This ILWIS User’s Guide has been rewritten and extended by Raymond Nijmeijer Figure The process of tunneling using two different tunnel widths. Today I’ll start with a new series of tutorials for an open Source GIS called “ILWIS GIS“. ILWIS is the short term for “Integrated Land and Water. A complete package: ○ image processing. ○ spatial analysis. ○ digital mapping . ○ Easy to learn and use: ○ full on-line help. ○ extensive tutorials for direct.

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The objective of this tutorial is to provide users with a better understanding of how the hydrological analyses within ILWIS works, in addition to providing the instructions necessary to reach the desired output for their study region.

It is an open source Geographic Information System software program that was designed to be a user-friendly integrated software that contains both raster and vector processing capabilities, allowing for both analyses on remotely sensed images, vector maps and numerous spatial modeling abilities.

This tutorial will focus on its ability to use Digital Elevation Models DEMs to run hydrological analyses of a ilwls region. This project will focus on hydrological analysis of Okanagan Lake, a popular tourist destination in British Columbia, Canada.

In order to carry out this exercise, a DEM of the area of interest is needed. This can be downloaded from the QGIS website. Before starting any analysis, create your working folder and ensure all data needed for the exercise are in this folder. Keeping all your data in one folder will make analysis easier. In the future, newer versions may also be 33.8, but the tutorial will need to be verified on them.

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Exploring Hydrological Analyses using ILWIS

You will have to navigate to the working folder and select the DEM. Under Save as browse to the desired folder location for your projected DEM and rename it. Fills should be run on DEMs to remove any local depressions, which can cause inaccuracies in following hydrological analyses. Flow direction depicts a main direction of flow run-off.

The flow direction operation determines into which neighbouring pixel any water from a given pixel would flow. This is determined by a moving 3×3 window for every single pixel, based on its neighbouring pixels height values.

Digital Geography

Flow Accumulation performs a cumulative count of the number ilwls pixels that would flow into any given cell on the way to an outlet. This operation is commonly used to determine potential drainage patterns of terrain.

Flow Accumulation is calculated from the map created in Flow Direction, counting the number of cells that tuotrial drain into outlets based on the flow direciton. Drainage Network Extraction extracts a drainage network map.

The map is boolean and will illustrate the drainage as pixels with value True, while all other pixels have value of False. The pixel value is determined by the Flow Accumulation Map and a threshold value. The threshold value in this operation is the minimum value required for ilis flow to be considered True in a drainage network, all cells with a value lower than the threshold will be classified as False. More information on the operation can be found at the Drainage Network Extraction webpage.

Drainage Network Ordering operation finds all drainage line in the Drainage Network and their nodes, and applies a unique ID to each stream. More information on the operation can be found at the Drainage Network Ordering webpage.


Output consists of both a map and a Table. The table lists all the streams with ID values, coordinates, lengths, slope of drainage.

Exploring Hydrological Analyses using ILWIS – CUOSG

This can be seen in Figure Overland Flow Length overland distance towards the ‘nearest’ drainage for each pixel based on flow paths available from the Flow Direction Map.

This will create a map showing the distance a flow must travel to reach the outlet of a given watershed. The output map will show the different sub watershed and the flow length for each cell to reach the outlet. To determine the flow length of a specific cell, use the normal mouse cursor and click on the area of interest. The flow length value in metres will appear in the table on the bottom left portion of the screen.

This tutorial covers the most basic hydrological tools for a more simple and basic hydrological analysis using ILWIS. Operations that have not been covered but should be considered when desiring a more in-depth and accurate analysis include:. For a more in-depth analysis look into the topics not covered in this tutorial.

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