What is the optimal digital elevation model grid size to best capture hillslope gullies and contour drains?

Aerial and ground-based survey routinely employs technology such as digital photogrammetry, Light Detecting and Ranging (LiDAR) and Terrestrial Laser Scanning (TLS). These systems produce huge data sets with varying accuracy and reliability. At present there are no guidelines for the grid size dimension needed to accurately and reliably represent common features such as rills, gullies and contour drains. Here, synthetic landscapes with a very high density of points (10,000 pt m⁻²) are created. Coordinate data capture error is also examined. Results demonstrate that for the reliable representation of a gully or contour drain, the DEM grid spacing needs to be at least 1/3 the width of the feature of interest. Typical coordinate errors inherent within the data do not significantly affect the definition of gullies or contour drains. The findings here provide a defensible guide for the coordinate density required to hydrologically and geomorphically represent a landscape surface.