Digital elevation modelling of soil type and drainage within small forested catchments

Abstract

This paper deals with predicting flow accumulation, drainage class, and soil and vegetation type within small headwater catchments (<20 ha) of two contrasting forested areas in northern New Brunswick, Canada, based on digital elevation modelling. A digital elevation model (DEM), with a point sampling resolution of about 75 m, was used to derive local flow accumulation and slope gradients. These calculations were then compared with direct field mapping of flow accumulation and slope gradients, involving on-site tracking of watershed boundaries, ridges, hummocks, depressions, gullies, and stream channels. In general, the resulting DEM-derived and field-assessed flow accumulation values did not differ statistically from each other. Subsequently, these values were analyzed as potential predictors for soil wetness, drainage, and soil and vegetation type as determined for 77 small forest plots, all scattered throughout the catchments at locations of increasing flow accumulation. In this analysis, the field-assessed flow accumulation values were found to be better predictors than the DEM-derived values . It is suggested that the DEM-derived predictions would be much enhanced by an increased DEM resolution, and that this increase would lead to particularly reliable estimates for local soil wetness, drainage, and soil and vegetation type in catchments with low substrate permeability. Key words: Flow accumulation, soil wetness index, soil taxonomic units, soil drainage, soil permeability, digital elevation model