QGIS Watershed Delineation for Beginners | Simple & Clear Guide (2025)

Welcome, In this tutorial, you'll learn how to perform watershed delineation using QGIS – a powerful open-source GIS software. Whether you're a beginner or need a refresher, this guide walks you through the entire hydrological analysis workflow using tools like SAGA and GRASS GIS within QGIS.
Topic Covered:
1.Tutorials for Downloading DEM data
2.Reprojecting Data: Geographic to Projected Coordinate System (GCS to PCS)
3.Understanding and Using the Fill Tool in QGIS
4.Introduction to Strahler Stream Order and Its Application
5.Setting Stream Order Threshold Using the Raster Calculator
6.Stream Network Reclassification Based on Order
7.Converting Raster Stream Network to Shapefile
8.Performing Watershed Delineation in QGIS
9.Exporting Watersheds to Shapefile Format
10.Clipping Stream Network Using Watershed Boundaries
11.Visualizing and Styling Final Results for Presentation
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Important Links:
1. Playlist for Downloading DEM data:
   • Downloading DEM (Digital Elevation Model) ...  
2. Find UTM Zones for your Region:
UTM Zones: https://www.dmap.co.uk/utmworld.htm
3. Fill Tool Link:
https://pro.arcgis.com/en/pro-app/lat...
https://saga-gis.sourceforge.io/saga_...
https://www.researchgate.net/figure/W...
4. Strahler's Stream Order:
https://earthhow.com/stream-ordering-...
https://water.dpie.nsw.gov.au/about-u...
5. Deterministic (D8) Flow Direction (Upslope Area)
https://www.researchgate.net/figure/T...
Flow Direction (Number and its Direction)
-1,2, 4, 8, 16, 32, 64, 128, which indicates 8 directions, that is, east, southeast, south, southwest, west, northwest, north, and northeast. (https://help.supermap.com/iDesktop/en...)
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Geographic Coordinate System vs Projected Coordinate System
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Feature Geographic (GCS) Projected (PCS)
Units: Degrees Meters, feet, etc.
Shape: Curved (spherical) Flat (2D)
Good for: Global datasets, GPS Local/regional accuracy
Spatial analysis
accuracy: Low High
Distance/
area calculations: Distorted Accurate
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00:00 Introduction
00:10 Adding DEM data
00:34 Tutorials for Downloading DEM data
00:56 Examine DEM data & its Properties
03:10 Reproject DEM data (GCS to PCS)
05:18 How to Find Projected Coordinate System (PCS) for your Region
09:28 Adding Basemap
10:15 Clipping DEM data
12:51 What is Fill Sink & How to Use
17:28 Strahler Order (Introduction & How to Use)
23:43 Raster Calculator (Setting Threshold for Strahler Stream Order)
25:30 Classifying Strahler Stream Order
26:33 Converting Streams into shapefile format
26:56 Watershed Delineation / Upslope Area
34:18 What is Deterministic D8 Method?
37:19 Converting Watershed into Shapefile format
38:12 Clipping Stream with Watershed Boundary
39:57 Visualizing and Styling Final Results
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