Evaluation of flow direction methods against field observations of overland flow dispersion

• Published in: Water resources research Vol. 48; no. 10
• Main Authors: Orlandini, Stefano, Moretti, Giovanni, Corticelli, Mauro A., Santangelo, Paolo E., Capra, Alessandro, Rivola, Riccardo, Albertson, John D.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.10.2012; John Wiley & Sons, Inc
• Subjects: Average flow; Experimental methods; flow direction methods; Flow pattern; gridded elevation data; Heat detection; Lasers; Methods; Overland flow; planar dispersion; terrestrial laser scanner; thermal imaging camera
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2012WR012067

The D8, D8‐LTD, D∞‐LTD, D∞, MD∞, and MD8 flow direction methods are evaluated against field observations of overland flow dispersion obtained from novel experimental methods. Thin flows of cold water were released at selected points on a warmer slope and individual overland flow patterns originating from each of these points were observed using a terrestrial laser scanner and a thermal imaging camera. Land microtopography was determined by using laser returns from the dry land surface, whereas overland flow patterns were determined by using either laser returns or infrared emissions from the wetted portions of the land surface. Planar overland flow dispersion is found to play an important role in the region lying immediately downslope of the point source, but attenuates rapidly as flow propagates downslope. In contrast, existing dispersive flow direction methods are found to provide a continued dispersion with distance downslope. Predicted propagation patterns, for all methods considered here, depend critically on the size h of grid cells involved. All methods are found to be poorly sensitive in extremely fine grids (h ≤ 2 cm), and to be poorly specific in coarse grids (h = 2 m). Satisfactory results are, however, obtained in grids having resolutions h that approach the average flow width (50 cm), with the best performances displayed by the MD8 method in the finest grids (5 ≤ h ≤ 20 cm), and by the MD∞, D∞, and D∞‐LTD methods in the coarsest grids (20 cm < h ≤ 1 m). Key Points Laser scanners and thermal imaging cameras can detect overland flow patterns Overland flow dispersion rapidly attenuates as flow propagates downslope Grid cell size strongly affects modeled overland flow dispersion