OR/19/003 Discussion
| Kearsey, T, Lee, J R, and Gow, H. 2019. Buried valleys (onshore) - Version 1: scientific report and methodology. British Geological Survey Internal Report, OR/19/003. |
Buried valleys, by their nature, have little or no surface expression in the landscape. This means that they are extremely hard to map in the subsurface without the use of airborne geophysics (e.g. Sandersen & Jørgensen 2003[1]). Such data is not available nationwide across the Great Britain but its use in Denmark has revolutionised understanding of the sub-drift rockhead surface (Høyer et al., 2011[2], 2015 [3]) and in-turn the management of water resources (Viezzou et al., 2013[4]; Vilhelmsen et al., 2018[5]). The results presented here represent the best current understanding of where such features may occur onshore based principally upon borehole records. However, it should be noted there are almost certainly buried valleys that have not been identified as part of this dataset especially in areas of limited borehole coverage. The dataset should only be used to indicate where there is evidence that a buried valley may be present. Absence of evidence does not equal evidence of absence. Also, because many of the references used in this dataset were figures from reports and papers, we recommend that the data set has a nominal scale of 1:250 000. If a buried valley appears in the historical datasets (Figure 7) and the modelled thickness of buried valleys interpolated from boreholes (Figure 8) the feature is more likely to exist.
Depth information for a feature can be derived from the modelled thickness of buried valleys contour dataset, but the depth of those features greater than 40 m are combined in to one depth category which ranges from 40–162 m. These depths were combined due to relatively low numbers of boreholes that prove over 40 m of superficial deposits. Higher resolution contouring of such low-resolution data typically introduces ‘bulls eye’ artefacts into the dataset. This can be misleading to the user by implying a geometry to the buried valley that is not real.
Equally, as stated previously, the areas of s ignificant thickening derived from the boreholes dataset also incorporates basinal areas such as the Crag Basin and former glacial lake basins. These feature may obscure the presence of more subtle linear buried valleys.
The Buried Valley (onshore) dataset described here represents a baseline of BGS’ current understanding of the locations of buried valleys onshore in the Great Britain based on our currently held historical literature and borehole data. It is inevitable that some of the information may be in the light of further evidence be deemed incorrect, and require rejecting or revising. This dataset will form the basis of future research in to these features and be periodically updated to include new information becomes available.
If you have evidence of a buried valley that is not part of this dataset we would be very interested to evaluate it and consider including in future versions. Please email enquiries@bgs.ac.uk
References
- ↑ SANDERSEN, P B, and JØRGENSEN, F. 2003. Buried Quaternary valleys in western Denmark—occurrence and inferred implications for groundwater resources and vulnerability. Journal of Applied Geophysics, Vol. 53, 229–248.
- ↑ HØYER, A-S, LYKKE-ANDERSEN, H, JØRGENSEN, F, and AUKEN, E. 2011. Combined interpretation of SkyTEM and high-resolution seismic data. Physics and Chemistry of the Earth, Parts A/B/C, Vol. 36, 1386–1397.
- ↑ HØYER, A S, JØRGENSEN, F, SANDERSEN, P B E, VIEZZOLI, A, and MØLLER, I. 2015. 3D geological modelling of a complex buried-valley network delineated from borehole and AEM data. Journal of Applied Geophysics, Vol. 122, 94–102.
- ↑ VIEZZOLI, A, JØRGENSEN, F, and SØRENSEN, C. 2013. Flawed Processing of Airborne EM Data Affecting Hydrogeological Interpretation. Groundwater, Vol. 51, 191–202.
- ↑ VILHELMSEN, T, MARKER, P, FOGED, N, WERNBERG, T, AUKEN, E, CHRISTIANSEN, A V, BAUER-GOTTWEIN, P, CHRISTENSEN, S, and HØYER, A-S. 2018. A Regional Scale Hydrostratigraphy Generated from Geophysical Data of Varying Age, Type, and Quality. Water Resources Management, in press.