Links between variables such as soil maturity, f1owpaths, water residence time, carbon export and weathering rates need to be further established in order to evaluate the effects of future climatic change on the hydrology and carbon economy of subarctic catchments. Recent studies on post-deglaciation landscape development in the Alaskan Glacier Bay area have suggested that the importance of 1) deep ground water flowpaths and 2) carbonate weathering, decrease with time since deglaciation as soil pans form, vegetation cover increases and soils become depleted in reactive minerals. We present here, detailed water and nutrient mass balances for three subarctic micro-catchments (<1 km2) located along a landscape maturity gradient in the Abisko area in northern Sweden. Stream- and soil water, precipitation and snowpacks were sampled frequently. Results include evidence of changing flowpath routing, DOC character and concentration of DIC and weathering products along this gradient. A conceptual model was suggested for long-term hydrological change in the Scandinavian mountainious area where the geomorphological setting causes an effective gradient in such related biogeochemical variables. The importance of a slow ground water flowpath increased with landscape maturity. It is suggested that this was mainly due to geomorphology; uniform soil conditions after deglaciation which are applicable for Alaskan catchments are replaced by erosion and transport of sediment from the top to the bottom of valleys. Hydrologic feedback on climatic change will depend upon the ultimate down-stream fate of organic and inorganic carbon but this study suggests that uptake of atmospheric CO2 in weathering reactions is an important negative feedback, especially in the flat bottom valleys with deep soils, dominated by a slow groundwater flowpath. Further, results provide evidence that a large part of the carbon input to high-altitude catchments is derived from microbial production within snowpacks. This input had a magnitude similar to overall loss of organic carbon, suggesting that snow melt carbon input significantly contributes to microbial and weathering processes within the soil of these systems.

Robust numerical models are an essential tool for informing ood and water management and policy around the world. Physically-based hydrological models have traditionally not been used for such applications due to prohibitively large data, time and computational resource requirements. Given recent advances in computing power and data availability, this study creates, for the rst time, a robust, physically-based hydrological modelling system for Great Britain using the SHETRAN model and national datasets. Such a model has several advantages over less complex systems. Firstly, compared with conceptual models, a national physically-based model is more readily applicable to ungauged catchments, in which hydrological predictions are also required. Secondly, the results of a physically-based system may be more robust under changing conditions such as climate and land cover, as physical processes and relationships are explicitly accounted for. Finally, a fully integrated surface and subsurface model such as SHETRAN o ers a wider range of applications compared with simpler schemes, such as assessments of groundwater resources, sediment transport and ooding from multiple sources. In order to develop a national modelling system based on SHETRAN, a large array of data for the whole of Great Britain and the period 1960-2006 has been integrated into a framework that features a new, user-friendly graphical interface, which extracts and prepares the data required for a SHETRAN simulation of any catchment in Great Britain. This has vastly reduced the time it takes to set up and run a model from months to seconds. Structural changes have also been incorporated into SHETRAN to better represent lakes, handle pits in elevation data and accept gridded meteorological inputs. 306 catchments spanning Great Britain were then modelled using this system. The standard con guration of this system performs satisfactorily (NSE > 0.5) for 72% of catchments and well (NSE > 0.7) for 48%. Many of the remaining 28% of catchments that performed relatively poorly (NSE < 0.5) are located in the chalk in the south east of England. As such, the British Geological Survey 3D geology model for Great Britain (GB3D) has been incorporated for the rst time in any hydrological model to pave the way for improvements to be made to simulations of catchments with important groundwater regimes. This coupling has involved development i of software to allow for easy incorporation of geological information into SHETRAN for any model setup. The addition of more realistic subsurface representation following this approach is shown to greatly improve model performance in areas dominated by groundwater processes. The sensitivity of the modelling system to key inputs and parameters was tested, particularly with respect to the distribution and rates of rainfall and potential evapotranspiration. As part of this, a new national dataset of gridded hourly rainfall was created by disaggregating the 5km UK Climate Projections 2009 (UKCP09) gridded daily rainfall product with partially quality controlled hourly rain gauge data from over 1300 observation stations across the country. Of the sensitivity tests undertaken, the largest improvements in model performance were seen when this hourly gridded rainfall dataset was combined with potential evapotranspiration disaggregated to hourly intervals, with 61% of catchments showing an increase in NSE as a result of more realistic sub-daily meteorological forcing. Additional sensitivity analysis revealed that the slight over-estimation of runo using the initial model con guration which has a median water balance bias of 5% was reduced in 62% of catchments by increasing daily potential evapotranspiration rates by 5%. Similarly, model performance was also found to improve by universally decreasing rainfall rates slightly, which together indicate the possibility of slight under-estimation of potential evapotranspiration derived from available data. In addition to extensive sensitivity testing, the national modelling system for Great Britain has also been coupled with the UKCP09 spatial weather generator to demonstrate the capability of the system to conduct climate change impact assessments. A set of 100 simulations for each of 20 representative catchments across the country were processed for a medium emissions scenario in the 2050s, in order to establish and demonstrate the methodology for conducting such an assessment. The results of these initial simulations suggest that higher potential evapotranspiration rates, combined with modest increases in rainfall under this climate change projection, lead to a general decrease in mean annual river ows. Changes in mean annual ow across the country vary between -26% to +8%, with the biggest reductions in ow found in the south of England and modest increases in runo across Scotland. This work represents a step-change in how the physically-based hydrological model SHETRAN can be used. Not only has this project made SHETRAN much easier to use on its own, but the model can now also be used in conjunction with external applications such as the UKCP09 spatial weather generator and GB3D. This means that the modelling system has great potential to be used as a resource at national, regional and local scales in an array of di erent applications, including climate change impact assessments, land cover change studies and integrated assessments of groundwater and surface water resources.

Secondary polymer flooding can significantly improve oil recovery over that obtained by waterflooding. This is achieved principally by improving the water-oil mobility ratio and thus reducing channelling. There are, however, several polymer-specific mechanisms (such as adsorption, mixing, permeability reduction, non-Newtonian flows) that make it more difficult to model numerically compared with waterflooding. Upscaling reservoir properties for reservoir simulation is one of the most important steps in the workflow for building robust dynamic simulation models. It is necessary to reduce computing time and resources when it is not possible to run multiple high resolution models (e.g. as in evaluating the impact of geological uncertainty). This is normally achieved by modifying the inputs to reservoir simulation to represent the influence of sub-grid block heterogeneities on large scale flow and also to compensate for numerical dispersion. At the time of writing there are no accepted methods for upscaling polymer flooding. This study investigates the possibility of creating a methodology to upscale the permeability, the relative permeability, and polymer properties such as adsorption and non-Newtonian flow index. This helps to better represent the secondary polymer flood process by accounting for sub-grid block heterogeneity and compensate for numerical dispersion. The proposed methodology consists of four stages: First, the absolute permeability is upscaled using any of the available upscaling techniques in the literature. This will allow representing the effects of geological heterogeneity on pressure. Second, the effective relative permeability curves are calculated to represent these heterogeneities on the flood front conformance. Third, traditional dynamic pseudo methods are used to compensate for numerical dispersion. Finally, upscale polymer properties to better represent the average polymer concentration distribution in the reservoir. An experimental design has been conducted to identify which polymer property have the most effect in polymer flood simulation. Both the experimental design and the proposed methodology have been demonstrated on a series of 1D and 2D runs with various heterogeneity levels. An alternative method is also presented which is based on volume averaging of properties. This is similar to the pseudoization techniques used for the upscaling the relative permeability with the addition of pseudoizing both adsorption and polymer viscosity in order to accurately represent track the polymer front in the coarse grid model. this method is also tested using several 1D and 2D cases with different permeability distributions.

Surface ponds play a key role in transferring atmospheric energy to the ice for debris-covered glaciers, but as the spatial and temporal distribution of ponds is not well documented, their effect on glacier ablation is unknown. This thesis uses remote sensing and field methods to assess the distribution of supraglacial ponds in the Langtang Valley of Nepal, then develops and applies numerical models of pond surface energy balance to determine energy receipts at the pond, glacier, and basin scales. 172 Landsat TM/ETM+ scenes are analysed to identify thawed supraglacial ponds for the debris-covered tongues of five glaciers for the period 1999-2013. There is high variability in the incidence of ponding between glaciers, and ponds are most frequent in zones of low surface gradient and velocity. The ponds show a pronounced seasonality, appearing rapidly in the pre-monsoon as snow melts, reaching a peak area in the monsoon of about 2% of the debris-covered area, then declining in the post-monsoon as ponds drain or freeze. The satellite observations are supplemented by diverse field observations on Lirung Glacier in the Langtang Valley made in 2013 and 2014, confirming that overall pond area is markedly higher in the pre-monsoon than post-monsoon. Four ponds are observed in detail showing pond drainage, stability, and growth. The thesis then advances efforts to develop a model of mass and energy balance for supraglacial ponds, using field data from a small pond on Lirung Glacier. Sensitivity testing is performed for several key parameters and alternative melt algorithms. The pond acts as a significant recipient of energy, and participates in the glacier’s local hydrologic system during the monsoon. The majority of absorbed energy leaves the pond via englacial conduits, delivering sufficient energy to melt 2612 m3 of ice (~5.3 m ablation for the pond area). Energy receipts for all Lirung Glacier ponds for 2014 are then determined, using the full model and simpler approaches based on data availability. The partition of absorbed energy between pond-proximal and englacial melt is inconsistent between ponds, and the shortwave energy balance alone is not adequate to represent pond energy absorption. The model results suggest that ponds absorbed sufficient energy to account for ~10% of Lirung Glacier’s ablation in 2014.Finally, a simplified pond surface energy-balance model is applied to assess pond energy absorption for the entire Langtang catchment, using local meteorological data for 2013 and mean monthly pond distributions from the Landsat observations. Supraglacial ponds are found to absorb sufficient atmospheric energy to account for 5-16% (mean ~12%) of the debris-covered area’s volume loss in 2013 (equivalent to 0.11 m thinning for this area). Less absorption occurs in the pre-monsoon and post-monsoon than in the monsoon due to decreased latent heat exchange. Altitude is an additional control, but seasonal surface energy balance remains positive at the ELA of 5400 m. This research suggests that due to the efficiency of supraglacial ponds as vectors of atmospheric energy to the glaciers’ interior, they may account for a considerable portion of the debris-covered area’s ablation (~10%) in spite of their low aerial coverage (1-2%), and ponds must be accounted for in studies of debris-covered glacier ablation and evolution.

Thermal conditions in river water are of importance as they influence water quality, chemical processes, ecology, and biological conditions in rivers. In meltwater streams draining from Alpine glaciers, temperatures measured close to glacier termini show strong diurnal variation and paradoxical seasonal variation, being cool when energy availability is greatest. This thesis aims to describe temporal variations of water temperatures in five glacier-fed streams, which drain catchments of varying percentage glacierisation, in the Swiss Alps. Contrasting patterns of ablation season meltwater temperatures, and influences of basin characteristics and river channel morphology on water temperature are assessed. Relationships between solar radiation, air temperature, and water temperature were also investigated. A model was developed in order to estimate the impact of glacier recession on meltwater temperature. Observed temperatures in the Findelenbach during one ablation season were used to calibrate the model, which was subsequently validated on other years. Paucity of data in mountainous regions necessitated a model that required few measured variables to be developed. Distinctive seasonal water temperature regime was identified for larger rivers which drain relatively steep catchments, with substantial basin ice coverage. Such a regime is not replicated in streams draining smaller glaciers with lower gradients. Patterns in diurnal ranges of temperature in rivers draining large glaciers have been identified, temperature ranges reducing during days with high radiation and rising riverflows. Stream surface area was found to be the main catchment characteristic influencing temperature in glacier-fed rivers. Measured stream albedo values suggest that surface reflectivity is unlikely to be a major control on water temperature. Stream temperatures simulated by the model demonstrate high fidelity to those measured in the field. The temperature of glacier-fed streams will increase as climate warms as the distance over which heating can occur will lengthen as glaciers retreat, despite volume of flow being augmented by the deglaciation discharge dividend.

No description available.

Chalk streams drain areas of outcropping chalk and receive a significant proportion of their discharge from the substantial underground aquifers found within chalk geological formations. Chalk streams flow through open countryside, have high nutrient status, clear waters and a stable hydrological regime and these conditions promote the development of a substantial macrophyte community typically dominated by Ranunculus spp. These streams also support large populations of blackfly larvae which are found attached to the surfaces of submerged macrophytes. The larvae feed by using paired cephalic head fans to intercept particles passing in the water column. Blackfly larvae have a low assimilation efficiency and therefore a significant proportion of the ingested material is egested as faecal pellets. Studies have revealed these faecal pellets to be the dominant particles in the suspended load in some systems and this has important implications for particle transport and fate. This study investigated how blackfly larvae alter the size range of particles within streams through the production of faecal pellets and the presence and temporal dynamics of these faecal pellets within two chalk streams in Southern England. Experiments also established the factors that determine the fate of blackfly faecal pellets by investigating the interaction between the annual growth cycle of macrophytes and the accumulation and transport of faecal pellets the controls on the transport of faecal pellets, relating to physical variations in the pellet itself and the factors that influence the decomposition of this material within the stream.

The Great Karoo spans the north-central part of South Africa at a major climatic boundary. The characteristics, spatial patterns and drivers of river channel response to Late Quaternary climate changes in the Sneeuberg, South Africa remain unclear due to the discontinuous alluvial stratigraphic record and the lack of dated palaeoclimatic archives. Dendritic channel networks in the upper Sundays River are deeply incised exposing terrace fills of varying thickness (2-6 m), extent (1 - > 10km) and pedogenic overprinting. Channels exhibit 'stepped' long profiles where resistant rock strata (dolerite, sandstone) cross valley floors, but are now partially or completely breached. DGPS surveys, sediment logging, mineral magnetic measurements and radiometric dating (OSL and 14C) were used to determine the source, age structure and depositional process of valley fills and ascribe intensity of pedogenic overprinting. A conceptual model of terrace development in relation to changing conditions of connectivity was tested. First order streams were desensitised to late Quaternary base level changes downstream due to the blocking effect of two barriers, with localised autogenic 'cut and fill'. Contrastingly, the continuity of 4 fill terraces over incised barriers in 2nd-4th order tributaries indicate relatively high sensitivity to post-LGM climatic change. However, deposition of alluvium (T2) inset within periglacial deposits (T1) was partly a complex response to re-connection of the channel network with deep upland colluvial stores resulting in the valleys becoming choked with sediment. This caused a rise in groundwater and formation of extensive (> 10 km2) rootmats on valley floors, restricting depth of subsequent channel entrenchment (T3/T4). This study presents one of the first attempts in South Africa to test and explain terrace genesis and correlation using existing conceptual models for sediment connectivity. The relative roles of periglaciation and fluvial activity are shown to be key influences on dynamics of Quaternary sedimentation, pedogenesis and erosion and help to explain how sediments can be preserved over long periods (104 years) in catchments subject to base level fall.

Despite the recognition of fluvial geomorphology as an important scientific input to the management of river catchments, limited knowledge exchange has occurred between scientific researchers and river management stakeholders. An example of this issue can be found within the limited uptake of numerical models of sediment dynamics by river management stakeholders. The uptake of these models is important as they have the potential to demonstrate how, at the catchment-scale, the impacts of management strategies of land-use change affect sediment dynamics and resulting channel quality. This thesis describes and evaluates a new transdisciplinary approach which involves river management stakeholders in an iterative and reflexive participatory modelling process. This approach aimed to create an environment for knowledge exchange and social learning between the stakeholders and the research team in the process of co-constructing a catchment-scale sediment dynamics model. This process involved four groups of UK river catchment stakeholders, who were involved in several stages of the participatory modelling process including: requirements analysis, model design, model development, model assessment, and an evaluation of the process. Stakeholders input into a number of aspects of the modelling process, such as: data requirements, user interface, modelled processes, model assumptions, model applications, and model outputs. The findings from the participatory modelling process provided valuable insights into the requirements of river management practitioners, and identified a number of gaps in knowledge for future research. The process evaluation critically assessed the participatory modelling process, and the solutions implemented to address the participatory issues identified in the literature. The findings revealed a number of methodological contributions including methods for ensuring participation is meaningful, and knowledge exchange and social learning occur. The usefulness and future of the developed model are also established through the model assessment. The conclusion reflects on these findings, identifies the implications for fluvial geomorphology and participatory modelling, and presents topics for future research.

No description available.