Quantitative evidence supplied by bottom sediment textural analysis, Fourier grain-shape analysis and Q-mode factor analysis indicate that river-borne sand-sized sediment originating in the upper reaches of the Rappahannock is actively transported downstream and ultimately delivered to the estuarine sediment regime. Current velocity observations in the upper estuary as well as suspended sediment concentrations measured at stream gaging stations, indicate that short-term extreme hydrological events such as periodic river flooding provide a plausible transport mechanism to move river-borne sands into the estuarine sediment regime.Events of this nature can disrupt average partly-mixed estuarine circulation patterns by displacing the salt-wedge to a more seaward position, increase stratification and create a net-seaward river-type flow within the affected portions of the estuary; thus, allowing high concentrations of river-borne sediments associated with the high freshwater inflow to move into the estuary and become incorporated into the estuarine sediment regime. Bottom sediment textural analysis indicates that the two major landward sources of sand-sized sediment to the Rappahannock Estuary are the Piedmont-derived river sands and sand-sized sediment derived from the constant denudation of fastland bluff sediments which directly outcrop along certain reaches of the Rappahannock River. Sand-sized sediment is consistently present within all the bottom sediment samples taken from the estuary channel as well as along its flanking shoals. Fourier grain-shape analysis serves to differentiate the Piedmont-derived river sands from the fastland bluff sands in that the sand-sized sediment derived from each of these provenances possess highly contrastable shape attributes. Based upon the distribution of Fourier harmonic amplitudes of ninety-four sand-shape samples over a defined range Fourier harmonic amplitude class intervals, it is found that the river sands and fastland bluff sands represent two statistically non-similar sand-shape populations. The distribution of Fourier harmonic amplitudes also suggests that these two non-similar sand-shape populations mix together within the river's active transport system landward of the Rappahannock Estuary. The proportional mixing of these two sand-shape populations and subsequent downriver transport results in the delivery of both shape populations into the estuarine sediment regime where they may become deposited and/or redistributed within the estuarine sediments. Q-mode factor analy��is is employed in order to determine the relative extent of the proportional mixing of the two non-similar sand-shape populations within the active transport system of the Rappahannock River-Estuary via the grain-shape information supplied by Fourier analysis. Q��mode analysis determined that three compositionally distinct end-members, or factor components, are sufficient enough to encompass 98.5% of the total grain-shape variance contained within the distribution of Fourier harmonic amplitudes for the ninetyfour sand-shape samples. Based upon the distribution these samples within the defined factor (variable) space, it is quantitatively determined that various percentages of the Piedmont-derived river sands are present within the bottom sediments of the Rappahannock Estuary both in the estuary channel as well as along its flanking shoal areas. Thus, Fourier grain-shape analysis proves as a useful geological tool in that it quantitatively determines that river-borne sand-sized sediment is present within the Rappahannock estuarine sediment regime.

No description available.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 36-41). Also available on the World Wide Web.

As the population on the island of Maui drastically increases, water resource demands continue to rise. In order to match water demands and to manage water resources, it is important to understand streamflow and drainage basin interactions. If relationships between a drainage basin’s hydrologic and geomorphologic characteristics can be quantified, then streamflow conditions of ungaged streams can potentially be estimated. The baseflow recession constant is an important variable to analyze for water management, yet until this study, recession constants were not calculated for the island of Maui, or Hawai‘i as a whole. Recession constants of currently gaged streams on Maui correlated to the permeability and flow conditions of the watersheds. Streams with recession constants >0.95 were generally placed in areas of the island with dike-impounded groundwater and streams with recession constants

M.Sc., Faculty of Science, University of the Witwatersrand, 2011 / Prolonged snow cover in Lesotho frequently results in human and livestock deaths, due to isolation and exposure. MODIS Rapid Response imagery is emerging as an important source of near real-time data for global hazard mapping and emergency response. A dataset of daily MODIS snow cover images for the period 2003 – 2010 was acquired for Lesotho. Combined with high-resolution SPOT satellite images for two study areas, MODIS snow cover images were used to establish the frequency, extent and timing of snowfalls. A digital elevation model was used in conjunction with mean air temperature data to investigate the effects of altitude, aspect and temperature on the mean rate of daily snowmelt. A strong correlation exists between mean day-time temperatures and the mean rate of daily snowmelt throughout the winter season. The mean rate of snow dissipation is most rapid after late season (September – November) snowfalls and least rapid after mid season (July – August) snowfalls. Snow cover persisting for 1 – 5 days dissipates at a higher mean rate than snow cover that has persisted for 6 – 10 days. Snow lasts longest on south-facing slopes above 2500m a.s.l, with evidence of increased ablation due to wind deflation and higher insolation levels in the highlands above 3400m a.s.l. The southern Drakensberg highlands in the district of Quthing have the highest mean duration of snow cover (21 – 25 days per annum). The seasonal extent and duration of snow cover was related to the spatial location of villages and roads in Lesotho, in order to determine individual vulnerability to negative impacts associated with prolonged snow cover. A ranking system was applied to each village according to the seasonal duration of snow cover, and the accessibility and proximity to the nearest road. Snowfalls occur between 1 and 8 times per annum on average. Therefore, village vulnerability is generally low, as most settlements are situated on predominantly north-facing slopes in the western lowlands and Senqu River Valley, which remain largely snow-free throughout the winter season. Few villages experience prolonged snow cover, which is limited to predominantly south-facing slopes above 2500m a.s.l along the escarpment and interior mountain ranges. Village vulnerability increases during the mid season period as a result of the increased frequency and duration of snow cover in July and August. The villages of Thoteng (Butha-Buthe), Letseng-la-Terae (Mokhotlong) and Mabalane (Butha-Buthe) have the highest vulnerability for the 2003 – 2010 period.

No description available.

Thesis (B.A.Hons.) from the Department of Geography, University of Adelaide, 1977. / Includes bibliographical references (p. i-iii).

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 221-224).

Doctor of Philosophy / Department of Geography / Charles W. Martin / Disturbance regimes are important determinants of both terrestrial and aquatic ecosystem structure and function. Disturbances may linger in the landscape and lag temporally, influencing stream ecosystem form and function for decades, if not centuries. The recent enhanced Mountain Pine Beetle (MPB) infestation in pine forests of the Rocky Mountain region has resulted in extensive tree mortality, producing the potential for significant increases in carbon supply to stream channels. To better understand MPB impacts on in-stream large wood (LW), a census was conducted in 30 headwater streams within the Medicine Bow National Forest in south-central Wyoming, across the temporal spectrum from early- to late-stage MPB-infestation. A subset of those streams exhibiting mean conditions at each level of infestation was surveyed to determine any significant differences in channel morphology or aquatic ecosystem function. Results indicate that wood loads related to the MPB-infestation significantly increase with time since initial infestation. However, even in late-stage infestation streams, many of the fallen MPB-killed trees are bridging across the channels and have yet to break and ramp down sufficiently enough to enter between the channel margins. Wood loads will continue to increase as more trees fall and bridging pieces decompose, break and then enter the channel. Measurable increases in the amount of LW with time since initial beetle infestation have both positive and negative effects on channel form and function. Although forest MPB-infestation has peaked in the study area, streams are still early on a curve of rapidly increasing wood loads that are beginning to affect streams and have the potential to dramatically increase the carbon base of regional stream ecosystems.

No description available.