OR/17/003 Data

Terrington, R, Thorpe, S and Jirner, E. 2017. Enköping Esker pilot study - workflow for data integration and publishing of 3D geological outputs. British Geological Survey Internal Report, OR/17/003.

Detailed description about data provided by SGU to BGS for preparation into 3D modelling software.

Projection system

SWEREF99_TM
WKID: 3006 Authority: EPSG
Projection: Transverse_Mercator
False_Easting: 500000.0
False_Northing: 0.0
Central_Meridian: 15.0
Scale_Factor: 0.9996
Latitude_Of_Origin: 0.0
Linear Unit: Meter (1.0)

Geographic Coordinate System: G
Angular Unit: Degree (0.0174532925199433)
Prime Meridian: Greenwich (0.0)
Datum: D_SWEREF99

Spheroid: GRS_1980

Semimajor Axis: 6378137.0

Semiminor Axis: 6356752.314140356

Inverse Flattening: 298.257222101

Area of interest

Area of interest: Enköping.
Enkoping is situated near Lake Mälaren, about 78 km west of Stockholm and has approximately 22 000 inhabitants. It is also close to other large Swedish cities such as Uppsala and Västerås.

The total area that was under consideration 126² km. The total area of the calculated model was 46² km which was buffered around the central area in which contained the esker itself (Figure 1).

Figure 1    Enköping Location and Model Boundary (ESRI Streets Base Map).

The depth to which the model was to be modelled was to the base of the superficial deposits (i.e. geological rockhead), with an undifferentiated bedrock unit forming the base of the model. The maximum thickness of superficial deposits encountered beneath the study area was 46 m according to the national superficial deposits thickness model (Superficial deposits thickness).

Geological map linework

The geological map provided is 1:50 000 scale and shows the main lithological units with no stratigraphic sub-division. The surficial geology of the area is dominated by clay and till with the esker itself composed of a mixture of sand, boulders and clay (Figure 2). The esker feature (Isälvssediment) is highlighted by the black outline in the figure below, showing the surface distribution of the esker.

Figure 2    Quaternary Geology Map.

Figure 3    Borehole distribution map.

Boreholes datasets

Three borehole datasets have been provided in Excel and Shapefile format. These boreholes were missing a start height (collar height) value. The surface elevation value from the DTM was used as the ground level value. The boreholes are classified based upon their bulk lithological properties and possess a varying degree of detail. A summary of the borehole datasets provided are below including a map showing the distribution of the borehole datasets (Figure 4).

Figure 4    Example Borehole Attribute Table — SGU Boreholes.

SGU boreholes and boreholes (investigation boreholes)

Although these were provided as two datasets, these should be considered as one dataset as they are essentially showing the same information and will be merged into the same database by SGU in the future. 16 SGU boreholes were available to the study although these were principally restricted to the northern part of the Esker, with 3 boreholes south of the mapped esker feature. These were provided by SGU from their Hydrogeological Database (HPAR) which contain both SGU and consultant reports. Boreholes range from a few metres to approximately 33 m in depth. The boreholes had a limited lithological description recorded (Figure 5).

Figure 5    Borehole Attribute Table — Boreholes.

The ‘Boreholes’ contained a total of 38 boreholes with approximately 19 boreholes within the Esker boundary as shown on the geological map. This was provided by SGU from their JSTR database, which is a stratigraphy database containing various datasets including geotechnical reports and sections from pits. These range in depth from a few metres to approx. 36 m. Many of the boreholes were clustered in the central part of the Esker area. This borehole dataset tended to be limited in the description of the lithology, usually stating the dominant 2 lithologies with little in the way of description apart from stating the main lithological units, e.g. Lera-Silt = Clay Silt or Sand-Block = Sand-Boulders (Figure 6).

Figure 6    Borehole Attribute Table — Wells.

Wells

The ‘Wells’ (BARK) archive dataset contained a total of 428 boreholes with 22 occurring within the esker boundary according to the geological map. The Wells Archive contains information on the technical design, depth, yield, groundwater level, geographical location, soil depth etc. of around 500 000 wells and boreholes. It is based on the reports which, since 1976, all well drillers have been required by law to submit to SGU. These were evenly and widely distributed across the esker area. Boreholes extend to over 200 m below ground level in places. Two or three lithological units have been described, with little or no geotechnical description coded (Figure 7).

Figure 7    Digital Elevation Model.

Digital terrain model

A 2 m LiDAR dataset was provided by SGU for the area of interest and the wider area. For the geological modelling this was sub-sampled to 5 m horizontal resolution to ensure software performance was maintained in both the SubsurfaceViewer and GSI3D software. (Figure 8). In Groundhog software, the horizontal resolution of 2 m was retained for all snapping and checking after a draft of the model was produced in the SubsurfaceViewer.

Figure 8    All Georadar and seismic profile locations.

Geophysics

Two sets of geophysical data have been provided which were mainly restricted to the northern half of the model area with two Georadar (Ground Penetrating Radar) lines south of the main Esker feature (Figure 9).

Figure 9    Georadar image with groundwater level interpreted.

Georadar (GPR)

There were 18 TIFF images of the georadar sections that have been depth converted, some of which have been partially interpreted based on the colour scheme below. Examples of these can be seen in the following figures (10, 11 and 12):

Red = Bedrock
Yellow = Clay
Blue = Groundwater

Of the 18 Georadar images, only the following have had some form of interpretation. These are:

R1-01.tif (Only groundwater shown)
r2-01.tif — some clay
R3-01.tif — some clay
r5-01.tif — Only bedrock. No correlation added
r6-01.tif — some clay
r8-01.tif — Only bedrock. No correlation added

Figure 10    Georadar image with clay interpreted.

Figure 11    Georadar image with clay and top of bedrock interpreted.

Figure 12    Locations of Interpreted Georadar (GPR) with major and minor roads.

Figure 13 shows the location of the seismic and georadar profiles.

Figure 13    Example seismic section figure.

Seismic profiles

Five depth converted seismic profiles exist in and around the Enköping Esker. These have been interpreted and can be used directly for cross-section interpretation (Figure 14):

S1-01 — Clay overlying Sand and gravel
S2-01 — Silt — Overlying silt and sand
S3-01 — Didn’t match DTM?
S4-01 — Sand overlying Silt? Correlated as Sand and gravel
S4-02 — Sand and gravel

Figure 14    Topographic Map — Enköping.

The location of these seismic lines are restricted to the northern part of the Esker (Figure 13).

Imagery/topological data

Topology imagery provided by SGU (Figure 15).

Figure 15    SGU Superficial Deposits Thickness Model.

Superficial deposits thickness

The superficial deposits thickness grid was supplied from the SGU national model. This was sampled at 10 m cell size and in the area of interest is up to 46 m thick (Figure 16). Rockhead has also been calculated by subtracting the superficial deposits thickness from the DTM which can aid the interpretation where there is little borehole geophysical constraint in cross-section.

Figure 16    Cross-Section Locations.

GVS/legend

A pre-existing generalised vertical section (GVS) and model legend (.gleg) from the Uppsala geological model was used for Enköping Esker model, but later modified in discussion with SGU (Table 1).

Table 1    GVS for Enköping Geological Model

Name	id	Stratigraphy	UNIT_TYPE	English Translation
Vatten	10	Vatten	Vatten	Water Body
Ospecifierat	20	Ospecifierat	Ospecifierat	Unspecified/Artificial Ground
Organiskt sediment	30	Organiskt sediment	Organiskt sediment	Organic matter
Svallsediment	40	Svallsediment	Svallsediment	Outwash Material
Lera	50	Lera	Lera	Clay
Isälvssediment	60	Isälvssediment	Isälvssediment	Primary glaciofluvial
Morän	70	Morän	Morän	Till
Berggrund	80	Berggrund	Berggrund	Bedrock

Table 2    Legend for Enköping Geological Model (model units only)

Name	Description	R	G	B	Transparency	Texture
Vatten	Vatten	255	255	255	255	TEXTURES\black.jpg
Ospecifierat	Ospecifierat	0	0	0	255	TEXTURES\black.jpg
Organiskt sediment	Organiskt sediment	217	191	158	255	TEXTURES\black.jpg
Svallsediment	Svallsediment	243	149	63	255	TEXTURES\black.jpg
Lera	Lera	255	255	0	255	TEXTURES\black.jpg
Isälvssediment	Isälvssediment	128	255	38	255	TEXTURES\black.jpg
Morän	Morän	217	247	255	255	TEXTURES\black.jpg
Berggrund	Berggrund	230	230	230	255	TEXTURES\black.jpg

Additional model data

A study for groundwater was conducted by GEOSIGMA, entitled ‘Enköpingsåsen Hydrogeoutredning’ and published in November 2012, which covered a large proportion of the esker in Enköping. There are several boreholes, maps, cross-sections and surfaces which might be useful to include within the model. The surfaces needed further formatting and refinement before they can be incorporated directly in this model. Further investigation is also required to convert these into a suitable format. However, boreholes from this additional dataset proved not to be adequate in detail or depth to improve the geometries of the units constructed.