Drainage networks and watersheds delineation derived from TIN-based digital elevation models

• Ano de defesa: 2014
• Autor(a) principal: Henrique Rennó de Azeredo Freitas
• Orientador(a): Corina da Costa Freitas, Sergio Rosim
• Banca de defesa: Rafael Duarte Coelho dos Santos, Wilson Cabral de Sousa Júnior
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Instituto Nacional de Pesquisas Espaciais (INPE)
• Programa de Pós-Graduação: Programa de Pós-Graduação do INPE em Computação Aplicada
• País: BR
• Link de acesso: http://urlib.net/sid.inpe.br/plutao/2014/11.16.19.25

Digital Elevation Models (DEMs) are objects of great importance in many studies of natural sciences and one relevant area of their application is hydrology, as from a DEM it is possible to generate drainage networks and watersheds, which are essential elements in the understanding of hydrological processes. All the methods developed to generate drainage networks from a DEM depend on its representation and the most common representation is given by regular grids, where elevation values are assigned to cells uniformly distributed over space. However, this representation presents limitations in the flow directions, which are defined in only eight distinct directions. This work considers the terrain model given by a Triangulated Irregular Network (TIN) generated from contour lines and sampled points, where the terrain surface is modeled by several triangles defined from a set of points adequately distributed over space, so that the TIN can efficiently adapt to its irregularities. In addition, flow directions on TINs encompass a11 the possible directions and depend on the slope of the triangles, so this structure is more flexible regarding the calculation of water flows. The triangulation used in this work is the constrained Delaunay triangulation and the method that generates drainage networks considers flow directions given by the gradient of the plane defined from each triangle. Problems that commonly occur in DEMs such as flat areas and pits, which create inconsistencies in the terrain model and discontinuities in flows, also deserve special attention. In the present work, flat areas are removed by the insertion of new points into the triangulation with interpolated elevation values and pits by the definition of paths of points starting from the pit until reaching another point of lower elevation, where all these points have their elevation values re-interpolated. Most importantly, this work describes a methodology for calculating drainage paths from a TIN traced by processing the triangles with an associated priority and then connected defining a drainage graph structure, which is proposed in this work for the calculation of accumulated flows. Afterwards, drainage networks are generated according to given threshold values and watersheds are then delineated from the drainage networks. A11 the results from the TIN are qualitatively compared to regular grid results generated with the TerraHidro computational platform developed at INPE and also to an available drainage network produced by specialists and considered here as a reference of the main courses of water over the terrain. Results are very promising showing that TIN terrain models can be used to generate drainage networks from accumulated flows consistent with real-world hydrological patterns.