<p> Chesterfield Inlet drains an area of 290,000 km^2, between Great Slave Lake and northern Hudson Bay, of predominantly continuous permafrost terrain. The 220-kilometre-long inlet may be used as an important navigation link to Baker Lake and potential pipeline sites. The inlet forms a complex network and is characterized by strong tidal forcing.</p> <p> A one-dimensional numerical model, using a weighted, implicit, finite difference scheme, was modified for application to the network. Sparse matrix techniques were incorporated into the model to speed Gaussian Elimination in the solution of the equations.</p> <p> Tidal constituents, derived from admittance calculations, were used to predict water levels at eight tide gauge locations. Tidal predictions at Sandpiper Island were used as the downstream boundary condition for the numerical model, while tidal predictions at the other gauge locations were used in the model calibration.</p> <p> The observed and model-computed water levels are in good agreement over the lower half of the inlet. Appreciable differences between the observed and computed values were encountered in the upper reaches. Although some of these discrepancies are attributable to errors in the upstream boundary condition and schematization of the model, there is evidence to suggest that time and range errors may exist in some of the recorded tidal data.</p> <p> The variation in the phase and amplitude of the tide throughout the inlet is determined through an examination of the tidal constituents and the model results. Power spectra of the observed and model-predicted water levels reveal that nonlinear interactions of the major tidal constituents take place in the upper portion of the inlet.</p> / Thesis / Master of Engineering (MEngr)

No description available.

Includes bibliographical references (p. B1-B24)

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. May 30, 2016. / In statistics, a model is as good as the data fed to it. Data about hydrological events continues to grow rapidly over the years, with different variables being recorded on a continuous scale. These variables can be interpreted and used in a different manner among disciplines. Thus, choosing the right variables and interactions among variables is an important statistical step in building a good and accurate model. This dissertation involved the development of a statistical model which can be used to predict weekly water level within the Okavango river in northern Namibia. The parameters of the statistical mixed model were estimated based on two methods for longitudinal data, the Generalised Estimating Equations (GEE) which is a well known method of parameter estimation in longitudinal data analysis when the observed variables are correlated, and the Restricted Maximum Likelihood Estimation (REML) which is a likelihood based approach method, unlike the GEE. Using cross-validation and a simulation study, the GEE method of estimation was found to be less accurate and inconsistent in terms of prediction of parameter estimation of water level while the well known REML was found to predict the water level with a good degree of accuracy, consistency and with lower variance. Parameters from a simulation study have also shown less bias in REML method and predicted the cross-validation test-set with less bias. / GR 2016

Water availability is a critical limiting element in semi-arid ecosystem productivity and presents particular challenges in Sahelian countries such as Senegal. The landscapes are characterized by the presence of two common semi-arid shrubs (Piliostigma reticulatum and Guiera senegalensis), both of which may be important hydraulic regulators in these water-limited ecosystems. Dry season observations revealed higher moisture levels in soil surrounding the shrub shallower roots relative to bare soil. This observation led us to hypothesize that these shrubs may participate in a natural irrigation phenomenon termed as "hydraulic redistribution" (HR). This dissertation reports on three studies performed to ascertain the existence of and investigate the characteristics of this hypothesized phenomenon. The first study investigated seasonal variability in soil water and shrub root patterns. Soil moisture content declined steadily in the 0.9-1.2 m depth range and increased in the 0.2-0.4 m depth range, which supports the HR hypothesis. The second study quantified plot scale water balance fluxes. Notably, shrub water uptake from the water table served as a crucial contribution to the system water balance. The third study investigated the magnitude and dynamics of HR during the dry season. Crop-shrub associations were evaluated from measurements of soil moisture and potential, root sap flow and plant physiological measurements. This study proved the existence of HR and quantified the HR magnitude (~0.1 mm d⁻¹). For shrubs and annual crops in close association with shrubs, HR clearly provides a mechanism for drought-stress avoidance and maintenance of plant physiological functions. At the landscape scale, the interplay between shrub root morphology and HR may play a vital role in ecosystem function with practical implications for nutrient cycling and water balance in arid ecosystems. / Graduation date: 2006

The Long Point wetland complex is one of the most significant coastal wetland systems in the Great Lakes, containing a diverse mosaic of wetland vegetation communities that have developed in response to water level fluctuations due to natural climate variability. Natural short-term water level variations are important for promoting wetland productivity and diversity, but long-term water level changes resulting from human-induced climate change can have serious and long-term consequences on the integrity and health of wetlands. The historical response of the wetland to water level fluctuations was quantified and modelled to provide an indication of how the wetland may respond to future projected water level changes - water level fluctuations are used as a surrogate for climate change. A spatiotemporal trend analysis was conducted within a geographic information system (GIS) to determine the effects of water level conditions on wetland vegetation and land cover at the wetland complex at Long Point, Ontario for seven years from 1945 to 1999. The spatiotemporal trend analysis documented changes in the structure and composition of the wetland complex in response to declining and rising water level conditions. During drier periods, there were significant increases in the amount of drier emergent and meadow vegetation, especially within the Inner Bay and northern portion of the outer peninsula. There was less fragmentation and complexity in the wetland as these drier communities expanded forming larger continuous patches of vegetation. During wetter periods, open water increased and there was a predominance of wetter emergent and meadow communities in the wetland. Drier vegetation communities became interspersed with water creating a more fragmented convoluted wetland landscape. The historical response of the wetland vegetation and land cover to water level fluctuations was then simulated with three different wetland models developed in the GIS. A rule-based model, a probability model, and a transition model were developed to assess wetland response to future water level changes. The models were evaluated using simple statistical methods. The transition and rule-based models performed the best and were successful in predicting over 80 % of the wetland vegetation distribution correctly. The probability model was the least successful, predicting only 55 % of the response correctly. The GIS proved successful in documenting wetland response to historical water level fluctuations and providing insight into the potential impacts of future climate change though water level fluctuations on the Long Point coastal wetland complex. The spatiotemporal analysis and wetland modelling advance the role of GIS in wetland management and analysis. They are practical methods within a GIS that can be used to assess the impacts of climate change on wetland systems and to document and model wetland change in other coastal wetlands of the Great Lakes.

The Long Point wetland complex is one of the most significant coastal wetland systems in the Great Lakes, containing a diverse mosaic of wetland vegetation communities that have developed in response to water level fluctuations due to natural climate variability. Natural short-term water level variations are important for promoting wetland productivity and diversity, but long-term water level changes resulting from human-induced climate change can have serious and long-term consequences on the integrity and health of wetlands. The historical response of the wetland to water level fluctuations was quantified and modelled to provide an indication of how the wetland may respond to future projected water level changes - water level fluctuations are used as a surrogate for climate change. A spatiotemporal trend analysis was conducted within a geographic information system (GIS) to determine the effects of water level conditions on wetland vegetation and land cover at the wetland complex at Long Point, Ontario for seven years from 1945 to 1999. The spatiotemporal trend analysis documented changes in the structure and composition of the wetland complex in response to declining and rising water level conditions. During drier periods, there were significant increases in the amount of drier emergent and meadow vegetation, especially within the Inner Bay and northern portion of the outer peninsula. There was less fragmentation and complexity in the wetland as these drier communities expanded forming larger continuous patches of vegetation. During wetter periods, open water increased and there was a predominance of wetter emergent and meadow communities in the wetland. Drier vegetation communities became interspersed with water creating a more fragmented convoluted wetland landscape. The historical response of the wetland vegetation and land cover to water level fluctuations was then simulated with three different wetland models developed in the GIS. A rule-based model, a probability model, and a transition model were developed to assess wetland response to future water level changes. The models were evaluated using simple statistical methods. The transition and rule-based models performed the best and were successful in predicting over 80 % of the wetland vegetation distribution correctly. The probability model was the least successful, predicting only 55 % of the response correctly. The GIS proved successful in documenting wetland response to historical water level fluctuations and providing insight into the potential impacts of future climate change though water level fluctuations on the Long Point coastal wetland complex. The spatiotemporal analysis and wetland modelling advance the role of GIS in wetland management and analysis. They are practical methods within a GIS that can be used to assess the impacts of climate change on wetland systems and to document and model wetland change in other coastal wetlands of the Great Lakes.

Pinus patula Schiede ex Schlect. & Cham. is the most widely planted softwood species for both pulpwood and saw timber in the South African forestry industry. High mortality of this species, often in excess of 20%, following planting is currently of major concern and has the potential to limit future deployment for commercial timber. Water stress is often reported to be a cause of mortality during regeneration in commercial forestry plantations yet, prior to 2007, there was no published research on the water relations of P. patula during regeneration in South Africa. This, together with questions raised by the industry as to the role of using water in the planting operation, initiated the series of studies conducted for this thesis. Water planting (application of water into the planting hole at the time of planting) of P. patula seedlings has been used commercially to reduce post-planting water stress and buffer against potentially extreme weather conditions immediately after planting. However, the primary role of the water, as well as its success in increasing survival following planting, has never been critically assessed. Since the use of water in the planting operation is expensive, it was essential that the benefits to using water were quantified, in terms of survival and growth, and justified, in terms of any monetary investment. In addition, there was a lack of local studies investigating the physiological characteristics of P. patula seedlings, particularly their tolerance to low soil water availability. To understand the role of water during the regeneration of P. patula in terms of plantation management and seedling physiology, a variety of research methodologies were used that included: applied field trials, multivariate methods (a retrospective investigation), pot trials and the development of a simple financial model. Four field trials were implemented to test the response in P. patula survival to water applied at planting. Two trials each were situated in the KwaZulu-Natal (KZN) Midlands and Mpumalanga Escarpment. The first trial at each site was planted in spring (October) and the second in summer (February). Watering treatments consisted of different quantities of water used in the planting operation and included 0.5 litres, 2 litres, 4 litres and no water (dry plant). Only at the spring planted trial in the KZN Midlands was survival of the dry planted seedlings significantly lower than that of the seedlings planted with water, at 90 days after planting. This may have been due to low rainfall during the week before and two weeks after planting, or the small size of the seedlings used in the trial. Application of 0.5 litres of water to the planting pit was sufficient to increase survival to a level equivalent to that where 2 or 4 litres of water was used, yet only increased soil moisture in the area immediately surrounding the seedling. This suggested that the role of the water applied during planting was increased root to soil contact. Overall, these four trials indicated that planting with water had the potential to increase survival only when soil water availability was low and rainfall sporadic. There was no effect of water applied at planting on early tree growth. While the results of the four field trials provided an indication of the effect of planting with water on subsequent survival of P. patula seedlings, there was concern that the results of the four trials may not be a true reflection of a dynamic situation. Survival in response to water applied at planting may vary from year to year and across forestry regions due to the unpredictable nature of rainfall and high air temperatures during the planting season, as well as the wide range of forestry sites across which P. patula seedlings are planted. To improve our understanding, a database of 58 trials was compiled where water and dry planting had been carried out. In this way it was possible to investigate whether the results from the four field trials were reflected in a range of previously conducted field trials implemented across time and space. The trials incorporated into the dataset were all planted to P. patula between 1990 and 2005 in the summer rainfall region of southern Africa. Data related to the climate, local weather, physiography and site management at each trial were also included. Summary statistics, linear correlation and multiple regression were used to determine if site-associated variables were related to an increase in survival in the water relative to the dry planted treatments. The analyses indicated that for all 58 trials, survival was lowest during the summer months, regardless of planting treatment. Planting with water was most likely to increase survival when used during spring, autumn and winter planting, although (as with the four applied field trials) there was no overall significant relationship between water planting and survival. Based on these results it was anticipated that an understanding of the water stress physiology of P. patula seedlings was required to explain the observed trends from a more fundamental perspective; if planting with water did not always increase survival, why not? Three pot trials were conducted to increase the understanding of the water relations of P. patula seedlings. These trials were also used to provide benchmark physiological data related to stressed (water) and unstressed seedlings. The first pot trial highlighted the importance of root plug moisture at the time of planting for increasing subsequent survival. The subsequent two pot trials were aimed at investigating the interaction between planting stock quality (as determined by measures of size) and soil water availability and the effect on survival, growth and physiology of P. patula seedlings. These results indicated that P. patula seedlings were not as sensitive to high air and soil temperatures (above 30°C) and low soil water availability (below -1.5 MPa) as previously thought. The seedlings were able to tolerate low soil water availability for several weeks and, following rewatering, were able to recover from moderate and severe water stress (a shoot water potential of below -1.5 MPa). This data supported the results from the four applied field trials and retrospective study of 58 trials, where the application of water to the seedlings at planting did not substantially increase survival. In the pot trials, stomatal conductance started to decrease when shoot water potential approached -0.8 to -0.9 MPa. Stomatal closure occurred at a shoot water potential between -1.2 MPa to -1.5 MPa. Mortality due to water stress occurred only in response to extended periods of low soil water and was associated with a shoot water potential of below -3.0 MPa. There was variability between seedlings in their potential for survival and growth. Inherently bigger seedlings had a greater capacity for new root growth following planting. New root growth, as well as a greater mass of new roots, was associated with higher shoot water potentials and higher rates of transpiration under conditions of low soil water availability. This indicated that seedling quality, as determined by size, may play a role in sensitivity to water stress. The field trials, retrospective study and pot trials indicated that the practice of planting with water was not always critical to the survival of P. patula seedlings. A simple financial model was developed to estimate whether planting with water represented a cost that could be used as a decision criterion, given certain growth parameters and management scenarios. The data projected by the model were also compared to actual research data for water versus dry planting (and the inclusion of an insecticide in the water). While these comparisons were specific to the parameters included in the model for this study, as well as the results of the research trials used in the benchmarking exercises, the model indicated that; 1) costs for planting with water were likely to be recovered only when no blanking (replacing of dead trees) was carried out, with capital invested at a low return rate (3%), 2) including an insecticide in the water increased the likelihood of cost recovery, and 3) site quality had an impact on the increase in survival required to recover planting method costs, with a greater percentage increase in survival required on lower quality sites. Lower quality sites often have a lower mean annual precipitation (associated with higher rainfall variability), or shallow soils (associated with lower soil water availability) and therefore are also likely to be sites where foresters may want to use water to reduce (drought related) mortality. The impact of site quality is thus also an important factor to include in any decisions regarding planting methods (i.e. using water) and their costs. Further investigations should be aimed at examining; 1) the interaction of root plug size (as determined by container type) and soil water availability on growth and physiology of P. patula seedlings, 2) the methods of grading seedlings within a population to select those that have a high potential for survival and growth, and 3) the effects of soil water availability on the physiology, survival and growth of P. patula cuttings, as well as other pine species and hybrids grown in South Africa, such as P. elliottii, P. elliottii x P. caribaea and P. patula x P. tecunumanii. It is likely that the proportion of forestry regions planted to these hybrids will increase in the future. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2008.

As water depth increased, fourth instar larvae of the mosquito Aedes aegypti required progressively more time to reach the pupal stage, more individuals died or were disabled and the resulting adults were significantly smaller. Water depth affected females more severely than males and the developmental time of larvae was affected more than adult mass. Time spent by fourth instar female larvae in the feeding zone during the first five hours predicted the time to subsequent pupation. Thereafter, mean feeding time was a determining factor of subsequent adult mass. With increasing water depth, both the prepupal resting period and mean time spent in the feeding zone per feeding bout increased, whereas behavior frequency (determined by an activity index) decreased.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvi, 180 p.; also includes graphics (some col.). Includes bibliographical references (p. 168-180). Available online via OhioLINK's ETD Center