Hydrologic Terrain Processing Using Parallel Computing

Abstract: Topography in the form of Digital Elevation Models (DEMs), is widely used to derive information for the modeling of hydrologic processes. Hydrologic terrain analysis augments the information content of digital elevation data by removing spurious pits, deriving a structured flow field, and calculating surfaces of hydrologic information derived from the flow field. The increasing availability of large terrain datasets with very small ground sample distance (GSD) poses a challenge for existing algorithms that process terrain data to extract this hydrologic information. This paper will describe a parallel algorithm that has been developed to enhance hydrologic terrain pre-processing so that larger datasets can be more efficiently computed. This paper describes a Message Passing Interface (MPI) parallel implementation for Pit Removal. This key functionality is used within the Terrain Analysis Using Digital Elevation Models (TauDEM) package to remove spurious elevation depressions that are an artifact of the raster representation of the terrain. The parallel algorithm works by decomposing the domain into stripes or tiles where each tile is processed by a separate processor. This method also reduces the memory requirements of each processor so that larger size grids can be processed. The parallel pit removal algorithm is adapted from the method of Planchon and Darboux that starts from a large elevation then iteratively scans the grid, lowering each grid cell to the maximum of the original elevation or the lowest neighbor. The MPI implementation reconcile

Capabilities and limitations of laser scanning system altimetrics informations applied in an urban settlement

A concentração da população brasileira residindo em ambientes urbanos demandam uma gestão eficiente do território e dos efeitos provenientes do escoamento hídrico, tais como erosão, inundações e movimento de massa. O presente trabalho tem como objetivo adequar para áreas urbanas a delimitação de Áreas de Sensibilidade Hidrológicas (ASH), utilizando o Índice Topográfico de Umidade (ITU). A área de estudo é a Região Administrativa de São Sebastião do Distrito Federal que apresenta expansão urbana recente e problemas de drenagem urbana. A pesquisa discute as potencialidades e limitações quanto à utilização de dados altimétricos provenientes de laser na derivação de Modelos Digitais de Elevação (MDE) e na estimativa do escoamento superficial. A aplicação do índice HSA em áreas urbanas necessita de metodologias específicas: redução da nuvem de pontos amostrais pela seleção de fatores relevantes para o fluxo da água, filtragem de artefatos, manutenção das feições urbanas que condicionam o direcionamento hídrico, eliminação da cobertura vegetal, dentre outros. Os resultados obtidos mostram o potencial de estabelecer áreas sensíveis dentro da rede urbana com alta precisão, considerando as influências da topografia local. Portanto, a pesquisa inova ao apresentar uma solução metodológica de estimativa de HSA para o ambiente urbano na escala local.The concentration of the Brazilian population living in urban environments requires efficiently manage the territory and the effects of water runoff, such as erosion, floods, and mass movement. This work aims to adapt the delimitation of Hydrological Sensitivity Areas (HSA) to urban areas, using the Topographic Wetness Index (TWI). The study area is the Administrative Region of São Sebastião, in the Federal District, which presents recent problems of urban expansion and urban drainage. The research discusses the potentials and limitations in the use of altimetric data from the laser profile in the derivation of Digital Elevation Models (DEM) and the estimation of surface runoff. The application of the HSA index in urban areas requires specific methodologies: reduction of the sample point cloud by the selection of relevant factors for the flow of water, filtering of artifacts, maintenance of urban features that condition the direction of the water, elimination of vegetation cover, among others. The results obtained show the potential to establish sensitive areas within the urban network with high precision considering the influences of the local topography. Therefore, the research nnovates by presenting a methodological solution to estimate HSA for the urban environment at a local scale

Parallel Flow-Direction and Contributing Area Calculation for Hydrology Analysis in Digital Elevation Models

This paper introduces a set of parallel algorithms to determine the hydrological flow direction and contributing area of each cell in a digital elevation model (DEM) using cluster computers in an MPI programming model. DEMs are partitioned across processes relevant to the physical layout of the terrain such that processes with adjacent ranks calculate flow direction and contributing areas for physically adjacent partitions of the DEM. The contributing area algorithm makes use of a queue to order the consideration of cells such that each cell is visited only once for calculation and cross-partition calculations are handled in an efficient and order-independent manner. This algorithm replaces a serial recursive algorithm included as part of the TauDEM hydrology analysis package

Continental-scale high-resolution river geometry and real-time inundation mapping

Flooding is the most threatening natural disaster worldwide considering the fatalities and property damage it causes. Recent flood disasters have raised concerns for accurate and responsive inundation forecast due to the rapid spread and astonishing destructive power of these events. Although recent development in large scale hydrologic simulation has enabled the real-time streamflow simulation operating on millions of river reaches, a framework for converting the forecast discharge into corresponding water surface elevation and inundation maps at a continental-scale is absent to better support local flood response. To accurately map flood inundation extent, a comprehensive description of the geometry of the channel is indispensable. As such, this dissertation presents an innovative approach for estimating river geometry and conducting inundation mapping at a continental-scale with a high spatial resolution. This approach is based on the concept of Height Above Nearest Drainage (HAND). Advanced hydrologic terrain analysis workflows have been designed to derive channel hydraulic properties, stage-discharge rating curves, and inundation extents using HAND. After the mechanism being presented, the implementation of this approach across the contiguous United States has been demonstrated using the 10-meter National Elevation Dataset. The integrity of the outputs has been validated through the comparison with best available references at multiple test sites. Considering the increasingly availability of high-resolution topographic data derived from lidar technology, the dissertation further presents how advanced geomorphic feature extraction tools are integrated into the proposed approach to overcome the challenges associated with the enrichment of terrain details. At last, this dissertation presents how banklines, an essential piece of river geometry characteristic as the boundary differentiates channel zone from floodplain, is detected with enhanced geomorphic feature extraction tools for improving large-scale hydrologic simulation and inundation mapping accuracy.Civil, Architectural, and Environmental Engineerin

Metodologia de delimitação das unidades hidrográficas no âmbito do Distrito Federal

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Humanas, Departamento de Geografia, Programa de Pós-Graduação em Geografia, 2012.O Brasil possui uma vasta e rica rede de drenagem cujos recursos hídricos são utilizados para os mais diversos fins, tais como uso urbano, industrial, agropecuário, dentre outros, constituindo-se num bem de domínio público, dotado de valor econômico e natureza limitada (Lei no 9.433/97, art. 1o , I e II). Sendo assim é de suma importância priorizar sua eficiente gestão a fim de garantir a devida disponibilidade quali-quantitativa às gerações futuras. Com isso, a própria Lei das Águas (Lei no 9.433/97, art. 1o , V) preconiza a bacia hidrográfica como unidade territorial de implementação das ações do mencionado diploma. Limitando-se ao contexto espacial do Distrito Federal, o objetivo desse trabalho foi propor um método de delimitação das Unidades Hidrográficas (UH’s), com base em técnicas de geoprocessamento e comparar com o atual e vigente mapeamento das UH’s do Distrito Federal, cujo enfoque era mostrar as limitações e potencialidades do método ora proposto. Essas citadas UH’s são provenientes do Mapa das Unidades Hidrográficas do DF, elaborado pela extinta Secretaria de Meio Ambiente, Tecnologia e Ciência – SEMATEC em parceria com a Companhia de Planejamento do Distrito Federal – CODEPLAN, em 1994. A metodologia de trabalho pode ser dividida em 4 (quatro) momentos: (a) Edição e ajustes dos dados vetoriais altimétricos; (b) Elaboração do Modelo Digital de Elevação (MDE), utilizando o algoritmo Topogrid (HUTCHINSON, 1989) e subsequente etapa de consistência hidrológica (MDEHC); (c) Validação da acurácia posicional altimétrica relativa do MDEHC; (d) extração automatizada das áreas de drenagem e compartimentação vetorial das 36 Unidades Hidrográficas, segundo o material cartográfico de referência. A utilização de MDE como parte integrante do fluxo metodológico visa possibilitar a derivação dos modelos de estimativa do fluxo direcional superficial da água no terreno, e com isso dar maior acurácia no traçados dos divisores d’água. Assim nesse trabalho foi conduzida uma discussão a respeito do método direcional de fluxo D8 e Dʿ em relação ao objeto pesquisado, sendo que o primeiro mostrou melhores resultados para a finalidade de delimitação das UH’s de interesse. A comparação entre as UH’s delimitadas segundo o modelo altimétrico e as relativas ao mapa de referência adotado mostraram, inicialmente, coerência em relação aos valores médios absoluto (5,03 Km2 ) e relativo (3,71%) referente ao cálculo de área, porém apresentaram discrepâncias pontuais com relação a forma das mesmas. A importância dessa dissertação remete à otimização das políticas públicas de gestão dos recursos hídricos, principalmente no escopo do planejamento e ordenamento territorial. Assim, também foi realizado uma comparação entre as UH’s elaboradas e o traçado das atuais Regiões Administrativas (RA’s). Observou-se que ocorriam discrepância entre as mesmas, situação desfavorável a gestão dos recursos hídricos. _______________________________________________________________________________________ ABSTRACTBrazil has a vast and rich natural drainage network and this water resource has been utilized for numerous and varied uses, for example: urban use, industrial, farming/ livestock, and other. This Brazilian natural resource has a public domain, with monetary value and is therefore covered under the Legal aspects on Brazilian land use and water law (Law no 9.433/97, art 1o , I e II). It is therefore extremely important to prioritize it’s efficient management to enable the outstanding quali-quantitative availability of this precious natural recourse for the future generations. The Water’s Law, denotes the watershed boundaries’ and uses these boundaries as a territorial land unit to enable the implementation of the prescribed actions for water usage in the above mentioned law. With regard to Distrito Federal’s limits, the aim of this study is to propose a method that’s defines the ydrographic Units (HU’s) using geoprocessing techniques and furthermore compare these HU’s to those actually used on Distrito Federal’s Hydrographic Units map. Those HU’s had came from “Mapa das Unidades Hidrográficas do DF”, created by Scientific, Technologic and Environmental secretary (SEMATEC) and it’s partner Distrito Federal Planning Company (CODEPLAN), prior to1994. The methodology of this study can be subdivided into stages: (a) Editions and adjustments to existing altimetry vetorial data; (b) Digital Elevation Model (DEM)’s generation using Topogrid’s algorithm (HUTCHINSON, 1989) following by hydrological consistency and elaboration of hydrologically corrected DEM (MDEHC); (c) Validation of the relative altimetry position accuracy considering the corrected DEM generated; (d) Automatized Drainage areas’ extraction and delineation of the 36 HU’s according to reference cartography material used in this study. The main use of DEM in this paper study is to gain the best possible altimetry derivations including a flow direction and flow accumulation grid that describes the water’s superficial behavior onto the landscape. Therefore this study has brought forwards a discussion regarding the use of D8 and Dʿ to estimate flow direction grid. The first study had shown better results when compared with the second one, considering the HU’s delimitation of interest. The comparation between HU’s from both products (MDEHC and SEMATEC/CODEPLAN’s reference map) has shown coherence if you consider absolute standard value (5,03 Km2 ) and relative one (3,71%) related to area calculation, nevertheless those ones have shown differences between their polygonal forms. The relevance of this research is to determine and optimize the public policies about water resource management in Brazil, mainly due to sustainable planning and ordering in territorial’s anthropic occupation. So, those UH’s were compared with the Administrative Regions (RA’s) of Distrito Federal and it was realized that there were difference between the form of both, situation not favorable to water resource management

A new spatial basis for rivers monitoring and management in Cyprus

Shortcomings of river typology, river water body network and water body assessment grouping were identified to impede the Water Framework Directive’s (WFD) implementation in Cyprus. A new spatial basis for river monitoring and management was elaborated to alleviate these problems. A stream definition threshold determined from topographical maps and a 20x20m DEM were used for the stream definition process. Consistent quantitative and WFD compliant criteria were applied to identify the new WFD stream network. A new river typology based on the Temporary Stream Regimes of Gallart et al. (2012) was elaborated and comprises four types covering the entire flow permanence gradient (perennial – intermittent - ephemeral/episodic). The applicability of biological monitoring for WFD purposes is exactly specified for each type. For mapping the types onto the stream network, a tiered approach allowed employing the most reliable stream type predictor for each river reach. For ungauged stream reaches, relationships between stream types and catchment characteristics were established and a multi-criteria methodology for assigning types to reaches was developed and applied. The resulting stream network comprises 14% perennial and 86% temporary stream reaches. It represents the first mapping of temporary flow regimes onto a Cyprus-wide river network. Subsequently, water bodies were delineated considering location and spatial extent of pressures, differences in water status and protected areas. Monitoring sites’ ecological status was related to pressures, and thresholds for three pressure levels (negligible, minor, significant) were determined and used to develop an indicator allowing the prediction of pressure levels and related ecological status in water bodies. The new scheme is already being utilized for the elaboration of the second Cyprus River Basin Management Plan. In parallel to the elaboration of the new scheme, anticipated benefits and potential negative effects of the new scheme’s adoption were collected through a stakeholder consultation process, carried out in two action research loops with a total of five consultation sessions. The stakeholders present in the sessions included all significantly involved Government Departments, a contractor and, in the last session, environmental organizations, local Authorities and the general public. Identified benefits are few but significant and refer to improved monitoring, the benefits of the new typology, identified gaps and the developed reusable methodologies. Identified causes for potential negative effects of an adoption of the technical proposal, anticipated mainly in the form of opposition of the European Commission, are the treatment of HMWBs in the assessment groups scheme, the compatibility of the new types with the results of the intercalibration exercise and the fact that the river network is completely new, in comparison to the first RBMP. All these do not bear but small or minimal chances to entail negative effects in practice. Differing views amongst stakeholders about several areas of WFD implementation were also identified. They exist between the stakeholders but also within Governmental Departments and refer e.g. to the “ideal” density of the stream network and the treatment of ephemeral/episodic rivers under the WFD