High-resolution digital elevation models (DEMs) offer opportunities for channel network extraction due to its representation of realistic topography. Channels are generally surrounded by well-defined banks that have a distinct signature in the contour lines. Contour curvature is one of the important topographic attributes usually used for channel head identification; however, the curvature at channel heads may vary considerably between and even within watersheds. Therefore, uncertainty exists in the extracted channel heads due to the specified curvature threshold. In this paper, the locations of channel heads in 14 small mountainous watersheds are obtained using a nonparametric method based on the shape of contour lines generated from DEMs with a spatial resolution of 1 m, and the channel head curvature is computed from the extracted channel heads. The spatial distributions of the channel head curvature in these 14 watersheds have been analyzed, and another two watersheds with field-mapped channel heads are selected for validation. The results indicate that: (1) the channel head curvature is sensitive to the local terrain and varies within and between watersheds; (2) the Gamma distribution effectively fits the spatial distribution of the channel head curvature in all the selected watersheds; and (3) constant threshold-based methods for channel head identification gain significant location errors even within a single watershed.

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