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Watershed Isochrones
  1. Where was Watershed Isochrones developed?

The software named Watershed Isochrones was developed by undergraduate and postgraduate students and professors from Federal University of Pelotas, who are members of the Research Group on Hydrology and Hydrological Modeling in Watersheds.

  1. Programming language

This software was developed as a script to be used in ArcGIS. Watershed Isochrones was fully implemented in the Python programming language by making use of the arcpy library, which consists of a set of geoprocessing procedures intended for applications in ArcGIS.

  1. Minimum computer configurations

We recommend systems that meet or exceed the following specifications in order to use Watershed Isochrones: 2.2 GHz processor and 2 GB RAM memory. In addition, users also need a licence of ArcGIS 10.1 or higher and the Spatial Analyst extension.

  1. Scope

The objective of Watershed Isochrones is to compute the travel time of flow from each grid cell in the watershed to its outlet and then delineate the isochrones and the corresponding Time-Area Histogram (TAH). Isochrones refer to lines delineated by points of equal travel time to the watershed outlet, whereas TAH corresponds to a graph relating travel time of direct surface runoff from a given point in the watershed to its outlet and percentage of watershed area contributing direct surface runoff to the outlet. The software Watershed Isochrones was developed to execute a set of geoprocessing and hydrology procedures in a logical sequence.

  1. Watershed Isochrones interface and input

Once Watershed Isochrones is installed, it can be accessed within ArcGIS by using its “ArcToolBox”, as illustrated in Figure 1.


Figura 1 – Exemplification of how users can access Watershed Isochrones in ArcGIS.

Figure 1 illustrates information that users have to input into Watershed Isochrones, allowing to note that it is easy to use the tool. This tool only requires the digital elevation model (DEM) and the definition of the watershed outlet, both in format compatible with ArcGIS. For additional information on input, procedures and output, users are encouraged to read the Watershed Isochrones tutorial, which is stored in the same folder where the software is installed.

  1. Results generated by Watershed Isochrones

     After executing various geoprocessing and hydrology operations, Watershed Isochrones generates a map representing the travel time of direct surface runoff from each grid cell to the watershed outlet and another map containing the isochrones delineated in time intervals defined by the user. This tool also provides the corresponding TAH (graphs and spreadsheets), as illustrated in Figure 2.  

figura 2 isocronas

Figure 2 – Digital elevation model (DEM) and outlet imported into Watershed Isochrones as well as some results derived from the tool (maps of travel time and isochrones, and accumulated TAH).