Since their uplift and emergence in the Miocene, the predominantly limestone horst massifs of Crete have been incised by steepland rivers, but Quaternary climate changes have also resulted in alluvial cut-and-fill sequences within the valleys. Distinctive wave-cut notches up to 9 m above present mean sea level around southwestern Crete have been dated, and uplift ascribed to the documented earthquake of AD 365. Ground surveys, geomorphological mapping, sedimentological investigations, and geochronology (OSL, radiocarbon, uraniumseries, and dendrochronology) have enabled detailed reconstruction of the timing and pattern of sedimentation and erosion over the late Holocene. Following uplift, the dominantly-bedrock rivers incised into their uplifted and exposed cemented fan deltas, initiating knickpoint propagation. Given the limited sediment supply to these systems, subsequent climate changes have had little discernible influence on their morphology and sedimentology. In contrast, following uplift, the dominantly-alluvial rivers rapidly incised through their alluviated lower reaches, with knickpoints propagating into bedrock-controlled reaches upstream. Coupled with higher sediment supply, subsequent cut and fill processes have left complex but decipherable terrace records in the lower reaches. The responses of two alluvial fan rivers diverged following uplift. For the first river, uplift exposed a wave cut platform with a lower gradient than the upstream river, leading to the aggradation of a new fan on the exposed area. The second river appears largely unaffected by base level fall, and is instead incising in response to distal truncation of a large alluvial fan at the river mouth. Aggradation in these systems appear to coincide with regional periods of aridity or increasing aridity, during which rainfall tends to be concentrated into fewer, but more intensive precipitation events. Hence, the nature of the responses since AD 365 has been determined by the interplay of factors that are intrinsic to each system and extrinsic effects that correlate primarily with climatic change.

The mineralisation which occurs within the Central Wales Orefield (CWO) is of historical importance, as the area was once one of the major producers of silver in the United Kingdom. In comparison to the other ore districts situated in the British Isles however, surprisingly little research has been undertaken in the CWO in recent years. This thesis redresses this issue by examining, in conjunction with Pb isotope analysis, the geochemical variation in three sulphide minerals (galena, sphalerite and chalcopyrite), collected from six mineralised lodes located in the Afon Clarach catchment; a small river system situated in the northern region of the CWO, north of Aberystwyth. Although the Pb-Ag mines in the CWO have been abandoned for over 100 years, many of these sites continue to have a legacy of pollution, which under the Water Framework Directive (2000/60/EC) now require remediation. By characterising the trace metal and Pb isotope fingerprints of the six mineralised lodes situated in the Afon Clarach catchment, this thesis successfully identifies those mine sites which continue to contaminate the river sediments of the Afon Clarach with trace metals and therefore require remediation. Variations in the Pb isotope ratios and the concentrations of Sb, Tl and Hg identified in the Pb-ore and Tl, In, Fe, Mn and Cu in the Zn-ore collected from the six lodes have successfully differentiated the two periods of mineralisation previously identified in the CWO by Mason (1994) and dated by Fletcher et al. (1993). The Camdwr, Cwmerfyn, Cwmsymlog and Daren Lodes are dominated by the older phase of mineralisation (Group 1) whereas the Hafan Lode is dominated by the younger phase (Group 2). In contrast, the Goginan Lode contains ore minerals which were precipitated during both stages of mineralisation. In addition to differentiating the two periods of mineralisation, subtle variations in the concentrations of Ag, Cd, Co, Cu, Fe, Ni, Pb and Sb in the Pb-ore; Cd, Cu, Ga, Fe, Hg, Ni, Pb, Sb, Tl, In and Zn in the Zn-ore and Cu, Fe, Ga, Hg, In, Pb, Sn and Zn in the Cu-ore differentiate those lodes assigned to the older Group 1. It is possible to use the chemical and isotope signatures of the lodes, to trace the metal contamination, particularly that of Pb, Zn, Cu and Sb, into the river sediments and identify those sites which are continuing to contaminate the Afon Clarach. The priority mine sites identified in the study include Bwlch Mine, Cwmsymlog Mine, Daren Mine and Cwmerfyn Mine, all of which are located along the Nant Silo, one of the four main tributaries of the Afon Clarach. The inclusion of Bwlch and Cwmerfyn Mines in this list is of some concern as these sites have already undergone some remediation work during the early 1990‟s. In addition, mines including Llety-Hen, Willowbank and Pen-y-Cefn are also introducing some metal contamination into the Afon Stewi. The remaining two tributaries of the Afon Clarach (the Bowstreet Brook and the Afon Peithyll) are less affected by metal contamination. The spoil tips located at Mynydd Gorddu Mine, situated on the Bowstreet Brook, however do pose a threat to the local environment with high mean concentrations of Pb (4.21 %), Zn (4.02 %) and Sb (221 g/g) found in the tailings and high concentrations of soluble Zn (7.3 mg/L) found in the water draining the spoil tips.

The hyporheic zone is often de fined as the zone where mixing of surface water and groundwater occurs in shallow sediments beneath and adjacent to rivers. This mixing contributes to create unique biogeochemical conditions that may attenuate contaminants from either upstream surface water or groundwater under gaining and losing conditions. Hyporheic exchange results from di erences in the channel near-bed head as it varies in space in response to interactions between surface flow and bed topography, with the interaction with the water table playing an important role too. Reactions of contaminants in groundwater also dependent on mixing between surface and subsurface water, which occurs in this zone. Therefore, representation of the pro le of upwelling and downwelling exchange between surface water and groundwater have important consequences for contaminant transport. The present work studies nitrogen fate within a restored reach of the River Bure, Norfolk, United Kingdom. To this end, we confront numerical simulations of the hyporheic ow and tracer transport with field measurements of surface flow properties, nearby groundwater table and nitrogen compound concentration. . We numerically model mixing between hyporheic flow paths induced by sediment, bedform, meanders on riverbed, and flow paths of adjacent upwelling of deeper groundwater. Results of the analysis indicate that despite the coarse topographical data and with limited surface water hydraulic data it is possible to defi ne the spatial extent of hyporheic exchange and potential mixing zones for contaminants as a function of residence time. The proposed work has the potential to depict high residence time zones and biogeochemical reactivity in homogeneous and heterogeneous sediments. Furthermore, eldwork analysis shows that in this site the hyporheic zone have a little e ffect on nutrient concentration. In addition, hydraulic modeling results indicate that streambed discharge signi cantly influences hyporheic exchange. Especially, the residence times under average stream discharge conditions are higher than the ones under the high discharge conditions mostly on the part that has ri e - pool morphology. From hydraulic point of view, heterogeneous domain has higher connectivity than the homogeneous ne sand subsurface set. Such that, subsurface flow has tendency to flow through high hydraulic conductivity zones, which is de ned as tunneling eff ect, therefore, low conductivity zones have minor e ect on hyporheic flow. The predictions based on the DaO2 index proves that heterogeneous sediment formations have more aerobic potential, however, prevailing anaerobic conditions occur mostly vicinity of low hydraulic conductivity zones.

A series of geologically, hydrologically and tepographioally similar catchments in cast Anglia was studied. The rivers draining these catchments, the Nar, Wissey, Little Ouse (and tributaries), Lark and Granta are Chalk-fed tributaries of the Great Ouse River. Geologically, the catchments are: underlain by Chalk, partially covered by drift deposits, mainly of glacial origin. It was concluded from an assessment of the general hydrogeological and hydrological regimes of these catchments that the recession of groundwater flow would approximate to an exponential decay curve during dry summers. Subsequently, exponential- groundwater flow recession curves were determined from the hydrograph of total discharge for certain years.

This study investigated the impact of reservoir heterogeneity and physical diffusion/dispersion on low salinity waterflooding (LSW) using detailed numerical simulation. Two different methods for modelling the impact of LSW on relative permeability and hence on recovery were investigated: the salinity threshold model (ECLIPSE and STARS) and the ion exchange model (GEM). These simulators were validated by comparing their predictions with the analytical solution for immediate LSW. Physical diffusion/dispersion were characterized using the dimensionless transverse dispersion number (NTD) which was shown to be a robust measure for determining their impacts on the performance of LSW. The impact of numerical diffusion was evaluated for a range of grid resolutions and a correlation developed for estimating the maximum physical longitudinal dispersion that can be captured for a given grid resolution. The impact of transverse numerical diffusion was found to be very small. On laboratory scales, it was found that diffusion improves the oil recovery in layered high net-to-gross models but reduces the effectiveness of continuous LSW in models containing a thick shale filled with connate water. On the reservoir scale, the effect of dispersion on LSW was found to be minor compared with reservoir heterogeneity. The adverse effect of an aquifer was found to be most significant during the production of the connate water bank. If low salinity water is injected immediately as a slug, it was found that the best slug size is around 0.4-0.6 PV assuming a total water injection of 1 PV. If it is injected after a conventional water flood then the slug size increases to 1.3 PV assuming a total water injection of 2 PV. Finally, an analytical pseudoization method was proposed to upscale LSW by modifying Hearn’s method for layered reservoirs to include the connate water bank. This method was shown to give improved predictions over those obtained by the original Hearn’s method when compared using a 2D layered model.

Most rocks contain magnetic minerals that acquire a natural remanent magnetization (NRM) in the direction of the geomagnetic field during their formation. Floods may quarry, transport and rotate boulders such that their NRM will subsequently be randomly aligned. The magnetic minerals then gradually acquire a viscous remanent magnetization (VRM) at ambient temperatures in the direction of the ambient field that partially overprints the original NRM. According to Néel's (1949) theory of fine magnetic particles, the demagnetization temperature of a VRM is a function of acquisition time and can be used to date the movement of the rock and, hence, the flood. No generally accepted standard method of VRM dating exists yet. In this thesis, a theory of VRM acquisition is rigorously derived and experimentally tested, including heating/cooling rate effects, temperaturedependence of the attempt time, and the effect of mixtures of magnetic minerals. A protocol for VRM flood dating based on continuous thermal demagnetization (CTD) of flood boulders is proposed and evaluated on five cases of known ages: three jökulhlaups in Iceland (Sólheimajökull, Kotarjökull and Markarfljot), a storm flood deposit in Scotland, and a tsunami in Cape Verde. The protocol encompasses sampling procedure, CTD of the NRM, magnetic viscosity experiments, criteria for sample selection and a full statistical treatment of the obtained age estimates and uncertainties. Two Icelandic dating attempts were successful, while the remaining three attempts were unsuccessful, but were clearly identifed as such. In the two successful cases gave a good agreement with known ages of 72 years (error limits 11-360 years) versus a known age of 155 years for the Sólheimajökull flood and 290 years (error limits 80-2300 years) versus a known age of 288 years for the Kotarjökull flood. This suggests that CTD of VRMs can be a useful order-of-magnitude tool for flood dating.

The Amazon hydrological cycle has intensified since approximately 1990, and yet long-term meteorological data from the region are limited, making it difficult to determine the cause of current variability. Proxy records can be used to reconstruct past climate, thus providing useful historical context for recent changes. This thesis focuses on the climate insights that can be gained from oxygen isotopes in tree rings (δ18OTR). The consistency of annual ring formation was tested first, as this is an important prerequisite for constructing a well-dated proxy record. Cedrela trees were found to form annual rings across most of the species’ natural range, but biannual rings in Suriname (Chapter 3). Next, new δ18OTR records were developed from Cedrela and seven other tree species from northern Bolivia. δ18OTR signals were shown to correlate between different species, and between sites large distances apart ( < 1000 km), indicating a large-scale environmental control on δ18OTR (Chapter 4). Following this, atmospheric back-trajectory modelling and basin-scale vapour transport analysis were used to confirm that rainout of heavy isotopes during moisture transport across the continent is the primary control on interannual δ18OTR signals in the western Amazon (Chapter 5). Finally, new Cedrela δ18OTR chronologies from Ecuador and Bolivia were developed. These records show an increase in δ18OTR from the early 1800s until approximately 1950, indicating a change in hydrological functioning over this period, with a reversal in the trend over the last 1–2 decades. The increase is most likely driven by a reduction in the fraction of incoming water vapour that rains out over the Amazon, which could be caused by a reduction in precipitation, or an increase in the volume of imported vapour. Overall, these results provide evidence for long-term changes in Amazon hydrology over the past 200 years, and make an important contribution to the field of tropical dendroclimatology.

The thermal characteristics of the hyporheic zone reflect complex relationships between hydrological, climatological, sedimentological and topographical parameters that occur over a range of spatial and temporal scales. This thesis defines hyporheic temperature profiles, focusing on the influence of meteorology, hydrology and geomorphology; and examines the ecological implications. A pilot study, using a chemical technique to determine temperature profiles of average monthly water temperature to a depth of up to 85 cm in the River Wissey, Norfolk showed that substratum characteristics have a significant influence upon hyporheic temperature patterns. A strong seasonal pattern was defined at all sites with hyporheic temperatures being relatively warm in winter and cool in summer. Temperature ranges within the hyporheic were decreased (4.6-7.7 °C) compared with those of surface waters (10 and 10.9 °C) between February and October 1992. Miniature dataloggers provided high resolution temperature information on the regulated River Blithe, Staffordshire. Data demonstrated that riffle topography produced distinct longitudinal hyporheic temperature patterns in relation to exchanges of channel and groundwater within the hyporheic zone. Riffle heads were 2.26 °C warmer and 1.29 °C cooler than riffle tails hi July and December 1994. Spatial and temporal changes in sedimentological and hydrological factors disrupted the longitudinal pattern of channel and groundwater interactions within the river bed. Increased channel discharge during January and February 1995 decreased hyporheic temperatures by up to 5 °C in areas previously influenced by warmer groundwater. Detailed hydrometeorological monitoring comparing a riffle-pool-riffle sequence highlighted the significance of the river bed as an energy store/source with up to 24% of daily energy exchanges occurring at the channel bed. The magnitude of energy transfers to and from the river bed displayed a high degree of spatial and temporal variability. The thesis concludes with a discussion of the significance of the results and the implications for ecological processes, flow regulation and abstraction, and climate change.

Several numerical and hydraulic aspects of river modelling are studied in two parts. Part I deals with the investigation of the flow characteristics in the lateral and vertical directions. The concepts and assumptions adopted in a theoretical model for the description of turbulent flow are addressed. Certain experimentally derived coefficients required by the model are investigated using the data from the UK SERC-FCF. It is followed by the implementation of a finite element computer model called RFMFEM to obtain a solution to the depth averaged momentum equation. The model can describe the lateral distributions of depth mean velocity and Reynolds shear stress, and the local boundary shear stress in channels of any cross sectional shape. Benchmarking and validation of the model is attained by comparisons with an analytical solution and experimental data. Through the lateral integration of the flow to give the discharge, the model may also predict the stage-discharge relationship. Likewise it is utilised in sediment transport analysis in open channels. Part II addresses the study of river engineering related to the unsteady changes in the longitudinal direction. Hence the theory of flood routing is briefly discussed. Simplified models based on the diffusion analogy are adopted for one-dimensional flood routing analysis. The finite element method is applied in the formulation of a variable parameter diffusion model called RFRFEM for the solution to the nonlinear convection-diffusion equation. A detailed study of the routing parameters is performed based on the prediction of the rating curve. Model validation is attained through comparisons with,, both analytical solutions for simplified cases and systematic series of flood routing benchmark tests for inbank flow. It ultimately deals with the joint application of the turbulence and routing models to analyse overbank flood routing in natural rivers.

Sediment transport and morphological change can play an important role during extreme coastal flood events. In this thesis, a set of 2-D shallow water-sediment equations is derived that incorporate suspended sediment, bedload transport and bed morphological evolution. A balanced stage-discharge hyperbolic formulation is adopted, which is suitable for complex shallow flows such as large-scale inundation over natural terrain. The 2-D shallow water-sediment equations are solved using a second-order Godunov-type approximate Riemann solver on dynamically adaptive quad tree grids. The numerical model is capable of simulating large-scale flood inundation over complex terrain. A number of test cases have been presented to validate the numerical model. The thesis also presents results from wave overtopping experiments of a scale model of the Anchorsholme seawall, carried out at HR Wallingford. The measurements of water surface elevation time histories from focused and irregular wave tests should be useful for validating numerical models of wave overtopping. The 2D shallow water model has also been applied to simulate the coastal flood inundation of Walcott, Norfolk. Considerable care has been taken to include building configurations. The results reproduce the pattern of flooding experienced at Walcott in November 2007, and demonstrate the importance of the street layout in channelling flood water. A Lagrangian particle tracking model is also presented for predicting the near bed saltation of sediment particles. In order to achieve higher order of accuracy, a fourthorder Runge-Kutta scheme is used for time-integrating the equations of motion of a spherical particle. Particle saltation over a flat bed and over a uniform bed comprised of hemispherical particles are simulated in unidirectional flow. The nonlinear dynamics of the particle saltation is investigated, and both regular and chaotic motions are observed. The Lagrangian particle saltation model has also been extended to simulate sediment particle transport in tidal flow.