David R. James

Bio: David R. James is an academic researcher from Cardiff University. The author has contributed to research in topics: Urban heat island & Groundwater. The author has an hindex of 4, co-authored 7 publications receiving 95 citations.

Mapping shallow urban groundwater temperatures, a case study from Cardiff, UK

Abstract: Low-enthalpy ground source heating systems can help to reduce our dependence on fossil fuels, in turn reducing greenhouse gas emissions and increasing energy security. To de-risk and support the sustainable development, regulation and management of ground source heating systems in urban areas, detailed baseline mapping of groundwater temperatures is required. Groundwater temperatures were measured in 168 monitoring boreholes primarily within a Quaternary sand and gravel aquifer in the city of Cardiff, UK. The data have been used to create the first city-wide map of shallow groundwater temperatures in the UK. This map can be used both to support development of ground source heating and to act as a detailed baseline from which to measure change. Shallow groundwater temperatures under the city were found to be 2°C warmer than the UK average groundwater temperature and this additional heat is attributed to the urban heat island. The zone of seasonal fluctuation varies from 7.1 and 15.5 m below ground level (mbgl) within the shallow Quaternary aquifer, averaging 9.5 mbgl. Deeper groundwater temperature profiles incorporating both the Quaternary and bedrock aquifers suggest that a ‘zone of anthropogenic influence’ exists down to about 70 mbgl.

Establishing an urban geo-observatory to support sustainable development of shallow subsurface heat recovery and storage

Abstract: Low-enthalpy ground source heating and cooling is recognized as one strategy that can contribute towards reducing reliance on traditional, increasingly insecure, CO2-intense thermal power generation, as well as helping to address fuel poverty. Development of this technology is applicable in urban areas where high housing density often coincides with the presence of shallow aquifers. In urban areas groundwater temperatures can be elevated owing to the subsurface urban heat island effect. Uptake and development of this technology is often limited by initial investment costs; however, baseline temperature monitoring and characterization of urban aquifers, conducted in partnership with local authorities, can provide a greater degree of certainty around resource and sustainability that can facilitate better planning, regulation and management of subsurface heat. We present a novel high-density, city-scale groundwater temperature observatory and introduce a 3D geological model aimed at addressing the needs of developers, planners, regulators and policy makers. The Cardiff Geo-Observatory measures temperature in a Quaternary aged sand and gravel aquifer in 61 boreholes and at a pilot shallow open-loop ground source heating system. We show that repurposing existing infrastructure can provide a cost-effective method of developing monitoring networks, and make recommendations on establishing similar geo-observatories. Thematic collection: This article is part of the Measurement and monitoring collection available at: https://www.lyellcollection.org/cc/measurement-and-monitoring

Shallow groundwater temperatures and the urban heat island effect: the first U.K. city-wide geothermal map to support development of ground source heating systems strategy

Abstract: U.K. Government aims to reduce greenhouse gas emissions by 80% by 2050 (Climate Change Act, 2008). Ground source heating systems could contribute to the U.K.’s energy future but uptake has been slow due to a lack of case studies. The aim of this work was to produce the 1st U.K. city-wide heat map to support the development of ground source heating. We also sought to describe groundwater temperature variation with lithology & estimate the available thermal energy beneath the city.

Subsurface sediment remobilization and fluid flow in sedimentary basins: an overview

Abstract: Subsurface sediment remobilization and fluid flow processes and their products are increasingly being recognized as significant dynamic components of sedimentary basins. The geological structures formed by these processes have traditionally been grouped into mudvolcano systems, fluid flow pipes and sandstone intrusion complexes. But the boundaries between these groups are not always distinct because there can be similarities in their geometries and the causal geological processes. For instance, the process model for both mud and sand remobilization and injection involves a source of fluid that can be separate from the source of sediment, and diapirism is now largely discarded as a deformation mechanism for both lithologies. Both mud and sand form dykes and sills in the subsurface and extrusive edifices when intersecting the sediment surface, although the relative proportions of intrusive and extrusive components are very different, with mud volcano systems being largely extrusive and sand injectite systems being mainly intrusive. Focused fluid flow pipes may transfer fluids over hundreds of metres of vertical section for millions of years and may develop into mud volcano feeder systems under conditions of sufficiently voluminous and rapid fluid ascent associated with deeper focus points and overpressured aquifers. Both mud and sand remobilization is facilitated by overpressure and generally will be activated by an external trigger such as an earthquake, although some mud volcano systems may be driven by the recharge dynamics of their fluid source. Future research should aim to provide spatio-temporal \\\\\\\'injectite\\\\\\\' stratigraphies to help constrain sediment remobilization processes in their basinal context and identify and study outcrop analogues of mud volcano feeders and pipes, which are virtually unknown at present. Further data-driven research would be significantly boosted by numerical and analogue process modelling to constrain the mechanics of deep subsurface sediment remobilization as these processes can not be readily observed, unlike many conventional sediment transport phenomena.

Coupled discrete element modeling of fluid injection into dense granular media

Abstract: [1] The coupled displacement process of fluid injection into a dense granular medium is investigated numerically using a discrete element method (DEM) code PFC2D® coupled with a pore network fluid flow scheme. How a dense granular medium behaves in response to fluid injection is a subject of fundamental and applied research interests to better understand subsurface processes such as fluid or gas migration and formation of intrusive features as well as engineering applications such as hydraulic fracturing and geological storage in unconsolidated formations. The numerical analysis is performed with DEM executing the mechanical calculation and the network model solving the Hagen-Poiseuille equation between the pore spaces enclosed by chains of particles and contacts. Hydromechanical coupling is realized by data exchanging at predetermined time steps. The numerical results show that increase in the injection rate and the invading fluid viscosity and decrease in the modulus and permeability of the medium result in fluid flow behaviors displaying a transition from infiltration-governed to infiltration-limited and the granular medium responses evolving from that of a rigid porous medium to localized failure leading to the development of preferential paths. The transition in the fluid flow and granular medium behaviors is governed by the ratio between the characteristic times associated with fluid injection and hydromechanical coupling. The peak pressures at large injection rates when fluid leakoff is limited compare well with those from the injection experiments in triaxial cells in the literature. The numerical analysis also reveals intriguing tip kinematics field for the growth of a fluid channel, which may shed light on the occurrence of the apical inverted-conical features in sandstone and magma intrusion in unconsolidated formations.