Dataset Dev: September 2022 Update

Author: Eric Kessel

We’ve made tremendous progress in developing the datasets that will be the foundation of the Canada1Water HydroGeoSphere models. Here we review the latest developments we’ve made on the land surface configuration, hydrostratigraphy and model domains in HydroGeoSphere.

Click here to read the previous dataset development update (April 2022)

Land Surface Configuration

We have been preprocessing ground elevation data that will be used to support the finite element mesh development and attribution in HydroGeoSphere. First a homogenized digital terrain model (DTM) with complete coverage of Canada1Water is needed to assign a top elevation to the models. Second, we need to modify this DTM to suppress or eliminate surrounding islands that are within the Canada1Water domain but are intentionally excluded given their hydrological disconnect to the mainland and undesired influence in HydroGeoSphere. 

Offshore Island Removal from Digital Elevation Models

The model domain of Canada1Water extends 50 km offshore. Inclusion of offshore islands in such a large model introduces unnecessary complications in the model mesh development and calculations.  Available DTM products have been preprocessed to remove islands which are offshore but within the 50km coastal buffered areas by setting their elevations to -10 m ASL to eliminate any influence on the models (Figure 1).

Figure 1. Canada1Water DEM with offshore islands flattened to -10mASL. An example on the north coast of Baffin (top right) shows the flattened areas (bottom right).

Hydrostratigraphy

For groundwater modelling it is essential to represent subsurface heterogeneity and layering to support the assignment of appropriate hydraulic conductivity values to porous (aquifer) and nonporous (aquitard) units.  HydroGeoSphere models constructed for the Canada1Water project will include 6 to 8 layers, consisting of 2 soils layers, 2-3 surficial geology layers, and 2-3 bedrock geology layers (Figure 2). The elevation of these layers are constrained by the DTM at the top, soils and geological mapping at or below the surface, and a model basement of -100masl unless bathymetry requires the bottom of the model to go below -100masl. In future newsletters the respective hydrostratigraphic layers assembled for soils, surficial geology, and bedrock will be previewed.

Figure 2. Conceptual hydrostratigraphy for Canada1Water models illustrating the number of layers to be included in the HydroGeoSphere models. Note the relative thicknesses of surficial and bedrock geology vary between models, but the soil layers are the same thicknesses.

Model Domains Update

Canada1Water initially considered dividing the continental domain and Baffin Island into 6 large oceanic and watershed defined domains. Subsequently, recognizing the unique physiography, geology, permafrost conditions, and size of Baffin Island it was decided to model Baffin Island separately from the Arctic Domain (Figure 3). Baffin Island now forms its own island domain of 800,000 square kilometres. The Canada1Water models continue to include approximately 1.3 million square kilometres of transboundary watersheds that occur in the United States (0.4 million and 0.9 million square kilometers in Alaska and below Canada/USA border, respectively). 

Figure 3. Canada1Water 3D Visualization of HydroGeoSphere models.

Bringing together the updates to the C1W model domains, the latest digital terrain models representing the upper model elevation, and the proposed hydrostratigraphy, we present an early 3D representation of the Mackenzie River Basin model in Figure 4. In the upper and lower-left panel we see elevations ranging from approximately 3000-4000 mASL along the Western edge of the model representing the Eastern slopes of the Rocky Mountains. In the lowlands we can also see depressions in the landform representing Lake Athabasca, Great Slave Lake and Great Bear Lake. The lower panels of Figure 4 illustrate the distribution of model layers for the Mackenzie River Basin model (note: Inset 2 only illustrates 6 of 7 model layers, with a 2nd bedrock layer being present beneath those shown in the inset).

Figure 4. Mackenzie 3D Model showing the coarse mesh resolution and 7 layer hydrostratigraphy. This depth to bedrock is approximated but will be improved with a depth to bedrock map for C1W.

Continue to monitor this space for further updates to the core datasets that form the foundation of the Canada1Water HydroGeoSphere modelling efforts!