Hydrography-Driven Coarsening of Grid Digital Elevation Models

A new grid coarsening strategy, denoted as hydrography-driven coarsening, is developed in the present study. The hydrography-driven coarsening is designed to retain the essential hydrographic features of valleys and channels observed in high-resolution digital elevation models: (1) depressions are filled in the considered high-resolution digital elevation model, (2) the obtained topographic data are used to extract a reference grid network composed of all surface flow paths, (3) the Horton order is assigned to each link of the reference grid network, and (4) within each coarse grid cell, the elevation of the point lying along the highest-order path of the reference grid network and displaying the minimum distance to the cell center is assigned to this coarse grid cell center. The capabilities of the hydrography-driven coarsening to provide consistent surface flow paths with respect to those observed in high-resolution digital elevation models are evaluated over a synthetic valley and two real drainage basins located in the Italian Alps and in the Italian Apennines. The hydrography-driven coarsening is found to yield significantly more accurate valley and channel profiles than existing coarsening strategies. In absolute terms, the obtained valleys and channels compare favorably with those observed. In addition, the proposed coarsening strategy is found to reduce drastically the impact of depression-filling in the obtained coarse digital elevation models. The hydrography-driven coarsening strategy is therefore advocated for all those cases in which the relief of the extracted drainage network is an important hydrographic feature.