TERRAHYDRO – a Distributed Hydrological System using Graph Structure for Unified Water Flow Representation. Sergio Rosim Antônio Miguel Vieira Monteiro Camilo Daleles Rennó João Ricardo de Freitas Oliveira National Institute for Space Research - INPE. IGARSS 29/ 07 / 2011. INPE.
29/ 07 / 2011
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, entirely linked to 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 unifies computer local flow representation, independent of the data structures used for terrain representation permitting that a set of operations for water management be formally defined over this new structure.
Extract local flows from different computer surface representation
The local flows are mapped in a structure similar to computer surface representation strucutre
The local flows are mapped to only one structure that will be used to develop the applications
The applications become independent of the original computer surface representation structure
Each LDD grid cell represents a graph node and the flow from a given cell to a neighbor cell defines a graph edge that links these two cells
As TIN local flow has two types of propagation geometry, each type needs a different approach to map TIN local flow to graph.
Each triangle side starting or ending as a local flow represents a graph node. Local flow goes from one side to another side of a triangle, passing through their middle points. The graph nodes identifiers are the same associates to the triangles sides during the triangulation process.
When a local flow goes along a triangle side, the vertices of that side represent graph nodes. The graph node identifier corresponding to triangle vertex is computed adding the total number of triangles sides to the vertex identifier from triangulation.
The local flow goes from each cell to one or more neighbors, passing through their centers. The graph node stores the cell identification number and a graph edge is a link between two cells. Multi flow issue is intrinsic in the contour lines data model. Each cell represents a water flow uniform space.
Each Voronoi polygon is a graph node and each graph edge represents a link between two neighbor polygons. Graph nodes store the Voronoi identification numbers existing in the Voronoi data structure which is similar to the grid cell approach.
DatabaseTerraHydro – Develop environment
TerraHydro is a TerraView plugin, using all TerraView funcionalities
TerraView - GIS application built using the TerraLib GIS library. TerraView main goal is to make available to the GIS Community an easy geographic data viewer with resources that include database queries and data analysis, exemplifying the use of the TerraLib library
LDD Extraction: for each grid cell the local flow is defined considering the steepest downstream regarding the 8 grid cell neighbors. LDD is the basis for developing applications involving water resources.
Upscaling definition:redefinition of local flows in a grid of lower resolution from the local flow extracted from a high resolution grid (LDD)
Accumulation area: each grid cell receives the accumulated value along the paths that is linked with that cell.
Drainage definition:all grid cells subset having accumulated area value greater than that of a user defined threshold.
Tocantis Amazonian River drainage definition example
Tocantins Drainage Zooms
River reaches: define drainage segments, between water springs and junctions, between junctions, or between junctions and mouth of the drainage.
Basin delimitations: the delimitations can be done by selecting one or more points over the drainage. TerraHydro finds the basin for each given point or for each river reach basin.
Red: Basin delimitation
Blue: drianage of main Rivers, extracted from accumulation area
Image size: 1.244.160.000 - Lines: 32.400 Columns: 38.400 - Processing time: 360:16:25 Initial pit number: 65.670.466 - Unsolved pit number: 0
Yellow lines: ArcGis
Red lines: TerraHydro