No description available.

The delivery of suspended sediment from drainage basins has frequently been quantified in mass terms by use of the suspended sediment budget approach, which identifies sources, storage and output of mobilised sediment. This thesis investigates the particle size characteristics of the sediment associated with the key components of the suspended sediment budgets of four drainage basins in Devon, U. K. to determine whether particle size selectivity occurs in the delivery of suspended sediment from the hillslopes to the basin outlet. Attention focused on pasture land because previous studies had indicated that this was the dominant source of suspended sediment and that arable fields and channel banks were relatively insignificant in these catchments. Samples of sediment were mobilised from pasture hillslopes using a field-portable rainfall simulator; samples of suspended sediment were collected from the river channel during storm events either manually, by automatic pump samplers or by using rising limb siphon samplers; suspended sediment deposited on the channel bed was sampled using bed traps and by resuspending sediment deposited on the river bed during low flows; and sediment deposited on the floodplain during overbank flooding was collected using Astroturf mat traps or by sampling surface material. Samples were collected to investigate both temporal and spatial variability in grain size behaviour. All sediment samples were pretreated to remove organic matter and their chemically dispersed (absolute) particle size composition was measured using a Coulter LS 130 laser granulometer. The particle size composition of transported/deposited sediment was compared with that of the samples from potential sources to determine whether particle size selectivity had occurred. Where possible, measurements of the natural in situ particle size distribution (effective particle size) were also undertaken by quick return of samples to the laboratory for immediate measurement without pre-treatment using the laser granulometer. Particle size selectivity was found to have occurred in the mobilisation of sediment from the hillslope pasture land sources. Seasonal variations were identified in the particle size characteristics of both sediment mobilised from the hillslopes and suspended sediment samples. Spatial variations were identified in the particle size composition of sediment deposited on the floodplain. These seasonal and spatial variations reflect the particle size selectivity of detachment, transport and deposition processes which is in turn influenced by the aggregation or flocculation (effective particle size) of the sediment.

Thesis (M.S. - Geosciences) - University of Arizona. / Includes bibliographical references (leaves 125-130).

Thesis (M.Env.St.)--University of Adelaide, Dept. Geographical and Environmental Studies, 1999. / Bibliography: leaves 110-115.

Thesis (M. P. A.)--Texas State University-San Marcos, 2009. / "Spring 2009." Includes bibliographical references (leaves 94-99).

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [256]-272).

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (May 1, 2007) Vita. Includes bibliographical references.

No description available.

Evaluating and educating communities on their flood risks is an integral part of adapting to climate change and more extreme precipitation patterns. Low-income communities are often the most affected by in-land floods. They are more likely to live in floodplains and have less socioeconomic mobility. This thesis takes a two-pronged approach to evaluating flood risk. First, a flood risk model that identifies areas of high runoff in Giles County, Virginia was developed. The model accounts for land cover, soil type and elevation. The soil retention layer and Digital Elevation Model (DEM) produced a cell by cell layer of runoff. Storm data was collected from the NEXRAD program and integrated into the runoff layer. Countywide maps of low, moderate and high risk were produced. Semi structured interviews were then conducted to gauge the usability of the maps within high risk areas. Interview feedback was transcribed and coded for analysis. Themes identified throughout the interviews, were used to make adjustments to the model and maps. This experience suggests that combining technical analysis and community engagement can create a more accurate depiction of flood risk that is meaningful to those most affected. This paper also suggests that evaluating riverine flooding based on the most severe, recent storm yields a more accurate and impactful tool than previous flood modeling methods. This work takes flood modeling a step farther by receiving community input and shows that models are only as useful as they are meaningful to the most impacted communities. / Master of Urban and Regional Planning / Climate change models suggest that many communities will experience fewer precipitation events, but when precipitation events do occur they will be more intense and thus destructive. Communities can expect a higher risk of flooding, which is why it is important to plan proactively and understand where the most at-risk areas are. To help Giles County, VA understand its flood risk we created a tool that displays storm runoff. Elevation, soil type and vegetation were incorporated into the model. Storm data was integrated into the model and compared to annual precipitation levels. Countywide maps of low, moderate and high risk were produced. In order for the maps to have the maximum impact they need to be accessible to at risk populations. To gauge the accessibility of the maps to the community semi structured interviews were conducted within the high risk areas. Issues and opportunities identified through the interviews were used to make adjustments to the model and maps. The findings suggest that combining technical analysis and community engagement can create more accurate depictions of flood risks that are meaningful to those most affected. Future research efforts should include incorporating anticipated development schemes into the model and hosting more in depth community engagement activities. The importance of community engagement is highlighted in this research, as the interviews has a major impact on the outcome of the model.

Sediment and microplastic accumulation in stream systems occur when particulates entrained in overbank flow are retained by the floodplain. Despite overbank flow conditions dictating sediment and microplastic accumulation, the spatial distribution of accumulation within floodplains remains poorly understood. Difficulty quantifying hydraulic flow conditions is due to spatial variation introducing erroneous error. This study hypothesized floodplain sediment and microplastic accumulation would be closely correlated with topographic, vegetative, and hydraulic conditions. To test this hypothesis, sediment and microplastic accumulation were measured along a 1.25 km stretch of Stroubles Creek in Blacksburg, Virginia. Sediment accumulation was measured using tiles with a surface area of 144cm² at 75 locations. Tiles accumulated 4,782g over their two-year deployment. Microplastic accumulation was assessed by taking 15cm3 soil grab samples from 40 locations. Microplastics were identified using FTIR spectroscopy and were found to have a concentration of approximately 7MPm-3. Topographic and vegetative variables were measured using digital elevation and canopy height models, while hydraulic variables were calculated with an unsteady flow model in HEC-RAS. Sediment and microplastic accumulation were both found to be significantly influenced by terrain and hydraulic conditions. Sediment accumulation yielded an MLR model with an R2 of 0.72, with a confidence level between 97% - 99%, while the microplastic model yielded an R2 of 0.26 and with a confidence level between 95% - 98%. Differences in sediment and microplastics particle density resulted in hydraulic conditions being more influential on microplastic accumulation with an R2 81.5% greater than any its terrain components. This research identified floodplain accumulation process drivers which could help to guide future management decisions regarding sediment storage and monitoring microplastic accumulation. / Master of Science / Streams act as natural thoroughfares, with the potential to transport materials beneficial and harmful to biological and environmental processes. During flood events, the material carried by stream flow is often deposited in areas adjacent to the main channel. These adjacent areas are called floodplains and contribute to the accumulation of sediment and small pieces of plastic in stream systems. Spatial patterns in floodplain accumulation are believed to be the result of site-specific terrain, vegetation, and flow conditions within a stream system. In the context of a stream system, descriptive characteristics of terrain, vegetation, and flow conditions are heavily confounded making their relationship with floodplain accumulation difficult to interoperate. This study aims to understand the accumulation of sediment and plastics in the Stroubles Creek floodplain by evaluating the terrain, vegetative, and flow conditions believed to influence systematic patterns in accumulation. Floodplain sediment and plastic accumulation were measured along a 2 km reach of Stroubles Creek at 75 and 40 sampling locations. Terrain, vegetative, and flow conditions at each of the sediment (75) and plastic (40) sampling locations were determined to be the characteristics driving their relative accumulation process. The distance and change in elevation of the sampling locations from the channel, flow velocity of water, arrival time and duration of time each location experienced floodwaters were observed to have the most significant impact on accumulation processes. However, the degree to which each of these variables affected sediment and plastic accumulation differed. These findings suggest that sediment and plastic accumulation are both heavily influenced by terrain and flow conditions; however, the processes by which sediment and microplastics accumulate in the floodplain are likely to differ.