Hydrologically Conditioned Digital Elevation Model (HDEM)

Description

The Provincial Digital Elevation Model (PDEM) offered by the Ontario Ministry of Natural Resources and Forestry has been up-scaled and conditioned to acquire continuous flow paths. This product is necessary for catchment delineation to any point within the extended ORMGP boundary.

• Type
  • Raster - Gridded on 60m cells.
• Geographic Extent
  • The extended ORMGP Study Area covering the Niagara peninsula to the Bay of Quinty.
• Maintenance Standard
  • Periodically updated in coordination with PDEM updates and by noted flowpath discrepancies discovered by our user base (see Manual Adjustments below).

Georeferencing and Accuracy

• Horizontal Datum
  • North American Datum 1983
• Vertical Datum
  • CGVD2013 (EPSG 6647)
• Ellipsoid
  • GRS 1980
• Prime meridian
  • Greenwich
• Projection
  • Ontario MNR Lambert (EPSG 3161)
• Horizontal Accuracy
  • 1.5m
• Unit
  • metre
• Information source
  • Ontario Ministry of Natural Resources via Conservation Ontario.

Data Sources and Restrictions

• Use Constraint
  • None - in accordance with ORMGP disclaimer
• Citation
  • Oak Ridges Moraine Ground Water Program (2023) Hydro-DEM.
• Agency Originator
  • Oak Ridges Moraine Groundwater Program (ORMGP)
• Agency Distributor
  • Oak Ridges Moraine Groundwater Program (ORMGP)

Methodology

• Data Source - Provincial Digital Elevation Model (PDEM)
  • See source metadata.
• Raster Upscaling
  • PDEM is upscaled from a 30m horizontal resolution to 60m by taking the mean of the 4 intersecting cells.
• Raster Processing

  • Automated depression filling (Wang and Liu, 2006) was applied to the DEM.

  • Flat regions were adjusted according to the depression filling fix of Garbrecht and Martz (1997).

  • Flow paths are computed based on the “D8” algorithm (O’Callaghan and Mark, 1984).

• Manual Adjustments

  • Flow directions are imposed using hand-drawn flow paths where the algorithm fails to discover the true flow direction. Flow paths are save as polyline shapefiles, where its vertices are ordered according to flow direction.

• Derivative Products

  • Cell slopes and slope-aspects are computed using a 9-point planar regression from every cell’s elevation plus its 8 neighbouring grid elevations.
• Replaces or Updates
  • Oak Ridges Moraine Groundwater Program (v2020) HDEM.
• References

  • Garbrecht, J, and L. Martz, 1997. The assignment of drainage direction over flat surfaces in raster digital elevation models. Journal of Hydrology, 193, 204-213.

  • O’Callaghan, J.F., and D.M. Mark, 1984. The extraction of drainage net-works from digital elevation data, Comput. Vision Graphics Image Process., 28, pp. 328-344

  • Wang, L., H. Liu, 2006. An efficient method for identifying and filling surface depressions in digital elevation models for hydrologic analysis and modelling. International Journal of Geographical Information Science 20(2): 193-213.

• Contact
  • email (support@owrc.ca)

Last Modified: 2024-03-24