All borehole data and synthetic data were sampled to the AltaLIS 15 m provincial digital elevation model (DEM; resampled to 200 m grid cell resolution) to provide a borehole top elevation (m asl) from which to correlate strata between boreholes and to create the basal coarse-grained sediment isopach grid. This process was necessary as the elevation of AWWID water wells, in many cases, was not available/recorded or verified, and if reported, was estimated from a topographic map, field investigation or handheld Global Positional System (GPS) device. GPS devices have accuracies reported by the AWWID of ~1–30 m, but are of varying device quality and cannot be assessed for accuracy between devices. Elevation values of moderate-and high-quality data were also checked with the DEM to verify elevation accuracy and modified to match the DEM, if necessary.
Original elevation information for subsurface information that was not sourced from the AWWID (i.e., AGS boreholes and field data, and geophysical logs), was deemed high quality; comparisons were made between the elevation information and the DEM to ensure the correctness of the original elevation information. If the original elevation data from a borehole or field site was approximately the same as the DEM the original elevation information was used. Where original elevation information deviated from the DEM, the DEM value was used at that location.
The vertical accuracy of the 12 m DEM is stated as 5 m @ 90% where derived from 1:60 000 aerial photographs using photogrammetric methods.
Modelling software used to create grid: ESRI® ArcMap™ 10.6.1 (grid interpolation) and Viewlog™ (deterministic alterations)
Number of data points available: 30227
Data sources: A variety of low- to high-quality multisource data were used including borehole and field data, geospatial datasets in GIS format, and published gridded information. Borehole data consists of lithologs submitted by water well contractors and compiled in the Alberta Water Well Information Database (AWWID), downhole geophysical logs collected from water wells, AGS drillholes and field data, as well as industry information.
Cross-sections of these data sources were plotted in Viewlog™ to generate stratigraphic picks of basal coarse-grained sediment (BCGS).
Cell Size: 200 m
Grid Interpolation Information:
An isopach of basal coarse-grained sediment (BCGS) thickness was interpolated using the Geostatistical Analyst extension of ESRI® ArcMap™ 10.6.1. The isopach was edited by a Boolean grid to assign 0 m thickness values in areas where 1) the thickness was less than 2 m, or 2) the contiguous BCGS body was less than 2 square kilometres (200 ha) in area. The edited isopach was added to the bedrock topography and edited where it intersected the surface DEM to produce the BCGS structure top surface.
The following Method Report and Prediction Errors provide information about the parameters used to create the isopach grid, and any errors associated with the gridding process.
Method Report:
Method: Kriging
Type: Ordinary
Output type: Prediction
Variogram: Semivariogram
Number of lags: 12
Lag size: 222.35
Nugget: 23.18
Measurement error percentage: 100
Model type: Gaussian
Range: 1778.79
Anisotropy: No
Partial sill: 18.54
Prediction errors:
Mean: -0.003
Root mean square error: 5.42
Mean standardized: 0.000
Root mean square error, standardized: 0.98
Average standard error: 5.58
Error exclusion: 0
Number of points excluded: 0
Percent error exclusion: 0
Deterministic Grid Alteration Information:
Basal coarse-grained sediment (BCGS) isopach gridded data was modified in ESRI® ArcMap™ 10.6.1 by the following grid math procedures and exported as an ASCII grid:
1) Developing a Boolean grid filter based on the unedited BCGS isopach grid to determine where the BCGS unit exists. The value ‘1’ denotes BCGS is present and has a modelled thickness greater than 2 m and a contiguous area greater than 200 ha; the value ‘0’ indicates the calculated isopach grid is equal to 0 m, and BCGS is absent.
2) Multiplying the calculated isopach grid of BCGS by the Boolean grid and adding the resultant grid to the underlying bedrock topography to achieve an elevation (m asl) surface for the top of BCGS.
3) Constraining the top of the BCGS elevation grid by the bounding unconformable surfaces of the surface topography (i.e., the DEM; resampled to a 200 m cell size).