An improved method for single flow direction calculation in grid digital elevation models

Abstract

This paper presents improvements to the global D8 (GD8) method for calculating single flow directions in a grid digital elevation model. Flow directions computed from grid digital elevation models serve as the foundation for much of the analysis and modeling of hydrological processes that are driven by topographic gradients. The literature includes both single flow direction methods, where flow goes to only one downslope cell, and multiple flow direction methods that apportion flow among multiple downslope cells. Among single flow direction methods, the standard D8 method, in which the flow direction is set based on the steepest local slope, results in bias on surfaces that do not align with the grid directions. Efforts to address this problem have led to the development of extended methods that account for elevation values further upslope in determining flow directions. We have identified discrepancies in one such method, GD8, and have examined ways to resolve these discrepancies. An improvement to GD8, named iGD8, is presented that allows replacing a reference cell from which path deviations are accumulated and that considers horizontal path deviation rather than global slope as a flow direction criterion. The improved method is found to be effective in resolving the problems encountered with GD8 and to be more efficient than a previously proposed alternative method (least transversal deviation (LTD) based D8, namely D8‐LTD) that uses recursive searching for the largest upstream area when multiple flow paths converge. The proposed improved GD8 method offers the opportunity for improved analysis and modeling of topographically driven hydrological processes by providing better foundational flow directions for these analyses.

High‐Resolution Modeling of Reservoir Release and Storage Dynamics at the Continental Scale

“…On the contrary, when a smaller basin area is assigned to a reservoir, which should have had a larger basin area, underfilling and excessively underestimated release can be caused. These are inevitable problems in high‐resolution surface water modeling using raster grid flow direction maps that determine the direction of flow from a grid cell to its downstream among eight directions (i.e., four in cardinal and four in diagonal directions) even though, in reality, surface water can flow in any direction (see Shin & Paik, , and references therein). In this study, we resolve these issues by comparing the drainage area at a reservoir location estimated by the model with that obtained from GRanD database.…”

“…In particular, distortions in topography slopes in SRTM DEM and other inconsistencies in error removal method have been improved in MERIT DEM; hence, MERIT DEM is suitable especially for terrain-dependent hydrologic applications such as reservoir-floodplain simulations (Yamazaki et al, 2017). In principle, the flow direction results from one DEM is not applicable to another DEM, hence the use of MERIT DEM requires the retrieval of flow directions that can be conducted by various automated methods (e.g., Shin & Paik, 2017), however manual corrections are essential, which involve tedious and laborious tasks for , and b the rasterized maximum reservoir extent of Lake Sakakawea in the Missouri river shown by a cyan box in (a). The color coding in (b) represents the fraction of GRanD reservoir extent within LHFD grid cells.…”

Simulating the evolution of the topography-climate coupled system

“…For this study, we revised and upgraded the source code of LEGS, adopting many improved features. One of them is the replacement of GD8 with the improved GD8 method (Shin and Paik, 2017), which resolves known technical issues of the original GD8. The improved GD8…”

Nondispersive Drainage Direction Simulation Based on Flexible Triangular Facets

“…However, both D8-LTD and iGD8 correct its final drainage direction by taking account of the bias between the D∞ directions of local cells and their eight possible directions along only one uniquely designated path. For instance, while adjusting the direction for a cell where multiple paths converge, only the bias of the pathway with the largest upstream drainage area for the given cell is adopted by D8-LTD (Orlandini et al, 2003), while iGD8 merely considers the path of the source cell with the highest altitude (Shin & Paik, 2017). That is to say, only partial information from upstream can be used in the determination of drainage directions.…”