Delineating watershed using QGIS

 

3.1             QSWAT

Install QSWAt and launch it from plug in

Click on new Project after saving,  select delineate watershed from the new popup window

This will ask you to select a DEM 

Now determine the sub watershed size either by setting the the number of pixels or the area in hectare or sq km

After determining the size click on create streams

the streams created and appear in the canvases as follow

Add your outlet (The red one) what you want to delineate / a point obtained from field

Select draw inlet/outlet

the cursor will be ready to add a point to your watershed delineation database. 

 and click on a stream which is closer to your outlet. this will make a point with blue triangle symbol as an outlet for the watershed delineation 

Then click ok 

Click on “select  inlet/outlet” and select the outlay you draw in the previous step you can select many outlets by using shift key

Click exactly on the out let (with blue color) created  to be sure the color will be changed to yellow to indicate he outlet is selected 

after selecting the outlet, click on save then it says one feature select

Finally click on create a watershed icon

the watershed with its sub micro watershed will be produced!

In order to avoid micro watersheds

•        Open attribute Table è Select All

•        Save the dialogue box

•        Merge