Digital Data 2018-0001
In 2018 the Alberta Geological Survey (AGS) updated its digital data (shapefile) of bedrock valley thalwegs to include the addition of more than 1350 new valley thalwegs. The shapefile includes fifteen fields of descriptive information, including references to the sources of data collected over more than 50 years at AGS. These attributes enable the user to query thalwegs based on age, nature of valley exposure, genesis of valley, the catchment stream/valley, and the depositional basin.
Unlike previous maps and digital datasets, thalwegs captured in this shapefile are not just those of buried bedrock valleys, or valleys of preglacial age, but include all valleys incised into bedrock including valleys of present-day rivers that have downcut into bedrock. In this last case, incision to bedrock was verified by locating exposures of bedrock from high-quality Google Earth imagery.
AGS has attempted to preserve the traces of historical work, altering or omitting thalwegs only where new information shows either the presence, or the position, to be invalid. Very few edits were made of this nature.
As a result of an initiative in 2018-2019 to update the bedrock topography map of Alberta, new mapping in the northern part of the province (Peace River to Fort McMurray) supported the addition of a few new thalwegs and edits of a few previously defined thalwegs to the current shapefile in 2019.
Andriashek, L.D., comp. (2018): Thalwegs of bedrock valleys, Alberta (GIS data, line features); Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Digital Data 2018-0001.