NetMap Synthetic ("Smart") River Networks
How is a synthetic river network (stream layer) built?
Critical drainage area is drainage area per unit contour length and various thresholds can be used to identify provisional locations of channel heads or channel extent (Figure 1). Critical area is equal to area multiplied by slope gradient-squared (AS2). Threshold values vary with steep and less steep topography, for example, less than 25%, greater than 25% etc. Plan curvature is the curvature of the surface on a cell-by-cell basis, as fitted through that cell and its eight surrounding neighbors. Curvature is the second derivative of the surface, or the slope-of-the-slope. The plan curvature is perpendicular to the direction of the maximum slope (Figure 2). Algorithms for flow direction and channel delineation are described by Clarke et al. 2008 but see latest Technical Help.