This dataset is part of the 3D hydrostratigraphic model of the Calgary-Lethbridge Corridor (CLC), southwestern Alberta. It represents the structure top of hydrostratigraphic unit (HSU) S2, which contains coarse-grained glaciofluvial and fluvial sediments that are distributed throughout the modern drainage system. HSU S2 overlies HSU C in the Neogene-Quaternary succession of the CLC and is the top boundary of the model domain.
This dataset supplements Alberta Geological Survey (AGS) Report 91, which includes a full description of steps taken to produce the structure grid.
Numerous water wells from the AWWID were used in the study to broadly define hydrostratigraphic units in the Neogene-Quaternary succession. The AWWID has abundant, relatively low quality data records, which include location inaccuracies resulting in up to 10 wells with duplicate locations. In cases of collocated data, where three or more wells with the same location information were encountered in the database, the deepest and shallowest well logs were selected to include wells that were completed in bedrock and to also characterize near surface sediments.The remaining duplicate wells were omitted.
The original input data were classified using unpublished hydrostratigraphic assignments to create a laterally extensive and mappable geobody. Classification of lithological data into hydrostratigraphic units may incorporate assumptions and human error when simplifying complex geological data, as unit geometry, extent, and description are a product of the author’s conceptual understanding. The HSU S2 grid is for use in regional-scale groundwater studies, as these mappable hydrostratigraphic units may be more complex or absent at the scale of a local investigation.
This grid represents all areas within the geographic boundary of the HSU S2.
All borehole data from the AWWID were sampled to the 25 m Provincial Digital Elevation Model (DEM) to provide a borehole top elevation (m asl). This process was necessary because the borehole top 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. Elevation values of moderate- and high-quality data from AGS boreholes and field sites, geophysical logs, and previously published geological and hydrogeological maps were also checked with the DEM to verify elevation accuracy and modified to match the DEM, if necessary.
The vertical accuracy of the 25 m DEM is stated as 5 m @ 90% in the CLC derived from 1:60 000 aerial photographs using photogrammetric methods.
Methodology to create this grid dataset is fully documented in AGS Report 91.
Modelling Program used to create grid: ArcMap (grid interpolation) and RockWorks16 (deterministic alterations)
Number of data points available: 1241
Data type: A variety of low- to high-quality borehole data were used including lithologs submitted by water well contractors and compiled by the AWWID, downhole geophysical logs collected from water wells, and AGS borehole logs and field data.
Cell Size: 400 m
The Geostatistical Analyst ArcMap extension was used to interpolate the elevation value for the base of HSU S2. The base elevation of HSU S2 is equal to the top elevation of HSU C. The Method Report and Prediction Errors for interpolation of the base of HSU S2 and the top of HSU C are fully documented in DIG 2016-0034.
The extent of the top of HSU S2 was determined by evaluating the HSU S2 thickness grid where thickness values were >0 m. The HSU thickness grid was generated by subtracting the top of HSU C from the DEM, which was considered the top of the model domain.
Deterministic Grid Alteration Information:
All HSU gridded data in the CLC model (HSU S2, C, and S1) as well as the CLC bedrock topography were exported as ESRI ascii grids from ArcMap and imported into RockWorks16 for integration into the full hydrostratigraphic model.
Modelling constraints applied: The grid of the top of HSU S2 was made equal to the DEM (i.e., the 25 m Provincial Digital Elevation Model).
Root mean square error (after deterministic grid alterations): n/a
The RMSE compares how similar interpolated grid values are to the original input data. In the case of HSU S2, the RMSE is not reported because the top of HSU S2 was made equal to the DEM.