Sergio Rosim

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

Triangulated Irregular Networks (TIN) efficiently define terrain models from which drainage networks and watersheds can be extracted with important applications in hydrology. In this work, the TIN model is represented by a constrained Delaunay triangulation obtained from contour lines and sampled points. Paths of steepest descent calculated from the TIN are connected by processing the triangles according to an associated priority, then forming a drainage graph structure proposed to generate drainage networks from accumulated flows. Major problems such as flat areas and pits that create inconsistencies in the terrain model and discontinuities in flows are removed with procedures that interpolate the elevation values of particular points on the TIN. Drainage networks are defined by arbitrary threshold values, and their associated watersheds and subwatersheds are then delineated. TIN results are qualitatively and quantitatively compared to an available reference drainage network, and also to regular grid results generated with the TerraHidro system. The drainage networks automatically obtained from the drainage graph highly agree to the main courses of water on the terrain, indicating that the TIN is an attractive alternative terrain model for hydrological purposes, and that the proposed drainage graph can be used for the automatic extraction of drainage networks that are consistent with real-world hydrological patterns. HighlightsAn algorithm to generate a drainage graph structure from a TIN model is proposed.The drainage graph allows to derive drainage networks from accumulated flows.An improvement on the procedure for removing flat areas from TINs is presented.Drainage networks and watersheds are consistent with real-world drainage patterns.The algorithms developed are computationally efficient with linear-time complexities.

Terrahidro — A Distributed Hydrological System to delimit large basins

This paper describes TerraHidro that is a distributed hydrologic modeling platform. TerraHidro is general purpose water resources system that presents a new concept to represent water flows based on graph structure, in the geographic information system (GIS) context. The drainage extractions and Amazonian basin delimitations using TerraHidro have been compared with ArcGis Hydro Tools regarding to drainage extractions and to show the TerraHidro availability the drainage of Amazonian sub basins, called Xingu, Purus and Tapajos are presented.

Drainage network extraction of Brazilian semiarid region with potential flood indication areas

This region has the particularity of, at the same time, coexisting with sporadic floods and scarcity of water. This situation requires complex studies involving water resources based on runoff of rain waters and on the courses of the rivers. For the extraction of drainage was carried out by using of the system for hydrological modeling treatment TerraHidro, developed by INPEs Image Processing Division. This system uses the PFS method for extraction of drainage, which has provided good results, enabling the reduction of the time spent on manual editing of drainage errors. TerraHidro has a tool called Height Above the Nearest Drainage (HAND) which gives information on potential flood areas. Elevation data were used in the Aster GDEM with spatial resolution of 30 meters for drainage extraction. A qualitative comparison was performed between drainage extracted by TerraHidro and drainage manually extracted by a specialist.

Delimitation and Analysis of Environmental Protection Areas in the Paraíba do Sul River Basin in Brazil

This work establishes a semi-automatic methodology to define and evaluate the Environmental Protection Areas (EPA), in the Paraíba River Basin, Brazil, taking account the land use and the water quality. The development of this work started from the water capitation point of Guaratingueta city located on the stream that runs through the city. From ASTER GDEM data the drainage network and the basin catchment was automatically extracted. Landsat images for the dates of 1989, 2001 and 2014 were digitally classified and the land uses were mapped, considering the area of permanent protection (APP) for drainage, respecting the limits indicated by Brazilian forest code. Scenes from the RapidEye satellite were used to answer questions of classification, due to good image definition. The study showed that in 1989, the total area classified as APP, 37.59% were anthropized, reaching 37.98% in 2001 and 36.98% in 2014. In a few years it was possible to associate data from water quality, measured directly at the capitation. In 2001 the water quality data showed that the intensive use of fertilizers drained into the Guaratingueta stream by rice paddies was seriously affecting the water supply of the municipality. In 2008 measures for water quality at the capitation point showed that the water resources were still impacted by agricultural activities from the rice fields. So, this work indicates the need for revitalization of the APP inside the EPA Guaratingueta in order to meet the law, protect watersheds and also avoid large investments in water treatment arriving for public consumption.

Terrahydro - A distributed hydrological system using graph structure for unified water flow representation

This paper presents TerraHydro, a Distributed Hydrological System created to develop hydrographic basin water flow GIS applications. TerraHydro proposes a different computational representation for dealing with water flow in GIS applications. These applications involve the concept of local flow, extracted from terrain, which is the basis for most spatially explicit distributed hydrological models. Different computer structures based on regular grids, triangular irregular networks, contour lines, and irregular polygon tessellations have been used to extract local flow, occasioning entirely dependent on the data structure chosen for terrain representation. Then, each local flow set requires its own specific extraction algorithms, as well as different formats to store its associated local flow. TerraHydro proposes a data structure based on Graph Theory that unify computer local flow representation, independent of the data structures used for terrain representation permitting that a set of operations for water management can be formally defined over this new structure.

Urban Flood Area Delimitation Using Reverse Water Local Flow Paths

South America is vulnerable to flood disasters, which must be prevented and managed, especially in the urban area close to the rivers. Different terrain descriptors (e.g. hydrographic network, altimetry) are taken into consideration to identify area with potential risk of flooding. INPE has developed tools to process and manage hydrological information. This paper aims to improve such tools proposing a method to study urban flood area delimitation starting from a raster elevation representation of the urban area with high resolution and water level information. In particular, the proposed method considers the water behaviour assuming that water flood happens in the part of the river having altimetry higher than the surrounding surface. The use of such water behaviour information results in the improvement of the accuracy of the study of urban area with risk of flooding.

Drainage Network Definition for Low Resolution DEM Obtained from Drainage Network Extracted from High Resolution DEM Using Upscaling Processes

Drainage network is basic information for developing applications involving surface and underground water resources. The determination of good quality drainage network can be extracted from altimetry grids with high or at least medium resolution. They can be used for studies in small and large watersheds. When the target is a large watershed, high and medium resolutions are not adequate. The grid resolution should be decreased and consequently the drainage network must be extracted for this new resolution. This mapping can be done in two ways. The first possibility is to extract the drainage network from the new grid altimetry. The second one is to define the new drainage network from the original drainage. In this work, the second possibility was implemented to provide the best quality drainage. The method called Priority First Search—PFS used by TerraHidro for extracting drainage from Shuttle Radar Topography Mission (SRTM) with 90 m of horizontal resolution, is described. The Upscaling process, responsible to convert high resolution drainage network to low resolution drainage network, is detailed and results are presented to show the effectiveness of the Upscaling process contained in TerraHidro. The distributed hydrologic models employed in underground waters using in many cases the network of surface drainage as basic information.

Delimitation of permanent protected areas of rivers in Brazil

This paper presents a methodology to determine the permanent protected areas (PPA) of the the riverbanks. The amount of protected area depends on the river width and the size of each property which have a river running through or by it, as stated in the Brazilian forest code law. The rules are: 30 meters for rivers up to 10 meters wide, 50m for rivers 10 to 50m wide, 100m for rivers 50 to 200m wide, 200m for rivers 200 to 600m wide, and 500m, to rivers wider than 600m. The steps to determine the PPA buffer along the river are (1) construction of the triangular grid (TIN) that constitutes the basis for the calculation of the central axis of the river; (2) definition of the points representing the central axis of the river, called skeletonization; (3) definition of the river width; (4) calculation of the buffer for each river segment. PPA is defined by overlaying the river protected area polygon with the property polygon. A PPA area of a property can be reduced according to its size and according to public improvements like roads, permanent protected areas, for example. At the end the area to be preserved in a property is delimited.