Abstract This Special Publication contains contributions for two meetings held to explore the links between geoscience and engineering in rivers and reservoirs (surface and subsurface). The first meeting was held in Brazil and, as a result, the volume contains many contributions from Brazil. The second was held in Edinburgh, and produced contributions from modern rivers in the USA, China, India and Scotland. The geological record from Carboniferous to Recent is represented. A range of outcrop techniques are presented along with statistical techniques used to identify patterns in the time series and spatial sense. The book is intended to cover the cross-disciplinary interest in rivers and their sediments, and will interest geologists, geomorphologists, civil, geotechnical and petroleum engineers, and government agencies. Some of the papers collected here demonstrate longer term impacts of human activity on rivers and how these might change the future geological record and, more importantly in the short term, impact on the UN Global Sustainability Goals.

Abstract It has been said that large rivers are the bloodlines of continents, and the Mississippi River system is the most prominent bloodline in North America. The Mississippi drainage stretches from the Rocky Mountains in the western USA to the Appalachian Cordillera in the east, and sediment from this vast area is then routed to the alluvial–deltaic plain of south Louisiana and the basin-floor fan in the deep Gulf of Mexico (GoM). Origins of the Mississippi system can be traced to the Late Cretaceous–Early Paleocene reorganization of North American drainage. However, integration of a continental-scale Mississippi drainage is a Late Neogene phenomenon, and sediment routing to the GoM has changed significantly over multiple timescales in response to a variety of large-scale natural forcing mechanisms and to human activities. This paper reviews large-scale change in drainage, sediment routing and sediment storage for the Mississippi system over timescales of 150 myr, where tectonic and geodynamic processes dominate, the last 150 kyr, where Milankovitch climate and sea-level changes dominate, and the 150 year period of the twentieth and twenty-first centuries when human activities have fundamentally altered the sediment routing and dispersal system.

Abstract The Colorado River in the SW of the USA is one of Earth's few continental-scale rivers with an active margin delta. Deformation along this transform margin, as well as associated intra-plate strain, has resulted in significant changes in sediment routing from the continental interior and post-depositional translation of older deltaic units. The oldest candidate deposits, fluvial sandstones of the Eocene Sespe Group, are now exposed in the Santa Monica Mountains, 300 km to the north of the Colorado River. Heavy mineral data from this basin indicate that sediment was sourced by a large river system, with some affinity to the early Pliocene Colorado River, but was unlikely to have been integrated across the Colorado Plateau. Sedimentological and mineralogical evidence from the earliest ( c. 5.3 Ma) unequivocal Colorado River-derived sediments in the Salton Trough provide evidence for a rapid transition from locally derived sedimentation. Lack of evidence for a precursor phase of suspended-load sediment suggests that drainage capture took place in a proximal position, favouring a ‘top-down’ process of lake spillover. Following drainage integration, significant changes in heavy mineral assemblages of fluvio-deltaic sediments, particularly evident from apatite–tourmaline and garnet–zircon indices, as well as U–Pb ages of detrital zircons, document the integration of the fluvial system to its present form and progressive incision of the Colorado Plateau from the Miocene to the present.

Abstract The integrated application of advanced visualization techniques – validated against outcrop, core and gamma ray log data – was found to be crucial in characterizing the spatial distribution of fluvial facies and their inherent permeability baffles to a centimetre-scale vertical resolution. An outcrop/behind outcrop workflow was used, combining the sedimentological analysis of a perennial deep braided outcrop with ground-penetrating radar profiles, behind outcrop optical and acoustic borehole imaging, and the analyses of dip tadpoles, core and gamma ray logs. Data from both the surface and subsurface allowed the recognition of two main architectural elements – channels and compound bars – and within the latter to distinguish between the bar head and tail and the cross-bar channel. On the basis of a well-constrained sedimentological framework, a detailed characterization of the gamma ray log pattern in the compound bar allowed several differences between the architectural elements to be identified, despite a general cylindrical trend. A high-resolution tadpole analysis showed that a random pattern prevailed in the channel, whereas in the bar head and tail the tadpoles displayed characteristic patterns that allowed differentiation. The ground-penetrating radar profiles aided the 3D reconstruction of each architectural element. Thus the application of this outcrop/behind outcrop workflow provided a solid database for the characterization of reservoir rock properties from outcrop analogues.

Abstract Conceptual models developed from modern distributive fluvial systems (DFSs) show a predictable spatial variation of facies progression from the margin to the interior of continental sedimentary basins. The Upper Cretaceous Serra da Galga Member of the Marília Formation has recently been interpreted to be a result of DFS deposition in the intracratonic Bauru Basin. This paper describes the spatial variations in stratigraphic architecture from the proximal to medial regions of the studied DFS and presents the implications of the recorded changes for fluvial reservoir characterization. The proximal areas are dominated by amalgamated channel-fill deposits and weakly developed, well-drained palaeosol profiles with only sparse floodplain deposits. The medial areas display a reduction in channel-fill deposits, an increase in the preserved thickness of floodplain deposits and the occurrence of sheetflood deposits and well-developed, poorly drained palaeosols. This spatial trend is accompanied by changes in the net : gross ratios of the geological bodies, forming possible high net : gross reservoirs in the proximal areas and reservoirs with very variable net : gross ratios in the medial areas. This down-system change in preserved stratigraphic architecture is evidenced for the first time in the studied sedimentary succession and follows the same pattern of facies progression described from modern examples of DFSs.

Abstract The Aptian Barbalha Formation records the beginning of the post-rift stage of the Araripe Basin. It consists predominantly of sandstones and mudstones interbedded with thin layers of bituminous black shales and conglomerates. The depositional and architectural features of the alluvial succession of the Barbalha Formation were characterized by detailed study and descriptions of the selected outcrops and analysis of well core data. In this study, two main depositional sequences were identified. The lower depositional sequence is more than 100 m thick and comprises a vertical facies succession composed of amalgamated, multistorey, braided fluvial channel sandstone bodies overlain by a widespread lacustrine black shale up to 10 m thick. The lacustrine black shales–carbonate mixed interval is known as the Batateira Beds and constitutes a regionally important stratigraphic correlation marker in the basin. This interval records the establishment of a large lake that experienced severe water-level fluctuations and anoxic events. The upper depositional sequence is 60–95 m thick, and mainly consists of thin, yellowish, medium- to fine-grained sandstones and variegated shales. The upper sequence rests unconformably on the lacustrine black shales of the Batateira Beds. Thin and discontinuous conglomerate beds at the base of the upper sequence laterally grade into coarse-grained sandstones. These coarse-grained sandstones are overlain by interbedded sandstones and mudstones organized in fluvial cycles. The upper and lower sequences of the Barbalha Formation are separated by an erosive unconformity, traceable throughout the study area, formed during a period of stratigraphic base-level lowering. This surface marks a change in the lower sequence from a dominantly fluvial depositional style, with amalgamated multistorey braided fluvial channel sand bodies, to a lacustrine system in the top to an eminently fluvial sedimentation, which in the basal section comprises amalgamated, multistorey, braided fluvial channel sand bodies, and in the superior section the amalgamated fluvial channels are overlain by floodplain and overbank sandstone bodies with fixed fluvial channel deposits, interpreted as a suspended-load-dominated fluvial system in the upper sequence. This change in the depositional style is accompanied by a reduction in grain size and a change in the fluvial regime, suggesting that the drainage system was restructured due to tectonic movements in the basin and climatic variations. In addition to the restructuring of the drainage basin, the characteristics of the discharge of the river system have changed, probably because of the more humid climatic conditions that dominated during the deposition of the upper sequence. The fluvial deposition in the lower sequence is associated with more ephemeral river systems, while the facies architecture of the upper sequence is associated with perennial systems and is suggestive of a suspended-load-dominated fluvial system. This fluvial system is capped by lacustrine deposits of the Crato Formation. The upper sequence grades upwards into the Crato Formation. The boundary between these two units is delineated by the presence of greenish calciferous shales that are covered by lacustrine laminated limestones and shales of Neoaptian age. Palaeocurrent readings from the fluvial deposits of both sequences display a consistent palaeoflow to the SE. Sedimentological and palaeontological evidence indicates a tectonic control on sedimentation and humid to subhumid climate conditions.

Abstract The period since the 1960s witnessed significant progress in our ability to decipher the clastic rock record from a wide range of sedimentary environments, and spanning many spatio-temporal scales, from millimetric to that of the sedimentary basin, and involving processes acting on timescales of seconds to millions of years. This review assesses advances in four areas of fluvial sedimentology: the nature of alluvial dunes, the role of fine-grained suspended sediment, the linking of facies models and channel planform, and the reconstruction of drainage networks within ancient sedimentary successions. The synthesis reveals that we require new thinking and research to: (1) address the range of stratification produced by dunes and their palaeohydraulic implications; (2) evolve new bedform phase diagrams capable of incorporating the reality that many fluids transport fine-grained sediment, both in flow and within the bed, which may significantly modify the bedform morphology and phase space when compared with existing bedform stability diagrams; (3) develop new alluvial facies models in which planform channel pattern is not the fundamental discriminant; and (4) re-establish consideration of process mechanics as the heart of developing ideas and debates concerning fluvial deposit preservation and alluvial architecture.

Abstract The Nhecolândia region covers the southern wetlands of the Pantanal basin in Brazil. Characterized by myriad shallow freshwater and alkaline–saline lakes, the distinct natural features of the Nhecolândia wetland make it highly sensitive to climate change and the effects of human activities. This paper summarizes the natural and social aspects that have affected this delicate wetland and potential future impacts. We analysed the response of the wetland to historical changes in climate and human activity and used this understanding to forecast the response of the wetland to future changes. The data presented here show that this region is particularly sensitive to alterations in the flood regime, droughts and deforestation, which are intrinsically related to both global and local changes in climate and the intensification of cattle-ranching activities, which include deforestation and the introduction of cultivated pastures.

Abstract The Spireslack surface coal mine exposes a section in the Carboniferous Lawmuir Formation (Brigantian) into the Upper Limestone Formation (Arnsbergian). This paper describes the stratigraphy exposed at Spireslack and, in so doing, names for the first time the Spireslack Sandstone, a distinctive erosively based, sandstone-dominated unit in the Upper Limestone Formation. The Spireslack Sandstone consists of two fluvial sandstone channel sets and an upper, possibly fluvio-estuarine, succession. From an analysis of their internal architectural elements, the channel sets are interpreted as a low-sinuosity, sand-dominated, mixed-load fluvial system in which avulsion and variations in sediment load played a significant part. The lower channel set appears to be confined to erosional palaeovalleys of limited lateral extent and significant relief. The upper channel set is much more laterally extensive and shows evidence of a generally lower sediment load with a greater degree of lateral accretion and flooding. Consequently, the Spireslack Sandstone may represent a system responding to base level changes of higher magnitude and longer duration than the glacio-eustatic scale commonly attributed to Carboniferous fluvio-deltaic cycles. The Spireslack Sandstone may represent an important correlative marker in the Carboniferous of the Midland Valley and may provide an alternative analogue for some Carboniferous fluvial sandstone stratigraphic traps.

Abstract The availability of historical streamflow data of the desired length is often limited and, in these situations, the ability to synthetically generate statistically significant datasets becomes important. We previously developed a highly efficient stochastic modelling approach for the synthetic generation of daily streamflow sequences using the systematic combination of a hidden Markov model with the generalized Pareto distribution (the HMM-GP model). Daily streamflow sequences provide limited information on various significant small duration flooding events exceeding the peak over threshold values, but these are averaged out in the daily datasets. These small duration intense flooding events are often capable of causing significant damage and are important in conducting thorough flood risk management and flood risk assessment studies. This paper presents upgrades to our HMM-GP stochastic modelling approach and examines its efficiency in simulating streamflow at a temporal resolution of 15 minutes. The potential of the HMM-GP model in simulating a synthetic 15-minute streamflow series is investigated by comparing various statistical characteristics (e.g. percentiles, the probability density distribution and the autocorrelation function) of the observed streamflow records with 100 synthetically simulated streamflow time series. The proposed modelling schematics are robustly validated across case studies in four UK rivers (the Don, Nith, Dee and Tweed).

Abstract River deposits are rich in sedimentological patterns that determine their petrophysical properties and industrial value (e.g. hydrocarbon reservoirs and aquifers), as well as providing each deposit with individual characteristics. Great variability in characteristics exists in modern river systems; their behaviour is expected to further diverge under environmental and climate change scenarios, and much greater variation exists when we consider all of geological time. In view of this diversity in sedimentological patterns, a series of fundamental questions arise. Have we recognized all significant patterns? And, are all patterns that we recognize significant? These questions underpin both our ability to characterize river deposits and to interpret the singular dynamics that gave rise to individual deposits. Machine learning provides a means of re-analysing data to understand bias and uncertainty within our data domains, and can therefore be used to improve our understanding of ancient and modern rivers from existing datasets. Herein, we apply machine learning techniques to classify sediment core data taken from one of the world's largest rivers: the Río Paraná, Argentina. We apply self-organizing maps for unsupervised clustering of sedimentary structures in the cores. The methods are suited to the analysis of different types of data, including core, borehole geophysics, and outcrops of varying size and quality. Early results illustrate that machine learning classification can: (1) recognize depositional units based on sedimentary structures and their location; and (2) simplify complex patterns of primary sedimentary structures, and present them as sedimentary facies with varying abundance, similarity and degrees of certainty. The success of these initial experiments opens up new opportunities for, for example: (i) automated distinction of depositional environments; (ii) the quantification of vertical and lateral trends in sedimentary deposits; and (iii) an improved interpretation of the generic and singular dynamics that give rise to river deposits. Thus, the results illustrate that machine-learning methods can identify significant patterns from sedimentary cores, including patterns that reveal areas which require further systematic research. Being able to classify sedimentological information in such a semi-automatic way opens new avenues for the analysis of much larger data domains, the interpretation of which would otherwise require vast manual expert effort. Automated detection of sedimentological features from data also enables the quantification of levels of uncertainty within the data domain. As such, machine learning provides a rigorous pathway to integrate uncertainty information into data-driven predictive models, and allows identification of ‘poorly understood’ aspects of river systems.

Abstract Two decades of geological modelling have resulted in the ability to study single-well geological models at a sufficiently high resolution to generate synthetic well test responses from numerical simulations in realistic geological models covering a range of fluvial styles. These 3D subsurface models are useful in aiding our understanding and mapping of the geological variation (as quantified by porosity and permeability contrasts) in the near-wellbore region. The building and analysis of these models enables many workflow steps, from matching well test data to improving history-matching. Well testing also has a key potential role in reservoir characterization for an improved understanding of the near-wellbore subsurface architecture in fluvial systems. Developing an understanding of well test responses from simple through increasingly more complex geological scenarios leads to a realistic, real-life challenge: a well test in a small fluvial reservoir. The geological well testing approach explained here, through a recent fluvial case study in South America, is considered to be useful in improving our understanding of reservoir performance. This approach should lead to more geologically and petrophysically consistent models, and to geologically assisted models that are both more correct and quicker to match to history, and thus, ultimately, to more useful reservoir models. It also allows the testing of a more complex geological model through the well test response.

Abstract Because of climate change, the frequency, intensity and/or duration of extreme weather events such as floods, droughts, storms and extreme temperatures is increasing. These events are often related to loss of property, money and life, especially in poor and developing countries where there is no or poor disaster management due to social and financial difficulties or due to a lack of synergy between the mitigation actions taken. Negative impacts can be reduced and losses can be better handled with proper water management techniques. However, these should not be handled solely with traditional management. The actual problem cannot be over simplified as merely a question of coping with resources availability and demand. Therefore, the present paper aims to summarize advances in weather forecasting and reservoir operation in the Upper São Francisco River, strategic to Brazil because it provides water to the semi-arid region and energy for economically thriving Brazilian regions. Moreover, it discusses challenges, opportunities and improvements needed to implement these advances in the current national integrated water resources management. This is mainly focused on water-related disaster mitigation.

Abstract Hedging is universally recognized as a useful operational practice in surface water reservoirs to temporally redistribute water supplies and thereby avoid large, crippling water shortages. When based on the zones of available water in storage, hedging has traditionally involved a static rationing (i.e. supply to demand) ratio. However, given the usual seasonality of reservoir inflows, it is also possible that hedging could be dynamic with seasonally varying rationing ratios. This study examined the effect of static and dynamic hedging policies on the performance of the Pong reservoir in India during a period of climate change. The results show that the reservoir vulnerability was unacceptably high (≥60%) without hedging and that this vulnerability further deteriorated as the catchment became drier due to projected climate change. The time- and volume-based reliabilities were acceptable. The introduction of static hedging drastically reduced the vulnerability to <25%, although the hedging reduction in the water supplied during normal operational conditions was only 17%. Further analyses with dynamic hedging provided only modest improvements in vulnerability. The significance of this study is its demonstration of the effectiveness of hedging in offsetting the impact of water shortages caused by climate change and the fact that static hedging can match more complex dynamic hedging policies.

Abstract This volume brings together a number of papers from two workshops with the theme, ‘Rain, Rivers, Reservoirs’, which considered the dynamic changes to river systems as part of natural processes, particularly changing climatic conditions. Bringing researchers from two different locations to Brazil and the UK allowed scientists to contribute to and promote, ‘debate on current research…on how the planet works and how we can live sustainably on it’. This volume features a series of papers on the geoscience of modern and ancient rivers from across the world (Brazil, United States, Spain, Argentina, Canada, India and the UK), their evolution through time, their management, their deposits and their engineering, with both subsurface aquifers/hydrocarbon reservoirs (of Carboniferous, Triassic and Cretaceous age) and surface reservoirs considered.