Effects of Scale on DEM Derived Drainage Networks For a High Arctic Wetland Complex

The ability to automatically generate drainage patterns is a useful tool in hydrologic studies, especially in remote areas where limited data is available. However drainage patterns derived from digital elevation data can be significantly affected by the scale of the data from which they are generated. This study investigates the effects of scaling on drainage patterns extracted from elevation data for a low gradient wetland area on Somerset Island, Nunavut, in the Canadian High Arctic. A series of Digital Elevation Models (DEM's) were created from digitized topographic information at varying resolutions (2.5 m, 5 m. 10 m, 50 m, 100 m, 200 m). Automated drainage network extractions were performed for each resolution grid, using ESRI ArcInfo software. A series of flow networks were created for each resolution DEM using varying minimum stream lengths in order to examine the effects of this variable on flow pattern and direction. The modelled drainage at each resolution was then compared to the `actual' drainage mapped from aerial photography (air photos and low level oblique photographs) and topographic maps to examine differences as a result of scaling. Preliminary results suggest that reproducing correct flow direction was not possible with the coarser resolution DEMs (10 m and up), while the finer resolutions (2.5 m, 5 m) resulted in drainage networks most similar to the mapped drainage.