OR/14/013 Modelled volume, purpose and scale

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Monaghan A A, Arkley S L B, Whitbread K, McCormac M. 2014. Clyde superficial deposits and bedrock models released to the ASK Network 2014: a guide for users Version 3 . British Geological Survey Internal Report, OR/14/013.

Acknowledgements

A large number of individuals from the Clyde Basin Urban Superproject (CUSP) have contributed to this work. We would particularly like to thank the following: Tony Irving, Bill McLean and Sandy Henderson for data entry and compilation, and the modellers additional to the report authors — Jo Merritt, Sue Loughlin, Andrew Finlayson, Tim Kearsey, Charlotte Vye-Brown, Ricky Terrington and Gaud Pouliquen. Dave Lawrence played a key role in inserting water into the revised models. Lauren Noakes, Keith Henderson and Lesley Oliver assisted in model quality control and model exports.

Summary

This report provides an overview of all the Clyde superficial deposits and bedrock models released to the ASK (Accessing Subsurface Knowledge) knowledge exchange network in January 2013, June 2013 and March 2014. The geological models are an interpretation of digital datasets held by the British Geological Survey.

A summary of the construction and limitations of the models and a brief description of the modelled units is given. The report will be updated and revised as more models become available for release to the ASK network.

More details on the models can be found in the reports Merritt et al. (2009)[1], Monaghan (2012a)[2], Monaghan et al. (2012)[3], McCormac (2013)[4]. This report supersedes Arkley et al. (2013)[5] and Monaghan et al. (2013)[6].

Superficial deposits

Figure 1 Superficial deposits model areas.

The Superficial Deposits Models of the Glasgow area were constructed in tiled areas (Figure 1) for reasons of computing power and software capability. In January 2013, the Central Glasgow tile was released to the ASK (Accessing Subsurface Knowledge) knowledge exchange network which has the corner coordinates SW 255000, 660000 to NE 265000, 670000. In June 2013

superficial deposits models with corner coordinates SW 245000, 655000 to NE 265000, 675000 comprising the South Glasgow, Paisley, Clydebank, and North Glasgow models were released. Note that due to data availability, the Clydebank and South Glasgow models do not cover the full sheet extents as implied in Figure 1. The Coatbridge and South-east Glasgow models with corner coordinates SW 265000, 665000 to NE 275000, 670000 are now (March 2014) being released. The model Z values or depths are all given in metres relative to Ordnance Datum (OD) and range from approximately +230 to -80 m.

The Superficial Deposits Models are most suitable for use at scales between 1:10 000 to 1:50 000 but are also useful for providing guidance at other scales.

The purpose of the Superficial Deposits Models is to give a broad indication of the likely subsurface sequence from Devensian glacial till to artificial (man-made) deposits across Glasgow for use during the desk study stage, in for example the assessment of potential infrastructure alignments and locations, and relatively broad scales of planning. However, the model is also well suited to act as a guide for studies at more detailed scales, and especially as a basis for planning and improving the economic efficiency of, site investigations. However, users are advised against basing interpretations on extreme exaggeration of the vertical or horizontal scales of the models.

The Superficial Deposits Models were improved in 2012–14 to be fully consistent with surrounding models and to include some new cross-sections in the south-west part of the model, compared to earlier versions supplied by the British Geological Survey to Clyde Gateway Developments Ltd, Glasgow City Council, South Lanarkshire Council and Scottish Enterprise. Versions supplied to the ASK Network in March 2014 are version 3 of the Central Glasgow model and version 2 of the surrounding tiles.

Bedrock

Figure 2 Image showing the extent of the Central Glasgow Bedrock Model and the extent of the lower resolution Clyde Catchment scale bedrock model (blue), provided to the ASK Network as a clipped 10 km buffer around the Central Glasgow bedrock model.

Bedrock modelling has been undertaken at a variety of scales by the British Geological Survey in the Clyde Catchment. The model scale is dependent on the data available and used, the number of coal seams, stratigraphic surfaces and faults included in the model.

The Central Glasgow Bedrock Model provided to the ASK network is the same as the Version 2 model supplied to Clyde Gateway Developments Ltd, Glasgow City Council, South Lanarkshire Council and Scottish Enterprise in early 2012. It has the corner coordinates SW 255000, 660000 to NE 265000, 670000. A lower resolution Clyde Catchment scale bedrock model is also now provided with the corner coordinates SW 250000, 655000 to NE 270000, 680000. The model Z values or depths are all given in metres relative to Ordnance Datum (OD) with the modelled surfaces extending to c.-1100 m depth, with the largest faults projecting down to c. -2.5 km

The Central Glasgow Bedrock Model is most suitable for use at scales from 1:10 000 to 1:50 000 but is also useful for providing guidance at other scales. The Clyde Catchment scale model provided for the buffer zone is most suitable for use at scales between 1:100 000 to 1:250 000.

Note that because the Clyde Catchment bedrock model was undertaken at a different scale from the Central Glasgow bedrock model, contains fewer faults and larger mesh/grid spacing, the two models are not edge matched. The Clyde Catchment bedrock model has simply been cut to the 10 km buffer zone (Figure 2) provided to the ASK Network, that is, the Z value of the modelled horizons is not necessarily the same at any given point along the model boundary and the fault positions do match exactly in 3D space. The maximum difference is of the order of 20 m on the Glasgow Ell (GE) surface and 90 m on the base Upper Limestone Formation (bULGS) surface. These differences give an indication of the model uncertainty at depth where the modelled surfaces are poorly constrained by borehole or mine plan data.

The purpose of the bedrock models was to specify in 3D the geometry and faulting of some key, mined coal seams for use in outline planning and development, and key stratigraphic surfaces for regional geological correlation.

Datasets provided to users

The Superficial Deposits Models were created in the GSI3D modelling software and have been converted to ASCII grids and ESRI (ArcGIS) raster grids for supply to users, and encrypted within Lithoframe Viewer software for 3D visualisation, synthetic sections and boreholes.

For the ASCII grids, these are provided in folders by block model area and with a base (e.g. witi_dmtn_b.asc), top (e.g. witi_dmtn_t.asc) and thickness (e.g. witi_dmtn_th.asc). Lenses only have a top.

The stratigraphic and rock type codes used in the exported model grids are described in section 2. In addition the qualifiers _t, _b and _th are used to indicate the unit top, base and thickness respectively.

For the ESRI grids, the base (e.g. witi_dmtn_b) and top (e.g. witi_dmtn_t) have been merged across the whole of the 5 block model areas. Outlines of the modelled unit extent (‘envelope’) are supplied as ESRI shapefiles across the 5 block areas (and beyond).

The resolution of the superficial deposit ASCII and ESRI grids is 25 m.

The Lithoframe Viewer software and an accompanying manual can be downloaded from the BGS website at http://www.bgs.ac.uk/services/3Dgeology/lithoframeSamples.html. Note that in some versions of Windows it is necessary to paste in the .GSIPRe file location and name to the ‘Load model’ screen, loading of the models and refreshing of the 3D window may take a few minutes, and that creating a horizontal slice in the Lithoframe Viewer takes a considerable time (20 minutes).

The Central Glasgow and Clyde Catchment scale bedrock models were created in the GOCAD® modelling software and have been converted to ESRI grids for supply to users. The surface grids and a combined fault grid were exported from the modelled GOCAD® TIN’s using a grid spacing of 25 m for the Central Glasgow bedrock model and 50 m for the Clyde Catchment scale bedrock model. The stratigraphic codes used for naming the modelled surfaces are described in section 2.

Examples of uncertainty layers are also provided as images or ASC files; these are described further in section 8 of this report. Further uncertainty layers will be provided to the ASK Network on delivery of all the superficial deposits models.

References

  1. MERRITT, J E, MONAGHAN, A A, LOUGHLIN, S C, MANSOUR, M, Ó DOCHARTAIGH, B É and HUGHES, A G. 2009. Clyde Gateway Pilot 3D Geological and Groundwater Model. British Geological Survey, Commissioned Report, CR/09/005.
  2. MONAGHAN A A. 2012a. Model metadata report for the Clyde Gateway v2 bedrock model. British Geological Survey Internal Report, IR/12/006.39pp.
  3. MONAGHAN A A and WHITBREAD K. 2012. Shieldhall High Resolution 3D Model. British Geological Survey Commercial in Confidence Report, CR/12/076. 35pp
  4. MCCORMAC, M. 2013. Clyde Catchment GOCAD® bedrock regional model, 2013. British Geological Survey Internal Report, IR/13/014. 11pp
  5. ARKLEY S, WHITBREAD K and MONAGHAN A. 2013. Clyde superficial deposits and bedrock models released to the ASK Network 2013: a guide for users. British Geological Survey Open Report, OR/13/002. 35pp.
  6. MONAGHAN A A, ARKLEY S L B, WHITBREAD K and MCCORMAC M. 2013. Clyde superficial deposits and bedrock models released to the ASK Network 2013: a guide for users Version 2. British Geological Survey Open Report, OR/13/025.35pp.