Thesis advisor: Noah Snyder / The dynamics of river suspended sediment, derived from soil erosion, is critical for understanding floodplain and coastal wetland evolution, as well as reservoir sedimentation. Although the U.S. Geological Survey (USGS) has collected > 105 suspended sediment concentration (SSC) samples, data availability is often sparse or altogether lacking for large river transects. Landsat derived SSC measurements have proven accurate enough to supplement USGS datasets, allowing unprecedented spatial analysis of SSC trends throughout large river systems (Dethier et al. 2020). Here, I build on this approach by applying it to higher spatial and temporal resolution datasets. I have derived suspended sediment concentrations from the Sentinel-2 satellite sensor through a cluster and regression approach. To increase the number of training samples, I constructed SSC-discharge rating curves for all in-situ USGS stations. This has constrained the uncertainty of Sentinel-2 derived SSC to less than a factor of two, which has proven adequate for large rivers. In combination with the Landsat record, this allows for a multi-decadal analysis of sediment transport dynamics across multi-dammed systems. This study applies these methods to the Chattahoochee River in Georgia and Alabama, USA. Using observations from 1984 to 2022, there exists pronounced decreases in SSC downstream of dams along the river, with downstream reaches never regaining the same values as upstream observations. Also evident is a decreasing trend in SSC temporally, which could be indicative of changing land-use practices. Code for this project is publicly available at github.com/ivalencius/sentinel-ssc. / Thesis (BA) — Boston College, 2023. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Scholar of the College. / Discipline: Earth and Environmental Sciences.

Arid and semiarid river systems in Western Queensland, Australia, are characterized by the unpredictable and highly variable nature of their hydrological regimes as a result of the episodic nature of rain events in the region. These dryland rivers typically experience episodic floods and extremely low or no flow periods. During low or no flow periods, water persists only in relatively wide and deep sections of the river channels, which are called 'waterholes'. These isolated waterholes serve as refugia for aquatic species during protracted intervals between floods. In such discontinuous riverine habitat, dispersal of freshwater species may be achieved only during wet seasons, when water is flowing in rivers and the nearby floodplains. Obligate aquatic species occur in habitats that represent discrete sites surrounded by inhospitable terrestrial landscapes. Thus, movements are very much limited by the physical nature and arrangement of the riverine system. In addition, the distribution of a species may be also largely dependent on historical events. Landscape and river courses continually change over geological time, often leaving distinct phylogenetic 'signatures', useful in reconciling species' biology with population connectivity and earth history. The main aim of this study was to resolve the relative importance of contemporary and historical processes in structuring populations of two freshwater species in Western Queensland river systems. To address this aim, a comparative approach was taken in analysing patterns of genetic variation of two freshwater invertebrates: a snail (Notopala sublineata) and a prawn (Macrobrachium australiense). Mitochondrial sequences were used for both the species. In addition, allozyme and microsatellites markers were employed for N. sublineata. These species have similar distributions in Western Queensland region, although N. sublineata appears to be extinct in some catchments. M. australiense is thought to have good dispersal abilities due to a planktonic larval phase in its life cycle and good swimming capabilities, whereas N. sublineata is thought to have limited dispersal abilities, because of its benthic behaviour and because this species is viviparous. It was hypothesised that these freshwater invertebrates, would display high levels of genetic structure in populations, because physical barriers represented by terrestrial inhospitable habitat, are likely to impede gene flow between populations inhabiting isolated river pools. Genetic data for the two species targeted in this study supported this hypothesis, indicating strong population subdivision at all spatial scales investigated (i.e. between and within catchments). This suggests that contemporary dispersal between isolated waterholes is relatively restricted, despite the potential good dispersal abilities of one of the species. It was hypothesised that levels of gene flow between populations of aquatic species were higher during the Quaternary (likely movements of individuals across catchment boundaries) and that they have been isolated relatively recently. There is evidence that historically gene flow was occurring between populations, suggesting that episodic dispersal across catchment boundaries was likelier in the past. Episodic historical movements of aquatic fauna were facilitated by higher patterns of river connectivity as a result of the climate changes of the Pleistocene. Because the two species targeted in this study exhibit analogous spatial patterns of evolutionary subdivision it is likely that they have a shared biogeographic history. The unpredictable flow regime of rivers in Western Queensland is likely to have considerable effects on the genetic diversity of aquatic populations. First, if populations of obligate freshwater organisms inhabiting less persistent waterholes are more likely to experience periodic bottlenecks than those inhabiting more persistent ones, they would be expected to have lower levels of genetic diversity. Second, if populations inhabiting less persistent waterholes periodically undergo local extinction with subsequent recolonisation, there should be higher levels of genetic differentiation among them, due to the founder effects, than among those populations inhabiting more persistent waterholes. Contrary to the first prediction, the observed levels of genetic diversity in both N. sublineata and M. australiense were high in both more persistent and less persistent waterholes. There was no tendency for genetic diversity to be lower in less persistent than in more persistent waterholes. However, when Cooper waterholes were ranked in order of persistence, positive correlation between water persistence time in waterholes and genetic diversity was detected in N. sublineata but not in M. australiense. Contrary to the second prediction, highly significant genetic differentiation was found among populations from both less persistent and more persistent waterholes. This indicates that not only populations from less persistent but also those from more persistent waterholes were very dissimilar genetically. This study demonstrated the importance of both contemporary and historical processes in shaping the population structure of obligate freshwater species in Western Queensland river systems. It has indicated that contemporary movements of freshwater species generally are extremely limited across the region, whereas episodic dispersal across catchment boundaries was possible during the Pleistocene, due to different patterns of river connectivity.

The primary aim of this research was to develop and test a conceptual model of the geomorphological impacts of river regulation, based on a review of relevant international literature. It was motivated by the fact that there is very little local information on the topic, and it was intended that the model might provide a starting point for assessing the impact of impoundments on South African river systems. At present most research in South Africa on the impact of impoundments is undertaken from an ecological perspective. In order to manage our water resources sustainably it is necessary to have a better understanding of our river systems. South Africa is characterised by a variable climatic regime and, in order to supply water to the various user sectors of the nation, dams have to be larger than elsewhere in the world, to trap most of the mean annual runoff and provide a reliable water store (Alexander, 1985). South African dams have been designed to reduce the variability of a naturally variable regime. The impact of flow regulation in dryland rivers has been described as 'ecologically catastrophic at every level.' It is therefore hardly surprising that the impact of these dams on the natural functioning of rivers is substantial. The conceptual model showed that there are many responses to river impoundment, which are varied and complex, both in time and space. Responses or secondary impacts depended on the nature and degree of the primary impact or process alteration, on the sediment and flow regime of the river. High flows were affected in all cases and low flows were affected in most cases. The simplest form of change was Petts' (1979) concept of 'accommodation' of the regulated flow within the existing channel form. More complex responses occUrred where the channel perimeter was unstable, or where tributaries introduced fresh sediment loads. The river could adjust its long profile, cross sectional area and substrate composition by aggradation or degradation. The conceptual model was used in the Building Block Methodology to predict impoundment impacts at Instream Flow Requirement workshops on the Berg, Komati and Bivane rivers. It was also used in assessing the impact of the Sandile Dam on the Keiskamma river. Tributary junctions were identified as likely sites of change, and the morphology of bars at these junctions was investigated. Due to the number of variables affecting the sediment and flow regime in the system, and due to the fact that the primary impacts were not substantial, it was not possible to come to any decisive conclusions. It would seem that the dam is well located in the catchment, and, because the water is not heavily utilised, the secondary impacts are not great. The conceptual model was found to be a useful basic tool which might contribute to a better understanding of our river systems, and ultimately to improved sustainable resource management.

No description available.

A new Maximum Likelihood Criterion (MLE) suitable for data which are recorded at unequal time intervals and contain auto-correlated errors is developed. Validation of the new MLE criterion has been carried out both on a simple two - parameter reservoir model using synthetical data and on a more complicated hillslope model using real data from the Pukeiti Catchment in New Zealand. Comparison between the new MLE criterion and the Simple Least Squares (SLS) criterion reveals the superiority of the former over the latter. Comparison made between the new MLE and the MLE for auto-correlated case proposed by Sorooshian in 1978 has shown that both criteria would yield results with no practical difference if equal time interval data were used. However, the new MLE can work on variable time interval data which provide more information than equal time interval data, and therefore produces better visual results in hydrologic simulations.

published_or_final_version / Geography and Geology / Master / Master of Philosophy

No description available.

Subsurface oil and surface seep samples from the Niger Delta Nigeria, Tano and Cape Three Points Basins in Ghana, and the Orcadian Basin in Scotland were analysed using an organic geochemistry approach. Source organofacies, oil thermal maturity and the effect of alteration processes were evaluated, with the aim of developing a better understanding of the origin, nature and type of petroleum present. Biomarker analyses suggested that undegraded oils are found with biodegraded oils with a range of levels of biodegradation in the Niger Delta. On the commonly used Peters and Moldowan scale of biodegradation, the samples rank between PM level 0 and 7. The Ghanaian and Scottish oils and seeps showed a range of biodegradation levels between PM level 2 and 7. Biodegradation appeared to be the major control on the composition and physical properties of the oils and seeps from Niger Delta and Ghana while there is evidence that a stage of water washing was important for the Scottish seeps. Key aspects of the biodegradation process were reflected in the variable occurrence of hopanoids and other biomarkers. 25-Norhopanes were detected in all samples biodegraded in subsurface reservoirs but absent in seeps degraded at surface conditions. This was observed for both the Ghanaian and Nigeria samples. The inverse relationship of hopane to 25- norhopanes in the Niger Delta is presented for the first time. This evidence supports the hypothesis that 25-norhopanes are a product of hopane demethylation. Furthermore a pathway for the formation of 25-norhopane from 25-norhopanoic acid by decarboxylation is evidence by nature of the covariation in relative concentration of these compounds. Seeps from Scotland show that only moderate levels of biodegradation (PM 3) have significantly reduced monoaromatic and triaromatic steroids abundances. The most likely cause for this is by water washing at surface conditions. Reservoir temperature and oil charge histories appeared to have had a significant influence on the extent of biodegradation in the Niger Delta. The late migration of oil from deeper hotter subsurface regions to shallow reservoirs accounts for the presence of undegraded oils amidst the biodegraded oils in the Niger Delta.

The research undertaken for this Ph.D. thesis concerns the dispersion of solutes in sinuous open channel flows. The aim of the work is to address the void in knowledge and understanding of mixing and transport processes in natural watercourses. The influences of plan form curvature and non-uniform cross sectional shape on transverse and longitudinal mixing are specifically addressed. Experimental work was undertaken on the Flood Channel Facility at HR Wallingford Ltd. This involved creating a pseudo natural sand channel within the concrete meander plan form of the facility, and then stabilising the form. Tracer studies using instantaneous injection to investigate longitudinal mixing and continuous point source release to study transverse mixing were performed. Fluorescent tracer was used. Measurement was by six Turner Design Field Fluorometers in pump through mode and these were digitally logged. Detailed hydrodynamic measurements were made using a two-dimensional Laser Doppler Anemometer (LDA) fitted with a 14mm fibre-flow probe. The resulting data has undergone robust analysis and detailed interpretation. The conclusions are that the dominant processes in mixing, in the natural channel form studied, are shear effects. Simple equations for the prediction of flow fields have been investigated and validated against LDA measurements. It has been possible to make accurate predictions of the transverse and longitudinal mixing coefficients from the predicted flow fields. These predictions have been shown valid for the variations in mixing coefficients over the meander cycle and with discharge.

This thesis draws from data collected over thirteen months of fieldwork working with “Boaters”, a boat-dwelling itinerant group on the waterways of Southern England. In the first of three parts, the thesis focusses on the individual motivations (economic, personal and political) behind becoming a travelling Boater, and on how one acquires the requisite skills and knowledge to become part of a community of practice on the waterways. Boaters on the whole do not have a sense of being an ethnically distinct group and, as such, this thesis interrogates what kind of an identity is being created or reinforced when individuals recognise themselves as Boaters. This part further deals with the specific temporal experience of boating (commonly known as “boat time”) that creates a shared experiential pattern between Boaters, and also examines the informal networks of trade, exchange and barter which enmesh Boaters in a web of reciprocal relationships. In the subsequent part, the focus of the thesis widens to take in the boating “community” as it is imagined. It asks how the concept of community is rhetorically constructed and corporately enacted on the inland waterways and identifies the creation of an emic and local conception of community. In the third part, the focus widens further still in order to interrogate the troubled relationships between Boaters and sedentary populations and between Boaters and agents of the State. By looking at Boaters’ different (essentially nomadic) understandings of locality and political organisation, this thesis attempts to more broadly explain the fraught relationship between state agencies and itinerant populations. The thesis concludes that the community of Boaters is constructed through the shared understandings which emerge due to the Boaters experiencing much of their world as being flexible, fluid and unfixed. Boaters are bound by acts of dwelling together on the waterways, acts that emerge from the specific material conditions of boat life, and further from acts of support where Boaters bind together for the security of the group against antagonistic outsiders and the interventions of agencies of the state.