are rare (if non-existent) in existing experimental research, particularly at the scale of a large natural river. This research also examines stream barb design and performance. Stream barbs (also known as submerged groynes or spur dikes) are a relatively novel approach to stream bank protection and are not common in Canada. The design and installation of stream barbs in a creek in Ottawa (Sawmill Creek) was undertaken to serve as a demonstration project for the use of these structures in a semi-alluvial channel, for which no such case studies exist. Three years of monitoring the site and the performance of these structures to reduce bank erosion and improve aquatic habitat have been carried out. Laboratory testing of stream barb performance was also undertaken and showed that with improper design, the outer bank in a channel bend may be more susceptible to erosion due to excessive local scour downstream of the barb. In particular, to avoid bank erosion downstream of the barb, barbs should be small, such that they create minimum flow obstruction, and include a bank key that is wider than the barb itself and extends in the downstream direction.

A hierarchical classification system of Iceland's watersheds and rivers is presented. The classification is based on Iceland's substrate, climate, water, biota, and human cultural influences. The geological formations of Iceland are very different in character depending on their age and formation history. Three major types of formations occur: Tertiary, Plio-Pleistocene, and Pleistocene. These formations have different hydrological characters and different landscapes. There are also large differences in the climate within Iceland. Four major river types are found in Iceland: spring-fed rivers in Pleistocene areas, direct runoff rivers in Plio-Pleistocene areas, direct runoff rivers in Tertiary areas and wetland heath rivers in Tertiary areas. Eleven biogeoclimatic regions occur in Iceland, each having a different watershed type. The classification together with life history theory can explain the distributions, abundances, and life history strategies of Icelandic salmonids. Oceanic conditions must also be considered to explain the life history patterns of anadromous populations. When the freshwater and marine habitat is stable, the life history patterns of individuals in a population tend to be uniform, one life history form being most common. In an unstable environment many life history forms occur and the life span of one generation is long. The properties of the habitat can further explain which life history types are present. In the most stable and favorable rivers of Iceland resident life history forms are more common. Such a classification of a river habitat greatly aids the understanding of the habitat and how it enables and constrains the salmonid populations within it. Consequently adaptations in life histories are better understood and conservation, utilization, and management of these valuable natural resources are made more coherent and efficient. / Graduation date: 1991

Fundamental to the understanding of how rivers transform and shape our environment is the role of turbulence and complex, three-dimensional flow, such as vorticity, in sediment transport and erosion. However, classical sediment transport models (or formulae) are based, for the most part, on boundary shear stress and do not incorporate these natural phenomena. This is understandable given that the relationship between turbulence generation, intensity and form; the influence of turbulence on mobile sediment; and the magnitude and patterns of deposition and erosion are complex and difficult to quantify. Nevertheless, the failure to incorporate turbulence and complex, three-dimensional flow into existing models means that our understanding of sediment transport remains incomplete. The central hypothesis of this thesis is that vortical motion is the main factor in the development of local scour. To examine this, a comprehensive experimental approach was taken. This approach involved detailed measurements of the unique three-dimensional patterns of velocity, turbulence and bed morphology associated with flow in an open channel with and without the presence of submerged groyne-like structures (stream barbs and wing dikes) at both the laboratory and field scales. Using densely spaced velocity data and new techniques for processing and analyzing these data, it was possible to identify complex features of the flow field at both scales, such as the presence of vortex cores, and correlate these with changes in bed levels. These data provide a unique perspective of the spatial variability of velocity, turbulence and bed morphology in open channels (and in particular in channel bends, where flow is highly three-dimensional). In particular, it was found that, of the flow parameters analyzed, turbulent stresses were most correlated to scour in channel bends without the presence of structures. In contrast, vorticity was found to be the dominant factor in local scour hole development in the vicinity of submerged structures at both the laboratory and field scale. Such data are rare (if non-existent) in existing experimental research, particularly at the scale of a large natural river. This research also examines stream barb design and performance. Stream barbs (also known as submerged groynes or spur dikes) are a relatively novel approach to stream bank protection and are not common in Canada. The design and installation of stream barbs in a creek in Ottawa (Sawmill Creek) was undertaken to serve as a demonstration project for the use of these structures in a semi-alluvial channel, for which no such case studies exist. Three years of monitoring the site and the performance of these structures to reduce bank erosion and improve aquatic habitat have been carried out. Laboratory testing of stream barb performance was also undertaken and showed that with improper design, the outer bank in a channel bend may be more susceptible to erosion due to excessive local scour downstream of the barb. In particular, to avoid bank erosion downstream of the barb, barbs should be small, such that they create minimum flow obstruction, and include a bank key that is wider than the barb itself and extends in the downstream direction.