Lacking efficient means of digital data storage and processing, previous regional flood frequency analyses seldom considered the spatial dimension of the problem explicitly. As a result, insufficient use was made of spatial autocorrelation; of associations with other variables or of topological inter-relationships such as proximity (near a water body), containment (within a $2\rm\sp{nd}$ orderwatershed) and orientation (bearing and azimuth). Spatially-implicit methods also tended to marginalise the importance of flood-generating mechanisms--which vary continuously in space--and which combine at each location to yield the total flood risk. In this study, the most current nonparametric and L-moment (parametric) methods for flood frequency analysis (FFA) are supplemented by geostatistical and GIS techniques. Three spatial approaches are adapted for FFA: scientific visualization of random fields; characterization of spatial associations; and hierarchical spatial models of flood parameters. Three spatial models are investigated for the L-moments of flood observations: the L-skew is taken as an average within regions (polygons); the L-coefficient of variation is modelled using kriging (continuous space); and the L-mean is estimated locally (point) or from maps if local records are unavailable. L-moments are used to estimate the parameters probability distributions used to describe floods. Average daily maximum (AM) flood flows for Central and Eastern Canada are analysed. (Abstract shortened by UMI.)

Cette etude recouvre la periode de la fin du Pleistocene superieur et l'Holocene. Elle met en relief, par analyse comparative, les influences locales et regionales que subissent des accumulations eoliennes du nord-ouest du Yukon selon les conditions paleoenvironnementales et paleoclimatiques de l'epoque. L'etude porte sur les loess de Bluefish datant de la fin du Pleistocene, des accumulations eoliennes holocenes de sommet de falaise dans les Ramparts de la vallee de la riviere Porcupine et des sediments eoliens de la plaine alluviale de la riviere Bluefish, de l'Holocene moyen. Plusieurs facteurs, tels la disponibilite des sediments de la source, le climat (direction des vents, humidite de l'air et temperature) et la couverture vegetale controlent la dynamique eolienne. Ils peuvent etre definis par une serie d'indicateurs dont la granulometrie, les teneurs geochimiques (CaCO3, matiere organique, Al2O3, Fe2O3, etc ...), la susceptibilite magnetique, l'exoscopie des grains de quartz, l'orientation des depots eoliens, taux de sedimentation, etc ...; eux-meme determines par analyses sedimentologiques et chronologiques. Cette etude permet de constater que l'edification de phenomenes eoliens locaux peuvent etre consequents de phenomenes d'envergure regionale et renferment ainsi des informations relatives a des changements d'ordre paleoclimatique et paleoenvironnemental. Les sources potentielles ainsi que les divers episodes d'intensite eolienne ont ete identifies. A partir de ces resultats, une tentative de reconstruction des conditions climatiques et environnementales qui ont permis l'edification des depots eoliens dans le nord-ouest du Yukon, pendant le Pleistocene superieur et l'Holocene, est presentee.

Lors de la derniere glaciation du Wisconsin, la calotte glaciaire s'est arretee au flanc oriental des Monts Richardson qui separent les Territoires du Nord-Ouest du Territoire du Yukon. La majeure partie de la region septentrionale du Yukon fut alors epargnee de l'invasion par l'inlandsis laurentidien. Cet evenement a provoque la reorganisation du systeme hydrographique du nord du Yukon, la submersion de trois grands bassins de la region creant ainsi de vastes lacs alimentes par les eaux de fonte du glacier continental. Les evenements glaciaires sont bien documentes dans la litterature, mais la description et la chronologie relative des evenements qui ont eu lieu en marge de la limite glaciaire, et en particulier ceux convernant les paleolacs, font souvent defauts. Afin de pallier a ce manque d'information, la these presente l'etude des caracteristiques sedimentologiques du material des plages d'un des anciens lacs. Par cet etude nous tentons de verifier l'hypothese suivante: l'etude des caracteristiques des sediments des paleoplages permet de determiner la frequence des episodes glacio-lacustres dans la plaine d'Old Crow. De plus, nous voulons repondre aux deux objectifs principaux: connai tre l'environnement dans lequel les lacs se sont mis en place et les evenements qui ont conduit a leur drainage.

La riviese Porcupine qui prend naissance dans les monts Ogilvie, au Yukon septentrional, est caracterisee par de nombreux meandres quand elle traverse la plaine de Bluefish. Cette plaine, etablie dans un bassin tectonique datant du Tertiaire, a accumule au cours du Cenozoique des sediments qui, a l'Holocene, ont ete entailles par la riviere. La photo-interpretation des depots superficiels de la riviere Porcupine a l'interieur de la plaine de Bluefish a permis d'identifier trois categories de depots meubles soit du gravier, du sable et du limon. Une etude sedimentologique a ete effectuee le long de la riviere Porcupine sur une distance d'environ 84 kilometres. A l'interieur de cette section, 6 coupes stratigraphiques ont ete etudiees et 87 echantillons ont ete retenus pour des fins d'analyses sedimentologiques. Les resultats de l'analyse granulometrique ont ete soumis a une analyse bivariees: le diagramme Md/Qd (phi) de Krumbein. La combinaison de cette analyse avec celles des datations radiocarbones et a la position geographique des coupes etudiees, a permis de reconstruire l'histoire alluviale de la riviere Porcupine dans la plaine de 14 ka B.P. a aujourd'hui. Les principaux resultats sont: (1) Un encaissement rapide (50 m), entre 14 ka et 12 ka B.P. suite a une decharge fluvio-glaciaire qui mit en place des terrasses d'erosion. (2) L'edification d'une terrasse liee a une phase de sedimentation intense associee a la fin de la decharge glacio-lacustre. (3) L'edification d'une terrasse moderne a quelques metres de la surface de la riviere Porcupine. Cette terrasse est en equilibre avec l'hydrologie actuelle.

The distribution of 2,690 gold-silver-bearing occurrences in the Nevada Great Basin was examined in terms of spatial association with various geological phenomena. Analysis of these relationships, using GIS and weights of evidence modelling techniques, has predicted areas of high potential where little or no mining activity exists. Mineral potential maps for sedimentary ("disseminated") and volcanic ("epithermal") rock-hosted gold-silver mineralization revealed two distinct patterns that highlight two sets of crustal-scale geologic features that likely control the regional distribution of these deposit types. Mineral potential maps predicting the distribution of gold-silver-bearing occurrences successfully predicted nearly 70% of the total number of known occurrences. In blind tests, the sedimentary and volcanic rock-hosted mineral potential maps predicted 10 out of 12 and 5 out of 5 occurrences, respectively. The key mineral predictor factors, in order of importance, were determined to be: geology (including lithology, structure, and lithotectonic terrane), geochemistry (indication alteration), and geophysics. Areas of elevated sedimentary rock-hosted mineral potential are generally confined to central, north-central, and north-eastern Nevada. These areas form a conspicuous "V"-shape pattern that is coincident with the Battle Mountain-Eureka (Cortez) and Carlin mineral trends and a segment of the Roberts Mountain thrust front, which bridges the southern ends of the trends. This pattern appears to delineate northwest-southeast-trending crustal-scale structural zones, here termed the "Carlin" and "Cortez" structural zones. Mineralizing processes were focused along these structural zones. The Carlin and Cortez structural zones are considered to be transcurrent features representing a long-lived, deep-crustal or mantle-rooted zone of weakness. Areas of elevated volcanic rock-hosted mineral potential are principally distributed along two broad and diffuse belts that trend (1) northwest-southeast across Nevada, parallel to the Sierra Nevada, and (2) northeast-southwest across northern Nevada, extending diagonally from the Sierra Nevada to southern Idaho. The first belt corresponds to the Walker Lane shear zone, a wide region of complex strike-slip faulting. The second, here termed the " Humboldt shear(?) zone", may represent a structural zone of transcurrent movement. Volcanic rock-hosted mineralizing was closely tied to the southward and westward migration of Tertiary magmatism across the region (which may have been mantle plume-driven). Latest movement along the Humboldt shear(?) zone is constrained between ∼42-30 Ma (sedimentary rock-hosted mineralization) and ∼17-14 Ma, (most recent igneous activity along the northern Nevada rift zone). (Abstract shortened by UMI.)

A physicochemical database is constructed by linking chemical and stable isotope analyses of the Ottawa River and its tributaries to properties of their catchment basins by overlaying maps of the properties and maps of the catchments utilizing a Geographic Information System (SPANS). Data include bedrock geology, forest type and extent, soil properties such as the organic carbon content of soils, land use, elevation, discharge, precipitation, and temperature. Deuterium ($\delta$D) and oxygen ($\delta\sp $O) isotopes for the Ottawa River and its tributaries in the spring range from $-$71 to $-$92$\perthous$ and $-$9.4 to $-$12.7$\perthous$ VSMOW, respectively. In the fall these values are $-$51 to $-$89$\perthous$ and $-$5.1 to $-$11.7$\perthous$ and the discharge weighted average at the mouth of the river, based on monthly samples, is $-$82 and $-$10.9$\perthous$. From these data, the average isotopic composition of precipitation that falls in the Ottawa River basin is calculated to be $-$103.8 and $-$14.5$\perthous$ for $\delta$D and $\delta\sp $O, respectively. Based on forty years of daily meteorological and discharge data and utilizing GIS, annual evapotranspiration for the Ottawa River basin is calculated to be 51%. Due to climatic and soil conditions, the upland silicate basins and lowland carbonate basins average 40 and 65% evapotranspiration, respectively. Combined evaporation and evapotranspiration calculations apportions 43% of the water losses in the Ottawa River basin to transpiration plus interception. Peaks in discharge occur in the spring due to snow melt, and in the late fall due to the cessation of transpiration by frost and are directly out of phase with precipitation inputs which are greatest during the summer. This implies that riverine baseflow is maintained exclusively by groundwater recharge during the non-growing season. Both the susceptibility of minerals to weathering and soil respiration rates increase downstream such that low-elevation-low-latitude tributaries, draining easily weathered carbonate terrains with thick productive high-pCO$\sb2$ soils, and containing areas with relatively high population density and intense agricultural land use, are characterized by: (1) high concentrations of total dissolved solids (TDS), DIC, Ca$\sp{2+}$, Mg$\sp{2+}$, Sr$\sp{2+}$ have $\delta\sp $C$\rm \sb{DIC}$ of approximately $-$8$\perthous$, and low $\rm \sp‡Sr/\sp†Sr$ ratios, representing a geogenic signal; and (2) high concentrations of Na$\sp+$ Cl$\sp-$, and K$\sp+$, representing a mixed anthropogenic and geogenic signal. Conversely, the sparsely, populated, high-elevation-high-latitude, chemically resistant, silicate shield catchments are characterized by low TDS, DIC, SO$\sb4\sp{2-}$, Ca$\sp{2+}$, Mg$\sp{2+}$, NO$\sb3\sp-$, Sr$\sp{2+}$, higher Si and Fe$\rm \sb{total}$, have $\rm \delta\sp C\sb{DIC}$ of roughly $-$16$\perthous$ and high $\sp‡$Sr/$\sp†$Sr ratios, and their anthropogenic signal is subdued to non-existent. Isotopic composition of dissolved inorganic carbon ($\rm \delta\sp C\sb{DIC}$) for the lowland carbonate and upland silicate tributaries is about $-$8 and $-$16$\perthous$, respectively. This suggests that (1) the source of DIC to the Ottawa River is soil respiration and carbonate weathering, (2) exchange with the atmosphere is unidirectional or volumetrically unimportant, and (3) in-river respiration and photosynthesis are not significant influences on the river carbon budget. (Abstract shortened by UMI.)

A field experiment, involving direct manipulation of surface microclimate, was undertaken in the continuous permafrost zone to examine the influence of climatic fluctuations on solifluction rates and movements throughout the active layer. Movements and soil temperature were measured continuously from 1993-1997 using five electro-mechanical meters and thermocouple cables on an 8$\sp\circ$ colluvial slope in Hot Weather Creek valley, Ellesmere Island. Natural variation of movement among the years and the meters was measured until summer of 1996 when surface climatic treatments (surface warming, wetting, a combination of these two, and cooling) were performed. The longer-term effects of the treatments were monitored until August 1997. Near-surface measurements alone do not provide an accurate picture of solifluction in areas with two-sided freezing ("cold" permafrost) because there can be substantial variation in movement rates at depth. In addition, multi-year average rates potentially hide a considerable range of annual variability and do not allow for the examination of a relationship between climatic fluctuations and annual movement. (Abstract shortened by UMI.)

No description available.

No description available.

No description available.