In this thesis we have performed an experimental investigation into steady-state two-phase flow behaviour at the core and pore scales and visualised the fluid distributions using medical and fast synchrotron X-ray computed tomography. We performed an experimental study of steady-state, drainage relative permeability curves with CO2-brine and N2-deionised water, on a single Bentheimer sandstone core with a simple two-layer heterogeneity over reservoir conditions of 10.3-20.7 MPa, 38-91°C and 0-5 mol kg-1 NaCl brine. We demonstrate that, if measured in the viscous limit, relative permeability is invariant with changing reservoir conditions, and is consistent with the continuum-scale multiphase flow theory for water wet systems. Furthermore, we show that under capillary limited conditions, the CO2-brine system is very sensitive to heterogeneity in capillary pressure, and by performing core-floods under capillary limited conditions, we produce effective relative permeability curves that are flow rate and fluid parameter dependent. We show that the appropriate conditions for measuring intrinsic or effective relative permeability curves can be selected simply by scaling the driving force for flow by a quantification of capillary heterogeneity and use this methodology to make measurements of CO2-brine relative permeability for target CO2 storage reservoirs in the UK. A new type of pore-scale flow behaviour was identified, that we term dynamic connectivity, using fast synchrotron X-ray computed tomography to image the capillary dominated steady-state flow of N2 and 1.5 mol kg-1 KI brine at 50°C and 10 MPa. Non-wetting phase flow occurred via a stable connected pathway at low capillary numbers and through a series of transient connections between a network of static ganglia with a dynamic connectivity at increasing capillary numbers. We speculate that changes observed in the strength and character of hysteresis between drainage and imbibition during capillary and viscous dominated core-scale experiments is a consequence of this pore-scale flow mechanism.

This thesis presents the first detailed multiproxy provenance study of the modern Nile catchment, together with Oligocene-Recent sediments of the offshore Nile cone, and demonstrates for the first time that the palaeodrainage of the Nile has remained relatively stable over the last 30 Ma. Detrital mineral and bulk-rock analyses of modern river, wadi and bedrock samples demonstrate the role of basement lithology, sedimentary recycling, and modern geomorphological features in controlling the composition of sediment reaching the Nile cone. The bulk provenance signature of the modern Nile is dominated by the input of basic detritus from the Cenozoic Ethiopian Large Igneous Province. Detrital zircon signatures are dominated by variations in bedrock lithology, and the availability of easily-eroded Phanerozoic cover sediments. These represent an important source of detritus to the river and are characterised by the presence of strongly negative εHf populations at c. 600 and 1000 Ma, and significant populations of pre-Neoproterozoic grains. Young zircon grains derived from Ethiopian Cenozoic volcanic rocks are also recognised in samples from the Blue Nile, Atbara and Nile trunk. The Sr, Nd and Hf signature of Oligocene Nile cone sediments can only be explained if there is significant input of mafic material being received from the hinterland. The Ethiopian Large Igneous Province represents the only possible source for this detritus, indicating that the Nile has been connected to the Ethiopian Highlands since this time. Zircons with U-Pb ages and hafnium isotope signatures compatible with the Ethiopian LIP have been supplied to the Nile cone since at least the Miocene (16 Ma). Such zircons were not observed in Oligocene 2 delta sediments, but Sr, Nd and Hf isotope data for Oligocene delta muds as old as 31 Ma require significant mafic input. The combined U-Pb and Hf-isotope zircon dataset for Nile catchment and cone sediments represents a significant archive that documents the evolution of the North African crust, in particular highlighting phases in the development of the Arabian Nubian Shield and amalgamation of Gondwana in late Neoproterozoic times.

This PhD thesis explores the effects of spatial arrangements of riparian landscape elements and food resources on community and population dynamics of small mammals within a braided section of the River Tagliamento in Italy. The main research questions addressed were: (1) Which variables affect small mammal diversity on river islands? (2) Do small mammal populations inhabiting river islands differ in their life histories compared to riparian forest populations (the ‘island syndrome’)? (3) Is there a difference in the spatial behaviour of small mammals inhabiting the riparian forest compared to those on the islands? Three rodent species were used as focal species to address these questions: Apodemus sylvaticus, A. flavicollis and A. agrarius. The expectations were that small mammal dynamics did not fit completely island biogeography and life-history models developed for oceanic islands because islands in the present study are characterised by a low degree of isolation from the surroundings, by an ephemeral nature due to periodical flooding and by a low availability of food resources for small mammals. The main findings confirm these expectations, with the three species only partially following the predictions both at community and population ecology levels. Of the three species, A. sylvaticus was the most insular and more closely followed the predictions, in particular that of the island syndrome. Small mammal diversity on the islands was affected by island area, by the flooding dynamics and by resource availability. Finally, home ranges of A. agrarius were much larger on the islands than in the riparian forest. The findings suggest that river islands in the study area are a lower-quality habitat, partly due to their ephemeral nature, but the presence of habitat heterogeneity introduced by the islands allows for the rich community of small mammals to segregate, hence increasing species diversity at a landscape level.

The deterioration of the West African savannah in the last three decades is believed to be closely linked with about 0.5 C rise in temperature leading to evaporation losses and declining levels of the Volta Lake in Ghana. Although hydrological models can be used to predict climate change impacts on the regional hydrology, spatially-observed ground data needed for this purpose are largely unavailable. This thesis seeks to address this problem by developing improved methods for estimating energy and water fluxes (e.g. latent heat [ET]) from remotely sensed data and to demonstrate how these may be used to parameterize hydrological models. The first part of the thesis examines the potential of the Penman-Monteith method to estimate local-scale ET using groundbased hydrometeorological observations, vegetation coefficients and environmental data. The model results were compared with pan observations, scintillometer (eddy correlation) measurements and the Thomthwaite empirical method. The Penman- Monteith model produced better evaporation estimates (~3.90 mm day(^-1) for the Tamale district) than its counterpart methods. The Thomthwaite, for example, overestimated predictions by 5.0-11.0 mm day(^-1). Up-scaling on a monthly time scale and parameterization of the Grindley soil moisture balance model with the Thomthwaite and Penman-Monteith data, however, produced similar estimates of actual evaporation and soil moisture, which correlated strongly (R(^2) = 0.95) with water balance estimates. To improve ET estimation at the regional-scale, the second part of the thesis develops spatial models through energy balance modelling and data up-scaling methods, driven by radiometric measurements from recent satellite sensors such as the Landsat ETM+, MODIS and ENVISAT-AATSR. The results were validated using estimates from the Penman-Monteith method, field observations, detailed satellite measurements and published data. It was realised that the MODIS sensor is a more useful source of energy and water balance parameters than AA TSR. For example, stronger correlations were found between MODIS estimates of ET and other energy balance variables such as NDVI, surface temperature and net radiation (R(^2) = 0.67-0.73) compared with AATSR estimates (R(^2) = 0.31-0.40). There was also a good spatial correlation between MODIS and Landsat ETM+ results (R(^2) = 0.71), but poor correlations were found between AATSR and Landsat data (R(^2) = 0.0-0.13), which may be explained by differences in instrument calibration. The results further showed that ET may be underestimated with deviations of ~2.0 mm day 1 when MODIS/AATSR measurements are validated against point observations because of spatial mismatch. The final part of the thesis demonstrates the application of the ET model for predicting runoff (Q) using a simplified version of the regional water balance equation. This is followed byanalysis of flow sensitivity to declining scenarios of biomass volume. The results showed the absence of Q for >90% of the study area during the dry season due largely to crude model approximation and lack of rainfall data, which makes model testing during the wet season important. Runoff prediction may be improved if spatial estimates of rainfall, ET and geographical data (e.g. land-use/cover maps, soil & geology maps and DEM) could be routinely derived from satellite imagery.

Reconstructing drainage evolution has important implications for constraining long-term source-to-sink configurations. Furthermore, the analysis of ancient landscapes can support research in geomorphological concepts such as steady state and landscape evolution modelling. Techniques such as cosmogenic dating and morphometric analysis have rarely been applied to investigate the long-term drainage evolution of systems draining southern South Africa. This study focusses on the large-scale antecedent Gouritz catchment, Western Cape. Integrating provenance, cosmogenic and geomorphological (planform / morphometric indices) evidence indicates the trunk rivers are Cretaceous or older in age (i.e. principal topography of Mesozoic age). The trunk rivers fed huge volumes of sediment offshore during large-scale Mesozoic exhumation of southern South Africa with remnant coeval deposits in onshore extensional basins. However, there is a mismatch of onshore exhumation and offshore deposition and material is now found on the Falkland Plateau; separating source-to-sink by 6000 km. During exhumation, large scale pediments formed that grade to individual base levels and should be taken as individual features, not ‘surfaces’ correlated across the continent. A second phase of pediment evolution occurred in the mid-Cenozoic, dissecting the pediments and eroding small catchments into the Cape Fold Belt. These smaller order streams are strongly affected by the tectonic grain of the fold belt, whereas the trunk rivers are not, which is shown by variation in morphometric indices. The lack of correlation between catchment properties and denudation rates indicate the system has decoupled and that allogenic factors are now dominant. Due to the low rates of denundation, weathering is currently the rate limiting factor. However, during the early evolution of the catchment, tectonic activity was more dominant than the present day. The ancient catchment is in geomorphic steady-state, and highlights the need for further research into long-term landscape evolution, and linkage to offshore depositional records.

Sedimentological and diagenetic factors determine porosities and permeabilities within carbonate ramp deposits, and hence their potential reservoir properties. But information on variability of these characteristics on length scales of 102 km, the dimensions of some shallow-dipping, homoclinal ramps, is rare. This study, combining field and subsurface samples of carbonates of the Lower Miocene Euphrates and Jeribe Formations in the Zagros Basin, northern Iraq, demonstrates consistent microfacies but with diagenetic variations from proximal locations in the north-east to more basinal locations >100km to the south west. Microfacies analysis of the studied sections determines that the Lower Miocene carbonates were deposited in the inner ramp setting of the carbonate ramp and were affected by two diagenetic evolution stages. Dolomitization and dissolution processes have greatly affected the reservoir properties. The heterogeneity of porosity and pore connectivity in the studied units developed from the diagenetic overprint, where early dolomitization and dissolution have been shown to have significantly affected porosity and permeability values in the basinal locations, whereas early and burial cementation have reduced porosity and permeability in the north-east locations. Pore throat size, which controls fluid flow in reservoir rocks, is rarely established in heterogeneous carbonates, and in carbonate reservoirs complex pore networks occur. Thus it is crucial to investigate the factors governing reservoir quality in the carbonate rocks of the Euphrates and Jeribe Formations, potential carbonate reservoirs in Kurdistan. This study considers the factors affecting the distribution of porosity, permeability and reservoir quality using regional stratigraphy, outcrop sections, well logs and petrophysical analyses of core material from 10 wells, as well as a large suite of laboratory petrophysical measurements. Four main rock types have been identified based on the petrophysical properties, geological and diagenetic processes for the Euphrates and Jeribe Formations. Rock types I and IV were indicated as non-reservoir units and rock types II and III as reservoir rocks. This study reveals a lack of correlation between carbonate microfacies and reservoir properties, due to the variation in diagenetic process over distances of 10’s to 100 km. This study therefore demonstrates the need for following a rock-typing methodology when dealing with heterogeneous carbonates with varied diagenetic overprints, to create a static model framework appropriate for dynamic reservoir modelling.

The principal objective of this research programme was to conduct a re-examination of the basic nature of hydrological parameters of rainfall, infiltration and surface runoff. Experimental work using a specially designed laboratory catchment and a rainfall simulator is described. This equipment is regarded as a useful contribution to the study of hydrology and its description is given in the early part of the thesis. Basically the equipment consists of a soil catchment area that can be precisely inclined to any desired angle. Additional instrumentation then monitors the flow of water across the surface of, and through the soil catchment bed. Precipitation is provided by another specially designed unit that simulates rainfall at a particular rate and distribution. It is demonstrated that this equipment is capable of realistically simulating the water flow as it would occur on a natural catchment. It provides means of studying hydrological phenomena for a range of soil samples under precise control. A large amount of data was collected on the basic of laboratory experiments for a range of soil samples. From these data it was possible to develop a number of empirical formulae that conveniently summarise the inter-relationships between the principal hydrological parameters, namely rain intensity, runoff, infiltration and catchment slope. Known physical laws of fluid flow have been used in the derivation of the formulae. Previous hydrological work is reviewed and, where appropriate, is compared with the present study. Suggestions for further work are also outlined.

A relational database has been devised as a tool for the digitization of features relating to the sedimentary and geomorphic architecture of modern rivers and ancient fluvial successions, as derived from either original field studies or published examples. The system has been designed in a way that permits the inclusion of hard and soft data – comprising geometries and spatial and hierarchical relationships – referring to classified genetic units belonging to 3 different hierarchical levels, and assigned to stratigraphic volumes that are categorized in terms of deposystem boundary conditions and descriptive parameters. Several applications of the quantitative information generated through database interrogation have been explored, with the scope to demonstrate how a database methodology for the storage of sedimentary architecture data can be of use for both pure and applied sedimentary research. Firstly, an account is given of how the system can been employed for the creation of quantitative fluvial facies models, which summarize information on architectural styles associated with classes of depositional systems. The value of the approach is shown by contrasting results with traditional qualitative models. Secondly, database output on large-scale fluvial architecture has been used in the context of a comparative study aiming to investigate the role of basin-wide aggradation rates as predictors of fluvial architectural styles. The results contrast with what might be expected by commonly considered stratigraphic models; the main implication is the necessity to reconsider continental sequence stratigraphy models or their domain of applicability. This application further provides an example of how the methodology could be generalized to the study of the sensitivity of architecture to its controls. Thirdly, database output has been used to conduct a re-evaluation of previously-proposed approaches to the guidance of well-to-well correlations of subsurface fluvial channel bodies, applied in earlier studies. Making use of the same analogue information, a new probabilistic approach has been proposed as a way to inform or rank correlation panels of channel bodies across equally-spaced wells. Finally, the value of the system as an instrument for constraining object- and pixel-based stochastic structure-imitating models of fluvial sedimentary architecture is collectively demonstrated through a range of example applications employing database output.

In recent years, the input of trace metals into surface water systems has increased significantly, raising interest among scientists to better define water quality standards (WQS) at the catchment scale. Active mineral operations and other land use practices add to the naturally high metal concentrations of the surface waters in many parts of the world, and spatially and temporally impact the physico-chemical quality of water bodies. Regulatory authorities are well aware that it is important to consider chemical and toxicological principles, such as bioavailability, in the development of WQS; however, current metal WQS thresholds for surface waters are based on the dissolved or total element concentration alone. Furthermore, it is important to understand how the metal levels and bioavailable fractions change spatially and temporally, and how the natural and anthropogenic sources control the content and bioavailability of metals in the surface water of a catchment. This PhD research aimed to address this issue and improve the definition of water quality standards taking into account both water chemistry and metal speciation principles. The specific objectives of the project were to: identify natural and anthropogenic sources of metals in surface water systems, taking into account the natural environment (geology, mineralization, climate, etc) and past and present human activities; determine seasonal variations and their influence on the chemical speciation; and develop a methodology to characterise and quantify the spatial distribution of the metal species in the stream water and sedimentary environment. The Rapel River Basin in Central Chile was selected as field study region since it offers a diverse geology, hosts intense mineral exploitation and agriculture, and exhibits marked seasonal variations in the surface flow regime. One hundred surface water and sixty sediment samples were collected during the low (April-May, 2006) and high flow season (December, 2006–January, 2007; repeat water samples only). Statistical analysis methods were used to assess the statistical properties of the data and investigate the relationships between the parameters. Together with these, profile analysis and Piper diagrams were used to describe the water chemistry spatially and temporally along the rivers, and assess the water quality in relation to the chemistry of the sediment. Multivariate analyses, including cluster and principal factor analysis methods, were used to: study the complex associations among the water quality parameters and their relationship with the land use and geology; to determine the underlying geochemical processes; and quantify the relative contribution of natural and anthropogenic sources to the metal loads. Finally, chemical equilibrium and biotic ligand models (WHAM and PHREEQC, and BLM, respectively) were used to estimate quantitatively how the metals were partitioned in different species in the two hydrological regimes, and to identify the principal factors that control their bioavailability and toxicity. The approach developed in this research can be used to identify areas vulnerable to metal toxicity and suggest appropriate management strategies to protect water quality at the catchment scale. Areas with similar geochemical characteristics are distinguished, and effective water quality monitoring procedures can be designed given information on background geology and existing land use practices. In addition, the potential effect of metal releases to aquatic environment can be determined and the uncertainty estimated by the QA/QC can be integrated to the Cu risk assessment yielding realistic results and protective WQS.

No description available.