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The exploitation of river systems for power and navigation has commonly been achieved through the installation of a variety of in-channel obstacles of which weirs in Britain are amongst the most common. In the UK, the historic value of many of these features is recognised by planning designations and protection more commonly associated with historic buildings and other major monuments. Their construction, particularly in the north and west of Britain, has often been associated with industries such as textiles, chemicals, and mining, which have polluted waterways with heavy metals and other contaminants. The construction of weirs altered local channel gradients resulting in sedimentation upstream with the potential as well for elevated levels of contamination in sediments deposited there. For centuries these weirs have remained largely undisturbed, but as a result of the growth in hydropower and the drive to improve water quality under the European Union's Water Framework Directive, these structures are under increasing pressure to be modified or removed altogether. At present, weir modifications appear to be considered largely on an individual basis, with little focus on the wider impacts this might have on valley floor environments. Using a numerical modelling approach, this paper simulates the removal of major weirs along a 24-km stretch of the river Derwent, Derbyshire, UK, designated as a UNESCO World Heritage Site. The results suggest that although removal would not result in significant changes to the valley morphology, localised erosion would occur upstream of structures as the river readjusts its base level to new boundary conditions. Modelling indicates that sediment would also be evacuated away from the study area. In the context of the Derwent valley, this raises the potential for the remobilisation of contaminants (legacy sediments) within the wider floodplain system, which could have detrimental, long-term health and environmental implications for the river system. Worldwide, rivers have a common association with industry – being the focus of settlement and development since the earliest civilisations with channel engineering a common practice. Therefore, the conceptual issues raised by this study have global resonance and are particularly important where heritage protection is less robust and structures can be removed with little consideration of the environmental consequences. [ABSTRACT FROM AUTHOR]

Abstract: The last decade has witnessed the development of a series of cellular models that simulate the processes operating within river channels and drive their geomorphic evolution. Their proliferation can be partly attributed to the relative simplicity of cellular models and their ability to address some of the shortcomings of other numerical models. By using relaxed interpretations of the equations determining fluid flow, cellular models allow rapid solutions of water depths and velocities. These can then be used to drive (usually) conventional sediment transport relations to determine erosion and deposition and alter the channel form. The key advance of using these physically based yet simplified approaches is that they allow us to apply models to a range of spatial scales (1–100 km2) and time periods (1–100 years) that are especially relevant to contemporary management and fluvial studies. However, these approaches are not without their limitations and technical problems. This paper reviews the findings of nearly 10 years of research into modelling fluvial systems with cellular techniques, principally focusing on improvements in routing water and how fluvial erosion and deposition (including lateral erosion) are represented. These ideas are illustrated using sample simulations of the River Teifi, Wales. A detailed case study is then presented, demonstrating how cellular models can explore the interactions between vegetation and the morphological dynamics of the braided Waitaki River, New Zealand. Finally, difficulties associated with model validation and the problems, prospects and future issues important to the further development and application of these cellular fluvial models are outlined. [Copyright &y& Elsevier]

Abstract: The CAESAR (Cellular Automaton Evolutionary Slope And River) model is used to demonstrate significant differences in coarse sediment transfer and alluviation in medium sized catchments when responding to identical Holocene environmental changes. Simulations for four U.K. basins (the Rivers Swale, Ure, Nidd and Wharfe) shows that catchment response, driven by climate and conditioned by land cover changes, is synchronous but varies in magnitude. There are bursts of sediment transfer activity, generally of rapid removal but with some sediment accumulation ‘spikes’, with longer periods of slow removal or accumulation of sediment in different valley reaches. Within catchments, reach sensitivity to environmental change varies considerably: some periods are only recorded in some reaches, whilst higher potential sensitivity typically occurs in the piedmont areas of the catchments modelled here. These differential responses appear to be highly non-linear and may relate to the passage of sediment waves, by variable local sediment storage and availability, and by large- and small-scale thresholds for sediment transfer within each catchment. Differential response has major implications for modelling fluvial systems and the interpretation of field data. Model results are compared with the record of dated alluvial deposits in the modelled catchments. [Copyright &y& Elsevier]

A significant issue for the application of numerical Landscape Evolution Models (LEMs) is their calibration/parameterisation and validation. LEMs are now at the stage of development where if calibrated, they can provide meaningful and useful results. However, before use, each LEM requires a set of data and parameter values for it to run reliably and most importantly produce results with some measure of precision and accuracy. This calibration/validation process is largely carried out using parameter values determined from present day, or recent surface conditions which are themselves product of much longer-term geology-soil-climate-vegetation interactions. Here we examine the reliability of an LEM to predict catchment form over geological time (500,000 years) for a potential rehabilitated mine landform using defensible parameters derived from field plots. The findings demonstrate that there is no equifinality in landscape form with different parameter sets producing geomorphically and hydrologically unique landscapes throughout their entire evolution. This shows that parameterisation does matter over geological time scales. However, for shorter time scales (< 10,000 years) the geomorphic differences in hillslope form are minimal as described by the hypsometric curve, area–slope and cumulative area distribution, yet there are large differences in sediment output. Therefore, obtaining reliable and defensible parameters for input to LEMs is essential. [ABSTRACT FROM AUTHOR]

An important part of planning for the rehabilitation of a mine site is the design of stable final landforms for waste rock dumps or spoil piles. Whilst able to be assessed over the short-term (years to decades), the longer term behaviour (centuries to millennia) of such landscapes is not within any meaningful human time frame of observation. Predictive numerical models, therefore, form an important tool with which current landscape behaviour and longer term trajectory can be assessed. However, an important issue associated with the use of models is the ability to assess the reliability and accuracy of the model. Here the SIBERIA and CAESAR-Lisflood Landscape Evolution Models (LEMs) are used to simulate and assess the geomorphic stability of a conceptual rehabilitated landform of the Ranger uranium mine in the Northern Territory, Australia, for a simulated period of up to 1000 years. Utilising both models in this study enabled an independent assessment of likely landscape processes and evolution as well as each model. Results show that SIBERIA and CAESAR-Lisflood produce erosion rates and patterns that are broadly similar. At millennial time scales, short-term processes such as gullying appear to be the dominant erosion features in the proposed landforms and may produce substantial erosion in terms of size and amount of hillslope material eroded and transported downslope. Vegetation was found to have a major effect on the erosion potential of the landform surface. Overall both models produce very similar results. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes 20th century climate and human impacts on terrestrial and fluvial systems in the Dabie Mountains, Anhui Province, China, based on analyses of four types of information. Analyses of particle size, mineral magnetism, organic carbon, nitrogen and phosphorus in a sediment core taken from the Longhekou reservoir, built in 1958 AD in the upper reaches of Hangbu River, provide an ∼45 year record of fluvial responses, while monitored meteorological and hydrological data provide records of climate and river discharge. Census data compiled for the local Shucheng County provide records of population and land use, complemented with analyses of satellite images. The Xiaotian river delivers over 65% of the total water and silt to the reservoir. Analyses indicate that the fluvial regime tracks the monsoon climate over seasonal timescales, but human activities have a strongly mediating effect on sediment supply, sediment delivery and, to a lesser extent, runoff over longer timescales. Notable periods of human impact on erosion include the Great Leap Forward (1958–1960) and Great Cultural Revolution (1966–1976). A rising trend in precipitation and new land use changes at the present time may be leading to an enhanced flood risk. [Copyright &y& Elsevier]

Abstract: As the result of current and historical metal mining, river channels and floodplains in many parts of the world have become contaminated by metal-rich waste in concentrations that may pose a hazard to human livelihoods and sustainable development. Environmental and human health impacts commonly arise because of the prolonged residence time of heavy metals in river sediments and alluvial soils and their bioaccumulatory nature in plants and animals. This paper considers how an understanding of the processes of sediment-associated metal dispersion in rivers, and the space and timescales over which they operate, can be used in a practical way to help river basin managers more effectively control and remediate catchments affected by current and historical metal mining. A geomorphological approach to the management of rivers contaminated by metals is outlined and four emerging research themes are highlighted and critically reviewed. These are: (1) response and recovery of river systems following the failures of major tailings dams; (2) effects of flooding on river contamination and the sustainable use of floodplains; (3) new developments in isotopic fingerprinting, remote sensing and numerical modelling for identifying the sources of contaminant metals and for mapping the spatial distribution of contaminants in river channels and floodplains; and (4) current approaches to the remediation of river basins affected by mining, appraised in light of the European Union''s Water Framework Directive (2000/60/EC). Future opportunities for geomorphologically-based assessments of mining-affected catchments are also identified. [Copyright &y& Elsevier]