River Terrace Deposits Research Articles

Amino acid dating of Pleistocene mammalian enamel from the River Thames terrace sequence: a multi-taxon approach

Amino acid geochronology can provide effective relative dating frameworks for the Pleistocene and has enabled correlation of terrestrial deposits to the global climatic fluctuations described by the marine oxygen isotope record. Using methods developed for the analysis of intra-crystalline amino acids in tooth enamel, we aimed to construct an enamel-based amino acid geochronology for the terrace deposits in the valley of the River Thames in southern Britain using different mammalian taxonomic groups: elephant, horse and bison. To achieve this, chiral amino acid analysis was applied to 58 elephantid, 21 horse and 15 bison teeth from 10 horizons in the Upper Thames Valley, three in the Lower Thames Valley and one from a Thames tributary in the Lea Valley. We evaluate differences in the rates of amino acid breakdown between the taxa and establish which species are similar enough to enable comparison for relative dating purposes. The relative dating of the river terrace deposits is in good agreement with the terrace stratigraphy, biostratigraphy, and other independent estimates of age for all three taxonomic groups. These frameworks demonstrate the potential of enamel-based amino acid geochronologies for relative dating of Middle–Late Pleistocene deposits in the UK, and establish an aminostratigraphic framework from which the dating of other tooth material can be refined. Enamel offers an opportunity to evaluate the age of sites where shell material is absent or poorly preserved. It can also, crucially, provide direct relative dating of mammalian fossils, which are often the focus of study in terms of their evolution, distributional changes or extinction. Direct dating negates the risk that the mammal fossils themselves might be reworked, or of different ages to shell, sediments or other dated material in the same deposits; it also enables archived samples with insecure provenance (e.g. from early 17th-19th century collections) to be directly dated.

The Quaternary sequence of the Nahr el Kebir, NW Syria: An important repository for evidence of Palaeolithic occupation and landscape evolution in the eastern Mediterranean

The third largest river in Syria, the Nahr el Kebir has a well-preserved record of river-terrace deposits that have produced substantial Palaeolithic artefact assemblages both from within the terrace deposits and from the land surfaces above and around them. At the Mediterranean coastline, the fluvial gravels interdigitate with raised shoreline terrace deposits, providing an insight into the temporal and climatic relations of both of these important geomorphological and morphostratigraphical archives, as well as their relationship with each other. New research is reported here on the Pleistocene geology and geomorphology of the Nahr el Kebir and the associated Palaeolithic archaeology, the latter having been reinterpreted based on reassessment of museum collections arising from earlier detailed work. Field visits revealed an additional, hitherto unrecognized low-level river terrace, whereas one of the previously recognized Palaeolithic levels can be shown to coincide with slope deposits that armour hilltops rather than representing a genuine fluvial formation. The new understanding of these geomorphological and sedimentary archives supports ideas that this corner of the Mediterranean has experienced unusually rapid uplift during the recent Quaternary, as a result of which the local rivers, including the Kebir, have deepened their valleys rapidly. Consequently, only the recent part of the Quaternary is recorded in the Kebir system and the ages envisaged previously for the terrace deposits and the Palaeolithic artefact assemblages were considerable overestimates in many cases, a finding that has significance for their correlation with those from the wider region. Reassessment of the Palaeolithic archaeology suggests a settlement history initially dominated by groups using handaxes, alongside simple core working (0.5–0.3 Ma), followed by a major change with the appearance of Levallois core working alongside handaxes, marking the transition to the early Middle Palaeolithic.

Reinforcement of piling platforms with geogrids over dewatered docks with very soft soils: Wood Wharf, London

Wood Wharf is a major redevelopment of 23 acres designed to provide residential and office buildings as well as public spaces for shops, restaurants, parks and community uses. The development is located on the Isle of Dogs, Canary Wharf, London. This paper describes the design and results of the piling mats required to construct the buildings in the area of the South Dock, where 14,000m2 of land had to be reclaimed. Cofferdams were installed to create a watertight retaining structure to facilitate dry construction methods in the reclaimed area behind the new quay wall. To construct the different buildings, CFA and LDA piles between 8m to 34m deep were installed for the foundations. The soil profile primarily comprised Made Ground, Dock Sediments and River Terrace Deposits with very low undrained shear strengths between 2.5 to 42 kPa. The rigs to be used on site were 225 tons with applied pressures in the range of 300 to 470kPa and loadings of more than 1500kN. A series of reinforced piling mats were required to support the heavy rigs and reduce the applied pressures over the foundation soil. The design of the working platforms reinforced with geogrids was conducted in two stages, first to improve the modulus of the platform using recycled granular material, and second to provide safe platforms to support the heavy rigs.

The distributions and variations of Quaternary Thames River Terrace deposits of Greater London

A database containing c. 27 000 records of Quaternary lithostratigraphy extracted from c. 5800 boreholes drilled to a variety of depths has been compiled from information contained in logs recorded and held by the British Geological Survey (BGS) and from the Crossrail project. After ‘cleaning’ and quality assessment the raw borehole log data have been investigated for patterns in distribution, and variations in the Quaternary facies across Greater London. In particular, the analysis of Quaternary River Terrace Deposits has been focused on here and a summary of relevant published terminology and nomenclature is also included in this Technical Note, as an aid to understanding. The spatial distributions of each major Quaternary lithostratigraphic interval, as identified in the log descriptions, are also presented as point locations in map form, and in comparison with the corresponding BGS mapped outcrop patterns of the respective lithostratigraphic units. The presence of various specific clasts in the log descriptions (e.g. cobbles and chalk clasts) is also presented at stratigraphic member levels against their apparent source outcrops. For instance, cobbles recorded from the Boyne Hill Terrace intervals are concentrated in the eastern outcrops and reflect the Wealden source and former river system of the Darrent–Wid towards the Essex coast at Maldon. Similarly, the presence and distribution of shell and chalk clasts within river terrace sands and gravels reflect the geology of the underlying subcrop strata of Lower Shelly Clay and Chalk respectively. The Crossrail data also include some grain-size information from sieve analysis and some engineering in situ test values, which require careful analysis beyond the scope of this work but are potentially useful. The grain-size distributions for some of the samples from the river terrace sands and gravels show fining-up and coarsening-up sequences, and geographical grain-size trends in various stratigraphic intervals. The recorded presence of faults, fractures and fissures, as identified by the drilling contractors or logging geologists, is also extracted and mapped. Supplementary evidence, from repeated stratigraphy or improbable spatial proximity changes in subcrop depths, suggests a cause other than deposition for such changes and, on the presumption that their cause is natural, is interpreted as likely to be representative of faulting of some kind, including low-angle thrust faults. Faulting is also considered to have controlled the distribution of several interglacial silt members and is the subject of considerable research in the deeper intervals of London stratigraphy, so is only briefly dealt with here. To define the period over which tectonic structures, now known to exist within the strata of the London Basin, were active requires an analysis of Quaternary deposits that overlie them. This Technical Note provides an initial review of the data available from boreholes for such work and for any other studies requiring knowledge of these deposits. Supplementary material : Spreadsheets (and other files), and notes on the name and significance of each, are available at https://doi.org/10.6084/m9.figshare.c.6700313 Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/topic/collections/geology-of-london-and-its-implications-for-ground-engineering

Study of diagenitic processes and surface texture of the oldest river terrace deposits in Shirqat area- northern Iraq

The recent project deals with the diagenitic processes and surface textures of the oldest river terraces deposits in Shirqat area, the diagenitic processes compiled with Cementation, Compaction and Dissolution. The carbonate minerals represent the cementic materials while the point contact compaction represent the degree of compaction in this sediments because the small thickness of the overburden sediments and the secondary effects of differential dissolution. The surface texture is very developed in the large size of sediment included pebble, cobble and boulders which form very developed surface texture formed order and disorder forms as well as smooth surface texture.

Mid-Late Quaternary Fluvial Archives near the Margin of the MIS 12 Glaciation in Southern East Anglia, UK: Amalgamation of Multi-Disciplinary and Citizen-Science Data Sources

This paper presents an updated geological reconstruction of the Quaternary evolution of the River Thames at its downstream extremities, close to the North Sea coast, based on new data from multi-disciplinary and citizen-science sources. In this area, the interaction of the Thames with the MIS 12 (Anglian) glaciation is an important part of the Quaternary archive. The Anglian ice sheet, which reached parts of north and east London, was responsible for diverting the Thames southwards into its present course, although the footprint of the maximum ice sheet(s) does not reach the North Sea coast south of Hollesley, Suffolk. Further south, the coastal zone hosts pre-Anglian and early Anglian river-terrace deposits of the pre-diversion Thames system, superimposed upon which are products of later post-Anglian rivers, of both Middle and Late Pleistocene age. On the peninsula between the Stour and Blackwater–Colne estuaries, the lowest and most recent terrace of the pre-diversion Thames includes evidence directly pertaining to the glacial disruption event, for which geochronological data are reported here for the first time. The first post-diversion terrace of the Thames also reaches this peninsula, the river having essentially re-joined its original valley before crossing the alignment of the modern coastline. This terrace passes beneath Clacton-on-Sea, where it includes the type locality of the Clactonian Palaeolithic Industry. The area of interest to this paper, in NE Essex and southern Suffolk, includes a number of interglacial and Palaeolithic sites, the data from which assist in constraining the chronostratigraphy of the sequence. In some cases, there has been uncertainty as to whether these sites represent pre-Anglian environments and hominin occupations, part of the palaeo-Thames sequence, or whether they are the product of later post-Anglian streams, formed after the Thames had migrated southwards. This paper compiles evidence from a wide range of recent sources, including developer-funded archaeological appraisal and citizen-science activities, to explore and update the evidence from sites at Ipswich, Upper Dovercourt and Thorpe-le-Soken, as well as a number of localities associated with the Clacton Channel Deposits (host to the type-Clactonian), amongst others. The resulting new data are placed within the wider context of the Quaternary fluvial archives in southern Britain, with a discussion of how disparate sources of information, including the work of citizen scientists, have contributed.

Observations on the geology of the country around Chalfont St Giles, Buckinghamshire

This paper presents new field observations from the area around Chalfont St Giles and relates them to existing information from the wider Chiltern Hills region on lithostratigraphy, structural geology, geomorphological and karstic features, and landscape development. In this area the NW-SE aligned valley of the River Misbourne, an internationally rare chalk stream, and flanking interfluve plateaus form a transition zone on the chalk dipslope between the lowest elevations of outcropping chalk around Denham and the characteristic chalk valleys and clay-with-flints capped upland present from Amersham northwards. The area straddles the northernmost extent of both the Paleogene strata, represented by Lambeth Group outliers, and SW–NE aligned pre-Anglian palaeo-Thames River Terrace deposits, and contains an anomalous Lambeth Group, Quarrendon Gap, mid-slope platform. Ground investigations carried out for HS2 have helped substantiate other evidence for significant faulting across the area, with intermittent movement episodes dating from the Mid- to Late Cretaceous onwards, which have affected both the Chalk and Paleogene strata and had a major influence on shaping the valley network and wider landscape. Karstic features are widespread, including contemporary interfluve plateau level streams sinks around the Lambeth Group outliers forming active dolines, together with many concealed chalk dissolution related features. There are numerous, generally small scale, clay, chalk, sand and gravel workings most of which are long abandoned but still provide useful insights into the near surface geology.

Geochemistry and Utilization of Water from Thermal Springs of Tawang and West Kameng Districts, Arunachal Pradesh

ABSTRACT The hydrogeochemical studies provide insights about reservoir conditions of geothermal springs along with utilization of thermal waters for domestic, livestock and irrigation purposes. Most of the hot springs of Tawang and West Kameng districts of Arunachal Pradesh emanated through garnet bearing high grade gneissmigmatite-schist-quartzite sequence of the Se La Group, except for Dirang hot springs which emanate from river terrace deposits lying on the footwall of deformed quartzite-phyllite. The thermal waters are of mixed Na-Ca-HCO3-SO4-Cl type, meteoric in origin and at the same time immature in nature, moving sluggishly towards mineral-fluid equilibration zone with slow rock-water interactions. Chemical geothermometry showed wide variation in estimation of sub-surface reservoir temperature and quartz geothermometry model fits prominently to provide the most reliable reservoir temperature varying within 90±40°C. The studies recorded highest reservoir temperature of Thingbu hot spring with 133°C with very high fluoride concentration in all the hot springs except Bishum and Phudung as per BIS (2012) IS: 10500 specifications. High fluoride and sulfate concentration in thermal spring waters make it unsuitable for drinking purpose. The applicability of thermal waters for irrigation is predicted through sodium adsorption ratio (SAR) calculations which showed that waters of Dirang-2, Sorbe and Kitpi-1&2 are not suitable for irrigation purpose due to high salinity and SAR values.

Seismic Site Condition of Mainland China from Geology

AbstractWe use geology as a proxy to produce a site condition map of mainland China for seismic hazard assessment. The geology is from a 1:1,000,000-scale digital database and a 1:2,500,000-scale Quaternary map. We use the lithological descriptions and ages to assign the site condition for each geologic unit. Published site condition data are used to evaluate our mapping results. Our results agree well for the strong-motion stations in Gansu–Sichuan area, except in the mountainous area. There, the mismatches are due to our geological map scales missing narrow river terrace deposits. Our results also match well in the Shandong and Beijing Plain areas, except in thin fluvial and alluvial deposits fringing bedrock mountains. Our site-response categories match well-published average VS–depth profiles from microzonation studies of 14 major urban areas.

Large-scale urban underground hydro-thermal modelling – A case study of the Royal Borough of Kensington and Chelsea, London

The shallow subsurface of dense cities is increasingly exploited for various purposes due to the significant rise in urban populations. Past research has shown that underground activities have a significant impact on local subsurface temperatures. However, the resulting spatial variability of ground temperature elevations on a city-scale is not well understood due to the lack of sufficient information and modelling complexity at such large scales. Resilient and sustainable planning of underground developments and geothermal exploitation in the short and long-term necessitate more detailed, more reliable knowledge of subsurface thermal status. This paper investigates the impact of some common underground heat sources such as train tunnels and residential basements on subsurface temperature elevation on a large scale and highlights the influence of local geology, hydrogeology, density, and type and arrangement of the heat sources on ground thermal disturbance. To tackle the size issues and computational expenses of such a large-scale problem, a semi-3D hydro-thermal numerical approach is presented to capture the combined influence of underground built environment characteristics coupled with ground properties on ground temperature elevation within the Royals Borough of Kensington and Chelsea (RBKC), London. Numerical results show that the extent of ground thermal disturbance is mostly affected by geological and hydrogeological characteristics in permeable ground (River Terrace Deposits). Density and spatial distribution of heat sources, however, are critical parameters in ground temperature evaluation in highly impermeable ground such as London Clay Formation. The locality of temperature rise and potential ground energy within immediate impermeable ground surrounding heat sources versus significantly large extent of ground thermal disturbance in permeable ground, highlights the significant dependency of ground thermal state and geothermal potential at the studied site to the ground and underground built environment characteristics and necessitates a better understanding of shallow subsurface thermal state for a sustainable and resilient urban underground development.

Microblade remains from the Xishahe site, North China and their implications for the origin of microblade technology in Northeast Asia

Here, we discuss the earliest microblade sites in China and the development of microblade technology in greater Northeast Asia. The Xishahe site was discovered in Huliu River terrace deposits in the Nihewan Basin, North China. Chronometric dating indicates the site was first occupied ca. 29–28 ka cal BP, while the microblade remains date to about 27 ka cal BP. Xishahe has yielded some of the earliest radiocarbon dated microblade technology in China, and evidence suggests that its appearance and disappearance are positively correlated with climate change. The microblade technology identified at Xishahe is different from other, younger microblade sites in China, specifically those associated with the mature wedge-shaped core technique. Further, although the Xishahe microblade cores are well-shaped with platform preparation and could successfully produce parallel-sided flakes, the overall morphology of these cores was highly variable and lacked standardization. Obvious technological differences can be seen in microblade assemblages dating to periods before and after the Last Glacial Maximum (LGM; ca. 24–18 ka cal BP).

Tectonic and climatic controls on Quaternary fluvial processes and river terrace formation in a Mediterranean setting, the Göksu River, southern Turkey

AbstractClimate and tectonics effect the fluvial evolution of the Mediterranean Mut basin. The basin contains a river terrace staircase of 16 levels (T16–T1) ranging from 365 to 10 m above the current Göksu River in its middle and lower sections. These river terraces records tectonic uplift in the Mut basin. Optically stimulated luminescence (OSL) dating of the fluvial sediments of the youngest terrace (T16) provides a chronology for the assessment of the important impacts of climatic changes. The ages from the youngest river terrace deposits in T16 may be subdivided into two intervals: (1) 239–194.7 ka during the later part of Marine Oxygen Isotope Stage (MIS) 7, implying that the aggradation of T16 started in (the final phase of) this warm period; and (2) 187.9–171 ka during much of MIS 6. Thus, it appears that the Göksu River continued depositing sediment from an interglacial into a glacial time. The differences in climate-driven fluvial evolution between this Mediterranean fluvial system and the classical, well-studied temperate–periglacial river systems in Europe may be the result of different vegetation cover and greater thaw of more intense snowfalls.

Permeation grouting and excavation at Victoria station, London

Paid area link 6 (Pal6) underpass, a crucial tunnel connection of London Underground's Victoria station upgrade project, was engineered within notoriously difficult sub-artesian granular River Terrace Deposits (RTD) immediately below the Victorian-age District and Circle line masonry tunnel, a structure highly sensitive to ground displacements. Due to the proximity of the overlying operational railway, the consequences of ground movement were of very high risk. Historic tunnel construction in the heterogeneous RTD had limited success with permeation grouting, and face losses and instabilities occurred. For the case of Pal6, the railway tunnel overhead magnified the difficulties. Permeation grouting still remained the most feasible stabilising option, but only with significant improvements in both grouting technique and grout types. A low-risk tunnelled solution, using a bespoke and sophisticated construction approach, enabled safe continuous excavation within the severely restricted structural constraints. Successful tunnelling demanded: complete sequence recovery of the RTD for accurate soil characterisation for design of the grouting system; caution with permeation grouting; appropriate grout selection to promote permeation without claquage (uncontrolled fracturing by grout with its consequent irregular distribution), thus precisely targeting discrete zones; uniform treatment; and observational control by monitoring real-time ground movements.

Long-term controls on continental-scale bedrock river terrace deposition from integrated clast and heavy mineral assemblage analysis: An example from the lower Orange River, Namibia

Establishing relationships between the long-term landscape evolution of drainage basins and the fill of sedimentary basins benefits from analysis of bedrock river terrace deposits. These fragmented detrital archives help to constrain changes in river system character and provenance during sediment transfer from continents (source) to oceans (sink). Thick diamondiferous gravel terrace deposits along the lower Orange River, southern Namibia, provide a rare opportunity to investigate controls on the incision history of a continental-scale bedrock river. Clast assemblage and heavy mineral data from seven localities permit detailed characterisation of the lower Orange River gravel terrace deposits. Two distinct fining-upward gravel terrace deposits are recognised, primarily based on mapped stratigraphic relationships (cross-cutting relationships) and strath and terrace top elevations, and secondarily on the proportion of exotic clasts, referred to as Proto Orange River deposits and Meso Orange River deposits. The older early to middle Miocene Proto Orange River gravels are thick (up to 50m) and characterised by a dominance of Karoo Supergroup shale and sandstone clasts, whereas the younger Plio-Pleistocene Meso Orange River gravels (6–23m thick) are characterised by more banded iron formation clasts. Mapping of the downstepping terraces indicates that the Proto gravels were deposited by a higher sinuosity river, and are strongly discordant to the modern Orange River course, whereas the Meso deposits were deposited by a lower sinuosity river. The heavy minerals present in both units comprise magnetite, garnet, amphibole, epidote and ilmenite, with rare titanite and zircon grains. The concentration of amphibole-epidote in the heavy minerals fraction increases from the Proto to the Meso deposits. The decrease in incision depths, recorded by deposit thicknesses above strath terraces, and the differences in clast character (size and roundness) and type between the two units, are ascribed to a more powerful river system during Proto-Orange River time, rather than reworking of older deposits, changes in provenance or climatic variations. In addition, from Proto- to Meso-Orange River times there was an increase in the proportion of sediments supplied from local bedrock sources, including amphibole-epidote in the heavy mineral assemblages derived from the Namaqua Metamorphic Complex. This integrated study demonstrates that clast assemblages are not a proxy for the character of the matrix, and vice versa, because they are influenced by the interplay of different controls. Therefore, an integrated approach is needed to improve prediction of placer mineral deposits in river gravels, and their distribution in coeval deposits downstream.

Extracting palaeoflood data from coarse‐grained Pleistocene river terrace archives: an example from SE Spain

AbstractField‐based palaeoflood event reconstruction has the potential to contribute to the development of our understanding of long‐term landscape evolution. However, the reconstruction of past flow event histories (magnitude and frequency) over long‐term (Quaternary) timescales is fraught with difficulties. Here we make a preliminary exploration of some of the practicalities of flood reconstruction from fluvial terrace archives using commonly available sedimentological and geomorphological observations from a field perspective. We utilize Manning and palaeostage indicators to reconstruct historic events that can be used as benchmarks for a lesser used competence based approach, which is applied to coarse‐grained strath terrace deposits. We evaluate the results against gauged records for extreme and catastrophic events that affected the same region in 1973 and 2012. The findings suggest that the competence approach is most effectively applied to terrace deposits if the channel geometry is taken into account when sampling both in cross‐section and in longitudinal section and calibrated against the sedimentology for palaeo‐flow depth. Problems can arise where constrictive channel geometries allow boulder jams to develop, acting as sediment traps for the coarsest material and leading to downstream ‘boulder starvation’. Useful sites to target for palaeoflood reconstruction, therefore, would be upstream of such constrictive reaches where the coarsest transportable bedload has been effectively trapped. Sites to avoid would be downflow, where the deposited material would poorly represent palaeoflood competence. Underestimation from maximum boulder preservation and limited section exposure issues would appear to outweigh possible overestimation concerns related to fluid density and unsteady flow characteristics such as instantaneous acceleration forces. Flood data derived from river terrace deposits suggests that basal terrace geometries and coarse boulder lags common to many terrace sequences are likely the result of extreme flow events which are subsequently filled by lesser magnitude flood events, in this environmental setting. Copyright © 2016 John Wiley & Sons, Ltd.

Revision of river terrace geochronology in the Orawa-Nowy Targ Depression, south Poland: insights from OSL dating

Geochronologies of intramontane depression (basin) fluvial sedimentation enable to identify through time periods of alluviation and river erosion, and date fault movement. For these purposes the optically stimulated luminescence (OSL) dating has been applied to evaluate and to develop a geochronological framework of river terraces. We study the age of river terrace deposits of the Czarny Dunajec River and its tributaries, in the Orawa-Nowy Targ Depression situated at the contact of the Central and the Outer Carpathians; where alluvial sediment ages were derived mainly from morphostratigraphic dating. Thorough careful analysis our approach demonstrates that the OSL dates differ markedly from the previous age assignments. Alluvium of the terrace elevated 5.5–6.0m above the present-day valley floor, in terms of cementation and lithology resembling sediments described as pre-Pleistocene, was found to have been deposited ∼34ka ago (MIS 3). Sediments of the lower terraces, 3m and 3.5m high, similar in elevation and internal structure to those of the Holocene terraces, are most likely of MIS 3 and MIS 2 ages, respectively. The architecture of the terraces introduces climate as a dominant driver for terrace formation at the southern border of the depression. We conclude that the morphostratigraphic approach appears insufficient for reliable dating of river terraces, especially in areas where they might be affected by young tectonic movements. Comprehensive and credible chronostratigraphy of fluvial deposits is required, particularly in the studies of the history of the fluvial systems and seismic hazard in the Carpathians.

Drift-filled hollows in Battersea: investigation of the structure and geology along the route of the Northern Line Extension, London

Drift-filled hollows (DFHs) are a major subsurface hazard for engineering in London. They are characterized by a steeply inclined cone-shaped hollow into (sometimes through) the London Clay Formation, filled with unconsolidated fine- to coarse-grained drift and often covered by terrace gravels, making them difficult to identify at the surface. Their origin remains uncertain but most probably formed towards the end of glacial epochs by meltwater scouring, perhaps of collapsed pingos. Usually associated with tributaries to the Thames, DFHs are particularly prevalent in the Battersea area, through which the Northern Line Extension (NLE) is to be built. This study uses 283 public borehole records and site reports to build a 3D geological ground model of two known DFHs in the Battersea area to develop a more complete understanding of their origin. We show that DFHs are probably older than previously assumed, dating from the end-Anglian (Marine Isotope Stage (MIS) 12), c. 300 kyr ago, before the deposition of the River Terrace Deposits. The two DFHs modelled fall into distinct types: a small shallow DFH that is probably a purely scour feature in origin, and a larger, deeper DFH that probably formed by the scouring of a perhaps fault-controlled pingo. It is unclear whether the faults controlled pingo formation passively by acting as a conduit for water, or in a more active sense by driving ground movements. Both DFHs represent a significant hazard for the NLE and require more detailed investigations to properly constrain their extent.

The winter storms of 2013/2014 in the UK: hydrological responses and impacts

This paper outlines the hydrological aspects of the 2013/2014 winter flooding in the UK, as well as the impacts. The episode is considered in a long-term historical context and wider issues raised by the flood events are discussed briefly.

Controls on the basin-scale distribution of hydraulic conductivity of superficial deposits: a case study from the Thames Basin, UK

Controls on the basin-scale distribution of hydraulic conductivity of superficial deposits are assessed in the context of hydrological setting and basin evolution and are investigated using a case study from the Thames Basin, UK. A conceptual model of superficial deposits across the Thames Basin is used to define six lithostratigraphic classes of superficial deposits: pre-Anglian Clay-with-Flint deposits; pre-Anglian River Terrace Deposits associated with the ancestral River Thames and its tributaries; Tills formed during the Anglian glaciations; glacio-fluvial sand and gravel deposits formed during the Anglian; post-Anglian River Terrace Deposits associated with the modern-day River Thames and tributaries; post-Anglian alluvium associated with the modern-day River Thames and tributaries. Hydraulic conductivity of the superficial deposits has been estimated from grain-size distribution data, originally collected for mineral resource assessments, using the Kozeny–Carman method. Based on 6411 samples from 1416 boreholes, estimated hydraulic conductivity ranges from 0.2 to 5942 m day –1 , median and mean hydraulic conductivities are 1.67 and 26.72 m day –1 respectively, and the overall distribution of hydraulic conductivity values has a strong positive skew An apparent reduction in mean hydraulic conductivity with increasing age of the deposit is observed, particularly for the River Terrace Deposits. A reduction in maximum hydraulic conductivity at depths >10 m is also observed and the relationship between hydraulic conductivity and depth is controlled by the type of superficial deposit. At the catchment to basin scale, variation in hydraulic conductivity with depth may be explained with reference to both the deposit types and the age of the deposits. Where hydraulic conductivity is found to be intimately linked to the Quaternary evolution of the basin, through contrasts in age and deposit type, permeability variations at the basin scale may be constrained by applying a suitably refined conceptual model of the superficial deposits.

Geophysical response of slackwater and sandy terrace deposits near Savanna, Northwestern Illinois

Low-permeability clayey and silty river terrace deposits are an important component in protecting underlying aquifers from contamination by agrochemicals and other contaminants. Such deposits also record deglaciation dynamics, meltwater drainage and local climatic variations. In this study, conducted over Mississippi River terraces near Savanna, Illinois, clayey slackwater terrace deposits and sandy terrace deposits are examined using resistivity soundings, ground-penetrating radar (GPR) profiles and direct-push conductivity logs. The clayey terrace deposits are characterized by low resistivity (10–35 ohm-m) and slow GPR wave velocity (0.07 m/ns), whereas non-clayey terrace deposits exhibit much higher resistivity (169–1,762 ohm-m) and faster GPR wave velocities (0.15 m/ns). Sandy and clayey terrace deposits may thus be differentiated and mapped on the basis of their geophysical response. Models based on resistivity soundings provide reasonably accurate estimates of the thickness of clayey slackwater deposits, but fail to reveal thin sands embedded in the clayey deposits. In some cases, the full thickness of the slackwater deposits was also not revealed. GPR profiles, however, imaged these embedded shallow sands and possibly imaged deeper sands below the base of the slackwater deposits, giving more accurate estimates of thickness. GPR also accurately resolved the thickness and character of sandy terrace deposits. Direct-push conductivity logs provide both accurate estimates of the thickness of clayey slackwater terrace deposits and a means of identifying thin embedded sands. In summary, resistivity soundings image these deposits at the lowest resolution with one-dimensional models, whereas GPR provides much higher resolution showing detailed layering within the upper several meters. Direct-push conductivity logs provide the highest resolution, but are invasive and only reveal stratigraphy at one location.