published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

The extent of revegetation in the Colorado River delta in Mexico is described, with emphasis on the return of native cottonwood (Populus fremontii ) and willow (Salix gooddingii) trees. Low-level aerial and satellite remote sensing methods were combined with ground surveys to census the vegetation in a 100 km reach of riparian corridor in Mexico. Although the invasive plant, saltcedar (Tamarix ramosissima), still dominates the riparian zone, native trees now account for 23% of the vegetation in the delta. Multi-band digital camera images obtained by aircraft were used to calculate the Normalized Difference Vegetation Index (NDVI) and scored for percent vegetation cover (NDVI:%C has r = 0.91***). A Thematic Mapper (TM) image taken concurrently with the aerial survey was similarly classified, and by comparing scenes on the TM and aerials, it was possible to calibrate NDVI with percent vegetation on the TM image. This information was used to conduct a change analysis relating flows in the Colorado River with summer vegetation patterns on TM images for the years 1992-1999. The results support the importance of pulse floods in restoring the ecological integrity of arid-zone rivers. This dissertation also compared transpiration rates of three Sonoran Desert riparian trees using sap flow and leaf temperature methods using constructed canopies (two of each species: Populus fremontii (cottonwood), Salix gooddingii (willow) and Tamarix ramosissima (saltcedar)) in an outdoor experiment in Tucson, Arizona. Canopies were measured over 11 days for both sap flow and canopy and air temperature differential (Tc-Ta) under non stressed and stressed conditions. Objective 1: to determine the strength of the relationship between transpiration (Et) and Tc-Ta to determine if Tc-Ta can be a useful remote sensing method to measure Et for these species. Objective 2: to compare Et rates among species, to determine if the invasive species, saltcedar, has higher Et rates or ecophysiological advantages over the native trees species. We conclude that the Tc-Ta method could be useful in estimating Et by remote sensing over riparian corridors, and that native trees are not at an ecophysiological disadvantage to saltcedar so long as sufficient non-saline soil moisture is available to support Et.

Between 1960 and 1991, the population of Rondonia, Brazil increased from 70,000 to 1.3 million. This increase occurred during the thirty-year period bracketing the rise to statehood, during which a rural population also became largely urban. Simultaneously, the loss of tropical rain forest in the state progressed at unparalleled rates. This dissertation examines some of the ways in which these two rapidly changing aspects of Rondonia's landscape are related to each other. The research project employs a framework grounded in realist philosophy, a flexible approach that facilitates research into processes that are unfolding at a regional scale but which occur within the context of broader national and international structures. Several kinds of connections between urban population growth and deforestation are examined, including land conversion for urban use, food consumption in urban areas, wood consumption for housing in urban areas, and power consumption in urban areas. Urban sprawl is found to be significantly and positively correlated with deforestation at the municipio level, but the absolute magnitude of urban sprawl is very small relative to total deforestation. No spatial correlation is found between urban settlement and the dedication of land to food crops. A weak but positive correlation is found between urban demand for timber and total deforestation, but the absolute magnitude of local timber demand is found to be very small in comparison to forest clearing. The recent diversification of the timber industry in order to absorb urban labor may have profound implications for demand on forest resources in the future. Electricity generation has been destructive of rain forest, and capacity already under construction is likely to have further such impacts. The cultural landscape of Rondonia reflects an orientation that is increasingly outward-looking. Rondonia's cities and towns are becoming more closely connected with one another and more fully integrated with the outside world. Early incentives to settle in Rondonia contributed to deforestation, but the curtailment of these incentives did not curtail deforestation. Rondonia is a place caught between two opposite pressures: the pressure to preserve the rain forest and the pressure to participate in the world economy as consumers.

Morphology related to the South Saskatchewan River in the Outlook Saskatoon region is basically a product of the complex relationships between fluvial activity, glacial and lacustrine history and surficial materials. / During deglaciation, the river experienced numerous major changes before becoming incised in its present location. Channel scars and deltaic-alluvial deposits are widespread. / The present valley proper shows marked local variation in overall width; terrace characteristics; occurrence of slumping, and features of the valley floor including floor and river widths, gradients, braiding, meandering, channel bars and islands, and flood plain characteristics and development. Differences are largely the result of (a) pronounced variations in the resistance to erosion of materials of the valley sides and floor; (b) the influence of an alluvium-filled gut, underlying the river in the south, on width and slumping; and (c) the influence, in the north, of sharp bends which were inherited from a braided network of early high-level channels.

Morphology related to the South Saskatchewan River in the Outlook Saskatoon region is basically a product of the complex relationships between fluvial activity, glacial and lacustrine history and surficial materials. / During deglaciation, the river experienced numerous major changes before becoming incised in its present location. Channel scars and deltaic-alluvial deposits are widespread. / The present valley proper shows marked local variation in overall width; terrace characteristics; occurrence of slumping, and features of the valley floor including floor and river widths, gradients, braiding, meandering, channel bars and islands, and flood plain characteristics and development. Differences are largely the result of (a) pronounced variations in the resistance to erosion of materials of the valley sides and floor; (b) the influence of an alluvium-filled gut, underlying the river in the south, on width and slumping; and (c) the influence, in the north, of sharp bends which were inherited from a braided network of early high-level channels.

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Previous studies found that during a rainfall event, pre-event water, which exists in the catchment before the event, may appear in significant amounts in the stream stormflow hydrograph. Pre-event water is predominantly groundwater. Among the mechanisms that have been proposed to explain the rapid mobilization of pre-event water from hillslopes are: (1) groundwater ridging (GWR) i.e. the rapid rise of a water table in environments, where the capillary fringe, or the zone of tension saturation, is very close to the ground surface and (2) the Lisse Effect (LE) i.e. the rapid response of a groundwater level to pressurized pore air in the unsaturated zone. Published literature explains that GWR is caused by the application of a small amount of water on the ground surface. On the LE, it is explained that pressurized pore air acts at the water table, resulting in a rapid rise of the water level in a well, screened below the water table. These explanations are insufficient on the physical processes involved in GWR and the LE. The objectives of this study were: (1) to use the commonly observed catchment hydrological processes i.e. tensiometric pore water pressure, shallow groundwater levels, rainfall data and the hydraulic properties of soils, to quantify and describe the physical processes involved in GWR and the LE mechanisms; (2) to perform laboratory experiments, in order to understand the physical processes involved in the LE; and (3) to develop a mathematical theory that can describe the physical processes in the LE. Results indicated that GWR and the LE are caused by the addition (elevation) of potential energy in water within the capillary fringe. In GWR, the additional energy is from the intense rainfall. In the LE, the additional energy is from compressed pore air in the unsaturated zone. In both mechanisms, the added energy diffuses through the capillary fringe, as a downward pressure wave, releasing the tension forces in water. As soon as the downward pressure wave-front arrives at the water table, the water table begins to ascend, as an upward pressure wave. The ascending water table steepens the hydraulic gradient, which results in the rapid groundwater fluxes, without the recharge of the water table by the infiltration profile. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.

Hillslope mechanisms and processes are a complex and dynamic set of interactions, but are nevertheless vital components of hydrology due to their critical interactions with surface and groundwater (Lorentz, 2001a). In order to observe and quantify these flow generating mechanisms, the Weatherley subcatchment was selected where the components of streamflow generation have been studied and can be quantified separately. Surface, shallow subsurface and the deeper groundwater interactions are particularly important when quantifying runoff generation from within hillslope, riparian and wetland zones as they are the dominant runoff generating zones within the Weatherley catchment. These components of flow are important to quantify for the further study of flow generation mechanisms, their dynamics and fluxes at the hillslope and small catchment scale, low flow contributions, climate change as well as the consequences of land use change (Lorentz, 2001b). Transfer functions were found to be the best adaptation of hydrograph separation for distributed hydrological modelling purposes when attempting to quantify the various streamflow hydrograph components. In this study, the runoff components were simulated along transects using the HYDRUS-2D model, where the simulated soil water dynamics are compared with the observed tensions and water contents at different depths within the soil profile in order to quantify the contributing hillslope fluxes to streamflow generation. The 2001 data set was used with the rainfall and potential evapotranspiration data being converted into rates according to the breakpoint rainfall data. The HYDRUS-2D modelling exercise is performed to calculate the variety of flux rates (timing and quantities) within the subcatchment, so that the overall stream hydrograph can be properly deduced when modelling this catchment with transfer functions in the future. An understanding of the driving forces as well as the behaviour of sources and flow paths was extracted from this thesis, along with gaining some knowledge about the mechanisms and behaviour of streamflow generating mechanisms at the hillslope and small catchment scale. Troch et al (2003) clearly encapsulates the essence of modern day catchment hydrology in stating that hillslope response to rainfall remains one of the most central problems of catchment hydrology in order to quantify catchment responses. The processes whereby rainfall becomes runoff continue to be difficult to quantify and conceptualise (Uhlenbrook et al., 2003) and this is because the characterisation of subsurface water flow components is one of the most complex and challenging tasks in the study of the hydrologic cycle (Achet et al., 2002). Since trying to understand the temporal and spatial variability of moisture content and the subsurface flow mechanisms is a complicated problem (Achet et al., 2002), an attempt is made in this thesis to gain insights into the temporal and spatial variability of soil tensions and soil moisture content at various depths on hillslope transects by combining modelling exercises with field observations. From this modelling, the hillslope water balance and contributing fluxes are derived in effort to augment, at a later stage, the hillslope response functions. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Several hydrological studies claim that available water resources in a catchment are affected by large scale afforestation, especially where the regional rainfall is considered marginal for the support of silviculture. Nevertheless, the mechanisms and magnitude of the perturbations to the receiving water resources due to afforestation are still not clearly understood. To improve this understanding an intensive hydrological experiment has been initiated in the small grassed Weatherly catchment of the Mondi, North East Cape Forests. Details of the soil water dynamics on the Molteno formations in the catchment have been be studied. This research presents a description and first results of the establishment of an experiment which comprises monitoring the water budget of the grassed catchment prior to the afforestation of the catchment to plantations of exotic trees. The studies currently include, monitoring the infiltration and redistribution of soil water on a hillslope as well as monitoring of interflow mechanisms and localised mechanisms of soil water accumulation influenced by the topography and geology of the catchment. In addition to the intensive soil water monitoring, specific experimentation has been conducted at various locations on the hillslope. These comprise macropore flow process studies and 2-dimensional tracer experiments. Details of these experiments as well as the automated soil water and groundwater monitoring instrumentation are presented. An intensive soil survey on a 30 m x 30 m grid as well as a comprehensive measurement strategy of soil physical and hydraulic properties are highlighted. A review of 2-dimensional numerical hillslope soil water process models is also presented. Results from this research show that on hillslopes underlain by Molteno sandstones localised perched water tables form. These water bodies, upon reaching a critical height above the bedrock cascade downslope as interflow recharging the water bodies downslope. The response to infiltration increases downslope and in the toe region interflow occurs readily in response to rainfall compared to the midslope where substantial rain needs to infiltrate. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.

Terracettes are a widely occurring form of micro-relief found throughout regions displaying various climatic and environmental conditions. Much speculation surrounds the processes responsible for their formation and development. An investigation of these micro-forms, their associated soil physical properties, sustaining mechanisms, and their relationship to slope stability was undertaken in Giant's Castle Game Reserve, KwaZulu - Natal Drakensberg, South Africa. The study showed that relationships between terracette morphology and soil physical properties within the Reserve are few, and that current soil conditions cannot be used to infer process related to terracette formation. However dry bulk density data indicated that soil creep is the dominant formative mechanism within the Reserve. Throughflow at riser surfaces was the dominant sustaining mechanism, with needle ice growth, wind, surfacewash and animal disturbance contributing minor retreat at both treads and risers. Aspect played an important role in determining soil physical characteristics. It was inferred that terracettes imparted stability to the slopes on which they are found, and with continued retreat at both treads and risers the slope was again placed under conditions of instability. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.