Effect of DEM grid size on microrelief indexes estimation for sloping lands after reservoir tillage

Abstract

In many studies, the role of tillage-induced surface microrelief (TSM) in water erosion was assessed by comparing the changes in microrelief indexes during rainfall estimated from a digital elevation model (DEM). Accurate quantification of microrelief indexes is essential because it was said that DEM resolution affects microrelief indexes. The objective of this study was to estimate several common microrelief indexes (tortuosity index (TB), maximum depression storage (MDS), depression volume, depression area ratio and surface microrelief slope) and determine how DEM resolution affects these indexes. Surface elevation data of three surface slopes were collected using a laser scanner from 1-m-wide by 2-m-long plots after reservoir tillage. A series of DEMs with grid sizes of 1, 2, 4, 6, 8, 10, 20, 40 and 60 mm were generated based on the interpolation method. Our results showed that TB decreased with increasing grid size, while no significant differences were measured among the small grid sizes; overall, the MDS and depression volume remained steady regardless of DEM grid size, meaning that the effects of grid size on the MDS and depression volume are very small; the depression area ratio decreased with increasing grid size. As the grid size increased, the number of steep slopes decreased, while gentle and medium slopes exhibited increasing surface microrelief slopes. Therefore, on reservoir tillage-treated slopes, the effects of grid size on microrelief indexes differed due to their different physical meanings. Based on our results, it is better to maintain a grid size of 20 mm or smaller when estimating DEM-based microrelief indexes.