Dataset Dev: Apr 2022 Update

Author: Eric Kessel

After nearly one full year, the C1W team has made incredible progress pulling together the national-scale datasets required to build the HydorGeoSphere models at the heart of the C1W project. In this update we review some of the datasets that have been developed at this stage. Click here to read the previous dataset development update (December 2021).

The groundwater-surface water (GW-SW) model construction is the first of four main groups of datasets for C1W. These include HydroGeoSphere Domains (which delineate the areas covered by each basin scale model), an Elevation-Terrain Model (which defines the topography/surface elevation of each model), a Lake Bathymetry Model (used to define the surface elevation of each model wherever a large lake is present), and a River Network (to delineate major rivers/streams). All four datasets are required for all seven basin scale models, and together they form the C1W conceptual model. Finally, Finite Element Meshes are being developed for each model region, which allow the team to discretize the domain and begin assigning physical properties and boundary conditions to the models, thereby creating a digital twin of each drainage basin.

HydroGeoSphere Domains (Figure 2)

National Hydrographic Network (NHN) watershed boundaries were grouped into 7 major models (Arctic, Baffin, Atlantic, Hudson, Mackenzie, Nelson, Pacific). Some models also include parts of the NHD (USA).

Elevation-Terrain Model (Figure 3)

There is no current national coverage DEM available from Canada, and the Canadian Digital Elevation Model (CDEM) is outdated. Thus, C1W developed a new homogenous DEM which maximizes use of the HRDEM coverage of Northern Canada. The Copernicus DSM was used to fill voids in the HRDEM and extend its coverage into Alaska. The SRTM was used to cover areas south of the N60° in Canada and into the USA. Once harmonized, the C1W DEM was burned with a lake bathymetry model to best represent the true terrain beneath lakes. Ocean bathymetry was also included.

Lake Bathymetry Model (Figure 4)

There is limited lake bathymetry data available for Canada, particularly in northern areas. As such, a lake bathymetry model was built and used to estimate the lake bathymetry for large lakes (>10 km2) within the C1W model domain. The C1W Lake Bathymetry Model using a hierarchy of real and estimated lake bathymetry.

River Network (Figure 5)

The current NHN Network Linear Flow (NLFLOW) network does not have stream order attributes for the nation-wide dataset. As such, C1W has processed the NHN to add Strahler Stream Order to the attributes, which allows us to refine the drainage network to the desired resolution for HGS (≥4 and ≥5 Strahler for Fine and Coarse mesh resolution, respectively). The USGS National Hydrological Dataset (NHD) has Strahler stream order assigned to the USA south (NHDPlus), however not for Alaska. Therefore, the NHD for Alaska was also processed to attribute Strahler order.

Finite Element Mesh (Figure 6)

C1W will utilize two finite element (FEM) meshes for HGS for each model domain; a coarse and fine resolution FEM using ≥5 and ≥4 Strahler Order Streams, respectively. Anticipating 8 total nodal sheets in each model, the node count targets for a single 2D mesh sheet are <65,000 and <125,000 nodes for the coarse and fine resolution meshes, respectively. Coarse resolution meshes are already completed (Figure 6). Preliminary fine resolution meshes are currently being working on.

Figure 5. Strahler Order 5 and greater stream network for North America unifying the processed NHN and NHD (Alaska) with the pre-existing NHDPlus (USA).

Figure 2. Grouping of NHN and NHD watersheds for model boundaries.

Figure 3. Third iteration of the C1W DEM using Copernicus to void fill artefacts in the Arctic HRDEM with data source footprint illustrated by color (left) and burned with the Lake Bathymetry Model and joined with ocean bathymetry (right). Note that the color scale is non-linear to exaggerate elevation differences in this figure.

Figure 4. Distribution of lakes >10 sqkm color coded to their respective data availability (left) and C1W DEM burned with Lake Bathymetry illustration with lake depth highlighted in color and ground elevation in greyscale (right).

Figure 6. Coarse meshes with Strahler order 5 and greater stream splines color coordinated by connected watersheds (870 total).