Perform hydrological modeling on massive raster terrain models with SCALGO Hydrology

SCALGO Hydrology

The SCALGO Hydrology software package contains a number of modules for performing basic hydrological modeling on your massive raster terrain models.

The package supports most common raster terrain data formats, including geotiff-, img-, bil- and asc-files. Furthermore, large rasters that are broken up into a mosaic of many smaller tiles can also be read and written effortlessly. The package consists of the following modules, which can be run from a standalone graphical user interface or from a toolbox within ArcGIS.

Flow Directions

Flow directions module example Example of how the flow directions module assigns flow directions to a raster terrain model using the SFD flow-direction model.

Models how water flows on the surface of a terrain. The module computes the flow direction of each cell in a raster terrain model, that is, the directions in which surface water flows from the cell. The directions are assigned to downhill areas of the terrain using one of three user-specified flow-direction models (steepest downslope neighbor (SFD), all downslope neighbors (MFD) or aspect decomposition), and on flat areas using one of two user-specified models (shortest path or geodesic). It is also possible to control how no-data cells are handled.

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Flow Accumulation

Stream Segmentation module example Example of how the Flow Accumulation module assigns flow to each cell of a raster terrain model using the indicated flow directions and an initial flow of one on each cell.

Models how water flows on the surface of a terrain. The module computes the flow accumulation of each cell in a raster terrain model, that is, how much surface water will reach the cell if flow (initial as well as incoming) in a cell is distributed to neighbor cells using its flow direction(s) (computed using the flow directions module). Normally the initial flow on each cell is one, but it can be fully user-specified.

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Stream Segmentation

Stream Segmentation module example Example of how the Stream Segmentation module assigns the same label (color) to cells in the individual segments of streams defined by applying a threshold of 2 to the flow accumulation computed using the indicated flow directions.

Identifies individual stream segments after modeling how water flows on the surface of a terrain. Given SFD flow directions of a raster terrain model (computed using the Flow Directions module) and a threshold, the module computes a stream network by extracting cells with a flow accumulation (computed as in the Flow Accumulation module) above the threshold and then assigns a unique label to stream cells between stream junctions (stream cells receiving flow from several other stream cells).

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Stream Ordering

Stream Ordering module example Stream network with Strahler order numbering of the individual stream segments.

Identifies the Strahler or Shreve stream order of each individual stream segment after modeling how water flows on the surface of a terrain. Given SFD flow directions of a raster terrain model (computed using the Flow Directions module) and a threshold, the module computes a stream network by extracting cells with a flow accumulation (computed as in the Flow Accumulation module) above the threshold and then assigns all cells on a stream segment (cells between stream junctions, that is, stream cells receiving flow from several other stream cells) the Strahler or Shreve order number of the segment.

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Watersheds

Watersheds module example Example of how the watersheds module computes two watersheds (orange and yellow) on a raster terrain model with indicated flow directions.

Computes the watersheds of a terrain model. Given SFD flow directions of a raster terrain model (computed using the Flow Directions module), the module computes for each cell what watershed it is contained in. A watershed is a set of cells where water on the cells flow into the same depression. Optionally, the lowest cell in each watershed can also be computed.

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Adjoint Catchments

Adjoint Catchments module example Example of adjoint catchments.

Constructs a polygon delineating the upstream adjoint catchments of each catchment polygon given as input. The catchments are defined by drainage points and are computed by the Watersheds module. The adjoint catchments of a catchment are simply all catchments draining to that catchment.

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Flooding

Flooding module example Terrain where all depressions (marked in red) have been removed (filled).

Removes (fills) all depressions in a raster terrain model. The depression filling can be viewed as the process of uniformly pouring water on the terrain until a steady-state is reached, that is, depressions are filled exactly so much that there is a path from each cell to the boundary of the terrain through cells with no higher height than the cell itself.

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Sea-Levels

Sea-levels module example The orange terrain indicates the minimal sea-level rise that results in flooding.

Assesses the risk of flooding due to rising sea-level. The module computes a raster model where each cell is assigned a height corresponding to the minimal sea-level rise that results in flooding of the cell (i.e. the level where the cell is connected to the ocean by a path of cells below the level). Normally the sea is defined as all no-data cells, but the module allows detailed control over what is considered sea.

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