1,720,978 research outputs found
Runoff Process of a Subarctic Canadian Shield Lake Stream System
No full textTitle: Runoff Processes of a Subarctic Canadian Shield Lake Stream System, Author: Corrine A. Mielko, Location: ThodeMany lake-stream networks consisting of numerous lake basin elements linked by
surface flow channels occupy Precambrian Shield and lowland areas in the boreal region.
To investigate the processes causing flow generation and seasonal severance of flow
connection in the lake-stream system, a chain of lakes in northern Canada was studied in
2004. Water balance shows that rapid and substantial runoff from the local basin slopes
during the snowmelt period led to a rise of lake levels above their outlet elevations to
generate outflow. Continued summer evaporation caused draw down of lake storage
below the outflow thresholds, represented by the lake outlet elevations. Outflow ceased
and the lakes became disconnected. Summer rainfall in a semi-arid environment was
insufficient to overcome storage deficit to re-establish flow connectivity among all lakes.
Individual lake outflow generation is dependent on the rate of runoff delivery, the initial
antecedent storage level with respect to the critical outflow threshold level and the ratio
of catchment to lake area. For the drainage system as a whole, streamflow interruption or
continuity depends on linkage of its lake-stream sub-units. The principle of fill and spill
governs runoff generation and flow connection between the lake elements. This principle
is applied to model the flow along a chain of lakes, taking account of antecedent storage
in individual lakes, their storage change calculated through water balance and the
thresholds to be exceeded for outflows to occur.ThesisMaster of Science (MS
River Regimes of Northern Ontario
Get PDF The period of observation necessary to obtain representative mean monthly values for precipitation, temperature, and streamflow is about fifteen years. At present there is a paucity of meteorological and streamflow records of such length. This makes hydrological investigations in northern Ontario difficult. River regimes of northern Ontario are found to exhibit general characteristics. More specifically, runoff peaks occur in spring due to snowmelt, and secondary fall peaks occur due to rainfall. The regimes can be classified into four types based upon qualitative comparisons of annual flow response patterns. River regimes in northern Ontario exhibit spatial variation. Rivers to the northwest have lower flow magnitude due to decreased precipitation, and tend to have flow "buffered" by the many small lakes located there. Rivers to the southeast have more pronounced spring melt peaks resulting from greater winter snow accumulation. Fall contributuion to total annual runoff increases to the northwest. The colder winter conditions of northern Ontario is reflected in a tendency of winter contribution to annual yield to decrease towards the northwest. Seasonal runoff is affected by meteorological conditions. Temperature has a marked effect on spring streamflow as rising temperature causes snowmelt. Summer flow reflects the effects of both temperature and precipitation. Precipitation has a pronounced effect on fall runoff. Winter runoff is dominated by baseflow only as temperatures are low and precipitation is snow which accumulates until spring. An attempt to produce equations for predicting seasonal monthly flow was unsuccessful. Meteorological stations are too sparsely distributed to provide representive data necessary for producing such equations. There is a need to increase the meteorological and streamflow station network in northern Ontario to enable a more comprehensive study of the hydrologic processes.ThesisCandidate in Philosoph
DROUGHTS, RAINFALL AND RURAL WATER SUPPLY IN NORTHERN NIGERIA
No full textKnowledge concerning various aspects of drought and water scarcity is required to predict, and to articulate strategies to minimize the effects of future events. This thesis investigated different aspects of droughts and rainfall variability at several time scales and described the dynamics of water supply and use in a rural village in northeastern Nigeria. The parallel existence of measured climatic records and information on famine/folklore events is utilized to calibrate the historical information against the measured data. It is shown that famines or historical droughts occurred when the cumulative deficit of rainfall fell below 1.3 times the standard deviation of the long-term mean rainfall. The study demonstrated that famine chronologies are adequate proxy for drought events, providing a means for the reconstruction of the drought/climatic history of the region. Analysis of recent changes in annual rainfall characteristics show that the series of annual rainfall and number of rain days experienced a discontinuity during the 1960's, caused largely by the decrease in the frequency of moderate to high intensity rain events. The periods prior to and after the change point are homogenous and provide an objective basis for the estimation of changes in rainfall characteristics, drought parameters and for damarcating the region into sub-zones. Rainfall variability was unaffected by the abrupt change. Furthermore, the variability is independently distributed and adequately described by the normal distribution. This allows estimates of the probability of various magnitudes of thresholds of variability. The effects of droughts and rainfall variability are most strongly felt in rural areas. Analysis of the patterns of water supply and use in a typical rural village revealed that the hydrologic system is driven by the local rainfall. Perturbations in the rains propagate through the system with short lag time between the various components. Where fadama aquifers occur, they offer a major supplement of water for six to seven months during the dry season. Under traditional systems, the pattern of water withdrawal from the fadama aquifers is designed to accommodate the diverse interests of different groups and to minimize the potential for conflict. The results contribute to our understanding of drought and water scarcity and are useful in various practical applications.Doctor of Philosophy (PhD
Water Level Regimes in a Swamp
No full textThis research studies the spatial and temporal variations of the watertable of Beverly Swamp (Southern Ontario), within the context of the hydrology of the area. Fieldwork was conducted from April to November, 1977, and it concentrated on the monitoring of water levels at selected sites in the swamp. Results indicate that there is a strong interaction between streamflow and subsurface flow, which led to a classification of swamp water level regimes. In general, streams entering the swamp tend to impose their regime on the surrounding aquifer which thus experiences a "periodically effluent" regime, with periods of marked influent flow. The flow of the streams starting at the swamp, instead, depends on the watertable of the surrounding aquifer, which experiences a "predominantly effluent" regime. The relationship between swamp water levels and outflow is analyzed in detail. At a seasonal scale, this relationship is non-linear, and at a reduced time scale it shows a series of hysteresis loops caused by two factors. The first is related to a translation time lag, and the second to different discharges resulting from a given watertable level. Stream level, evaporation and rainfall data are then used in a numerical model which synthesizes the water level hydrographs at several sites in the swamp. Finally, runoff regulation ability of the swamp is examined, and it is concluded that it is of small magnitude, noticeably only in small-volume, flashy inputs to the swamp.Master of Science (MS
Hillslope hydrology and runoff processes in a subarctic, subalpine environment
No full textWithin the subalpine zone of a subarctic basin, hydrological processes were studied on four hillslopes within 5 km2 in an attempt to determine the factors that cause the variability in the magnitude and timing of water balance components. The hillslope was chosen as the scale of study as it links process operating at the point with streamflow, and exhibits strong contrasts in microclimate, vegetation, frost and soils, providing an ideal natural laboratory. Hillslopes showed strong asymmetry in the timing and magnitude of processes during the melt and summer period. On slopes with well drained soils and seasonal frost, vertical hydrological exchanges predominate over the entire year and slopes rarely contribute runoff for streamflow. In contrast, hillslopes underlain with permafrost and/or poorly drained soils with a capping organic layer produce strong lateral fluxes. Water balance information highlighted the principal factors that lead to differences in process magnitudes and timing. This information is important in understanding basin hydrology, as streamflow is a summation of lateral fluxes from slopes. The presence of ice-rich layers blocking soil interstices encourages runoff by restricting drainage. Runoff exhibits a two-layer flow system consisting of quickflow (pathways in the porous organic layer, pipes, rills, and interconnected depressions) and slowflow (pathways in underlying mineral soils and highly decomposed and compacted peat). Quickflow controls the shape and timing of the runoff hydrograph, which is influenced by properties of hillslope wetness and organic layer thickness. Recession analysis revealed variable source areas for runoff generation and highlighted the role of wetness-controlled hydrologic connectivity of a slope segment. Results from this thesis have implications for water resource inventories and predicting hydrologic behaviour of subarctic, subalpine hillslopes.Doctor of Philosophy (PhD
The Effect of Organic Terrain and Surface Modification on Active Layer Development
Get PDF[Missing pages: xi, 3, 20, 21] During the summer of 1995, ground energy balance was calculated for six organic soils at different stages of development and nine mineral soils subject to forced modification near Resolute, N.W.T. Ground temperature, frost and water tables, and soil moisture were monitored at each site on 9 m2 plots, allowing inter-comparisons in an attempt to assess how active layer development was related to changes in soil structure, hydrology and boundary conditions. In organic soils, both the degree of humification and the position of the water table were the principal controls on active layer thaw. Developing organic soils with water tables near the surface had deeper thaw and warmer soil profiles than decomposing organics. The presence of ground ice also limits thaw depth because of large latent heat requirements for ice melt. In organic soils, both conduction and convection of heat are important processes. A feedback mechanism may exist whereby wetland organics are maintained by keeping the active layer shallow through a reduction in heat transfer when dry. The responses of mineral soils to changing boundary conditions were inconclusive. Modifications to surface albedo, rainfall, snowfall and soil structure all affected soil parameters. Decreased albedo and increased snow cover had the greatest influence on active layer thaw when compared with unmodified conditions of the previous year. Placing a gravel pad over surfaces modified thaw depths in both mineral and organic soils. The results of this study show the importance of hydrologic conditions, properties of surface organic layer, soil heterogeneity and ground ice on active layer thermodynamics. In all soils, heat flowing into the permafrost was the greatest component of the ground energy expenditure, followed by heat consumed in phase change and lastly by sensible heat used in warming the active layer. Current numerical models of active layer development are simplified, and this study shows that complexities not accounted for in models may hinder their ability to predict active layer responses to changing environments.Master of Science (MSc
Stochastic Operation Management Model for a Multi-Reservoir Inter-Basin Water Resource System
No full textThe discrepancy between the quantity and regime of water consumption and natural river flow usually gives rise to the need to create a multi-reservoir inter-basin water resource system to redistribute the river flow temporally and spatially. As the economic value of water increases and inexpensive sources of water supply diminish, the development of an optimal operation management model becomes more and more important. In this thesis, a stochastic operation management model composing of two integrated models of stochastic multi-site flow generation model and deterministic Dynamic Programming optimization model is developed to determine the optimal operation of a multi-reservoir inter-basin water resource system. The stochastic multi-site flow generation model is used to generate synthetic now series as input to the optimization model. In this model. the stochastic nature of historical flows to reservoirs, i.e. auto-correlation and cross-correlation, is explicitly considered. The deterministic Dynamic Programming optimization model is developed to determine the optimum operation policies for each of the many synthetic flow series through application of the optimization model to the multi-reservoir inter-basin water resource system. The approach of separating these two models will overcome the curse of dimensionality encountered in existing DP optimization models while allowing the stochastic nature of inflows to be incorporated into the optimization process and resulting optimum operation policies. The real case study approach, selection criteria and description of case study area, Lar-Kalan-Latian water resource system in Tehran, Iran as a multireservoir inter-basin water resource system is discussed. The superiority of a real case study in comparison with a hypothetical or abstract one is demonstrated. A comprehensive review and identification of stochastic multi-site now generation models and discussion of available flow generation computer programs are presented. The statistical analysis of historical monthly and annual now data of the case study, setting up of HEC-4 program as direct method and SPIGOT program as disaggregation technique, and generation and verification of synthetic monthly and annual flow series for the case study are discussed. The comparison of HEC-4 and SPIGOT synthetic flow series with historical data shows the effectiveness of SPIGOT program against HEC-4, even for the short historical flow input data. A detailed review and discussion of the Dynamic Programming techniques and development of deterministic DP optimization model for the multi-reservoir inter-basin water resource system is carried out. The generation, comparison, statistical analysis, and reliability characteristics of optimum monthly operation polices determine by applying the developed DP optimization model is discussed. The comparison of optimum operation with historical operation demonstrates the usefulness and improvement of optimum operation upon historical operation. It is further concluded that the DP optimization model is not sensitive to the type of stochastic flow generation model used to generate synthetic flows. Finally, the development of optimum operation reliability characteristics demonstrates the application ofstochastic operation management model in planning and operation of multi-reservoir inter-basin water resource system.Doctor of Philosophy (PhD
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
