Hidrografia (2/5): direção de fluxo (flow direction) e definição de cursos d'água (streams) no QGis

Summary

This instructional video guides viewers through the process of delineating a sub-basin of the Canoas River in Urubici using GIS tools. The speaker demonstrates how to use the 'R watershed' tool to fill depressions in the digital elevation model and select key parameters for accurate hydrographic mapping. The video emphasizes the importance of careful parameter selection and file management to generate accurate water flow and drainage direction maps, leading to the identification of critical sub-basin areas for further hydrological analysis.

Takeaways

• 😀 The process involves delineating a sub-basin of the Canoas River in Urubici using GIS tools.
• 😀 The initial step involves using tools to fill depressions and ensure the model is accurate before starting the analysis.
• 😀 The R Watershed tool is used to generate necessary outputs for the watershed analysis, such as stream channels and flow direction.
• 😀 Setting the minimum basin size is crucial for the analysis. In this case, a value of 500 was chosen based on previous tests.
• 😀 Some unwanted output layers like topographic index or firepower index can be deselected to streamline the process.
• 😀 It's important to save all generated files to avoid losing progress if the software or computer closes unexpectedly.
• 😀 The user is advised to exercise patience as the tool may appear unresponsive during processing but continues to work in the background.
• 😀 Two main output files are generated: a raster layer for stream channels and a flow direction layer for drainage patterns.
• 😀 The identification of the basin outlet (where the basin drains) is a critical step for the analysis, marked by a specific pixel.
• 😀 Output files should be renamed (e.g., 'Canais' for stream channels) and stored in a dedicated folder for easy access.

Q & A

What is the main task described in the video script?

The main task in the script is to process and delimit a hydrographic basin, specifically a sub-basin of the Canoas River in the municipality of Urubici.

What was done in the previous video lesson that is relevant to the current task?

In the previous lesson, new layers were created for a specific area around Urubici, and a tool was used to fill empty spaces or spurious depressions in the region.

Why is it important to perform the initial steps of delimiting the basin?

The initial steps are crucial for ensuring that the subsequent processing can be done correctly. It helps in refining the area before applying tools for further analysis.

Which tool is used in this script for processing the hydrographic basin?

The tool used in this script is the 'R Watershed' tool, which is part of a set of tools in the 'GAS' group.

What is the significance of setting a minimum exterior size for the basin?

The minimum exterior size of 500 is chosen to control the level of detail in the output. A smaller value provides more detail, while a larger value simplifies the results.

What output does the 'R Watershed' tool generate?

The 'R Watershed' tool generates two main outputs: a raster layer of flow direction and a layer of watercourses (streams) within the basin area.

What does the 'Flow Direction' output represent?

The 'Flow Direction' output represents the direction of water flow across the terrain, which is critical for understanding drainage patterns in the basin.

What is the importance of the final blue pixel mentioned in the script?

The final blue pixel marks the outlet of the basin, which is essential for identifying the exit point where the water leaves the sub-basin.

Why is it important to rename the files generated during processing?

Renaming the files ensures better organization and prevents losing important information, especially since the files are temporary and could be lost if not properly saved.

What should be done after generating the layers and files in the script?

After generating the layers and files, it's important to save them in a dedicated folder to avoid losing data, as these files are temporary and will be lost if the software or machine is closed.