An integrated algorithm to evaluate flow direction and flow accumulation in flat regions of hydrologically corrected DEMs

Hongming Zhang, Zhihong Yao, Qinke Yang, Shuqin Li, Jantiene E.M. Baartman, Lingtong Gai, Mingtian Yao, Xiaomei Yang*, Coen J. Ritsema, Violette Geissen

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

16 Citations (Scopus)


In order to conduct an accurate hydrological analysis of a watershed, certain conditions need to be understood. Flow direction and flow accumulation are important watershed characteristics that need to be determined before an analysis can be made. Other important characteristics which can be gleaned from analysing the digital elevation model (DEM) of a watershed include channel networks, stream lengths and watershed boundaries. Determining flow direction and flow accumulation is usually carried out in separate steps. Flat regions are types of terrain in raster DEMs without local elevation gradients. Evaluating flow direction and flow accumulation in flat regions using DEMs is a well-known problem in watershed analysis because of the occurrence of problematic parallel flow lines. Calculations also tend to be time-consuming. We have developed an efficient and comprehensive integrated approach to assign flow directions and flow accumulation in flat regions. This approach uses values for non-flat flow accumulation and a maze algorithm with a weight value (MW method) to determine several things: a main flow line through the flat area to the local outlet, an octree tree, and first-in first-out queue structures to calculate flow accumulation. The MW method can be applied to hydrologically corrected DEMs and a single flow path can be provided to resolve all flat areas. To investigate the influence on the topological properties of the channel networks, we used this integrated algorithm to extract three sets of flow accumulation areas from existing DEMs. Using this new integrated method was faster than using the two existing methods and produced continuous channel networks without the occurrence of problematic parallel flow lines.

Original languageEnglish
Pages (from-to)174-181
Publication statusPublished - 2017



  • Channel networks
  • Flat area
  • Flow accumulation
  • Flow direction
  • Hydrology

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