GIS-evaluation of two slope-calculation methods regarding their suitability in slope analysis using high-precision LiDAR digital elevation models

✍ Scribed by M. Irfan Ashraf; Zhengyong Zhao; Charles P.-A. Bourque; Fan-Rui Meng

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 722 KB
• Volume: 26
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/hyp.8195

✦ Synopsis

Slope is a metric that is essential to describe surface hydrological processes, including overland flow, soil erosion, and sediment transport. Most commercial GIS have built-in functions to calculate the slope from Digital Elevation Models (DEMs) by means of average neighbourhood methods that are appropriate for coarse-resolution DEMs. Emergence of high-resolution DEMs from LiDAR data creates a need to re-assess the suitability of existing algorithms for calculating slope in hydrological applications.

In this study, we investigate the properties of two different slope-calculation methods: an average-neighbourhood-slope (ANS) and a downhill-slope (DHS) method. Conceptually, the DHS method provides a more intuitive description of surface water-flow characteristics in an uneven terrain. DEMs of five different types were used to evaluate the methods, namely a 1-m and 10-m resolution DEM interpolated from irregular elevation point-data generated with conventional photogrammetric techniques, and a 1-m, 5-m, and 10-m resolution DEM derived from LiDAR data. The slopes calculated were summarized for the entire watershed, along mapped streams, and within pre-defined 'stream buffers'. Slopes generated for the entire watershed with 1-m resolution LiDAR DEM indicated that the ANS method on an average produced smaller slopes than the DHS method (0Ð64 °). A similar trend was observed in stream buffers, with greatest slope differences (S) between methods within 20-m buffers, when the 1-m LiDAR-based DEM was used (S D 1Ð12 °). In contrast, the ANS-calculated slopes along mapped streams were generally larger than those calculated with the DHS method for LiDAR-based DEMs (S D 0Ð81 °). The results from this study signal the need for caution when estimating slopes along streams from high-accuracy, LiDAR-generated DEMs.