Stephanie Bricker

Anomalous buried hollows in London: development of a hazard susceptibility map

Engineering works carried out in central London over many decades have revealed a number of buried hollows that exhibit curious characteristics. Some extend deep into the bedrock geology and are in-filled with disturbed superficial deposits and reworked bedrock. Others are contained within the superficial deposits. They can be up to 500 m wide and more than 60 m in depth. As the infill material often has different behavioural characteristics from the surrounding deposits failure to identify them during an initial site investigation can prove costly. This paper considers their common characteristics and describes the method used to develop a buried hollow hazard susceptibility map. This map provides planners with a broader awareness of the potential location of difficult ground conditions associated with them, thereby reducing the potential for unforeseen ground conditions through effective site investigation design. The paper continues with a discussion of some of the likely processes associated with their formation, which are attributed to cryogenic processes, and concludes with potential future research directions.

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.

Superficial Hollows and Rockhead Anomalies in the London Basin, UK: Origins, Distribution and Risk Implications for Subsurface Infrastructure and Water Resources

Recent findings in London show that the subsurface is much more complex than expected, with a number of apparently anomalous features that present a direct hazard to infrastructure development and a risk to ground water management. Of these features, one of the least understood are the large superficial hollows which occur in the rockhead—in much of the London Basin, this is the top of the London Clay Formation—and which are infilled by a range of Quaternary deposits, principally alluvial sands and gravels deposited by the River Thames and its tributaries. The hollows range in size and shape. Several are a few hundred metres across and can be up to 40–50 m deep, though determining their exact form is problematic. The soil and sediment infill of the hollows differs substantially from the surrounding ground in terms of strength and drainage, as well as some differences in chemistry. This presents a real hazard to infrastructure as there is a potential for vertical and horizontal movement, flooding, as well as increasing the risk of contamination of the deeper aquifer. In the paper, the locations and characteristics of known hollows and deformed strata are reviewed and evidence for how they formed is reassessed, systematically considering different hypotheses (scour, ground ice, karst subsidence, seismo-tectonic). From this we consider the implications for continued development of subsurface infrastructure development, and for water resources.

The Development of Linked Databases and Environmental Modelling Systems for Decision-Making in London

A basic requirement for a city’s growth is the availability of land, raw material and water. For continued and sustainable development of today’s cities we must be able to meet these basic requirements whilst being mindful of the environment and its relationship with anthropogenic activity. The heterogeneous and complex nature of urban systems where there are obvious environmental and anthropogenic inter-dependencies necessitates a more holistic approach to decision-making. New developments such as linked databases of environmental data and integrated environmental modelling systems provide new ways of organising cross-disciplinary information and a means to apply this to explain, explore and predict the urban systems response to environmental change. In this paper we show how, accessibility to linked databases, detailed understanding of the geology and integrated environmental modelling solutions has the potential to provide decision-makers and policy developers with the science based information needed to understand and address these challenges.

Can sustainable development be achieved if geology is ignored

“Sustainable development” implies that a stable relationship between human activities and the natural world is possible such that the prospects of future generations do not diminish. Can this really be achieved in our urban centres where social and economic issues are often the driving force behind development? Geoscience information has traditionally been under-utilised in planning and development, because all too often its relevance and significance is misunderstood or underappreciated. However, this is starting to change. Using case studies from London and the Thames Gateway Development Zone, this paper discusses how technological developments, such as improvements in GIS technologies and 3D modelling software, are driving this turnaround. The paper also considers the impact of organisations not sharing ground investigation geodata and know-ledge about anomalous ground conditions across London, the huge benefits that data sharing can offer and how lessons learned in this study can be applied to other urban centres. The paper will show that within the environmental ecosystem, if one component part is misunderstood, then developing sustainably without compromising future needs will be difficult, if not impossible, to achieve. In London, difficult ground conditions cost developers time and money through project overruns and expensive engineering solutions. A more sustainable solution is in improving our understanding of the relationship between the geology (lithology) and its properties (physical, chemical or hydrological characteristics). We will show that for the urban underground to be fully utilised throughout Europe, the lack of development policies for the subsurface needs to be addressed. For a subsurface development policy to be written, stakeholders will need to regard the urban underground as environmentally sensitive, just as it does for the surface.