open TELEMAC-MASCARET The mathematically superior suite of solvers

I am not totally sure which one is the island you are talking about, but I assume it is the coastline in the bottom of the picture.
As you might see, the mesh has many points (nodes) to attach along the coastline, but your outline (the long bow) has very few points where the mesh can attach.
Try to spread the nodes along the bow in a even distance. Choose the distance depending on the detail you need along the bow and then try to create a new mesh.
Try also to create a mesh with the option "Resample Outline" turned off and see how this looks like.

Hope that helps

yes i had resampled and when i maked island as softline and not hardline, the mesh was done.
But the islands were deformed.

That the islands gets deformed when you make them as softlines is normal, but since they are islands you should insert them as hardlines.
To get a better mesh you need to spend some time refining you lines in QGIS. Here some simple steps.

1. Create points in a even distance along the coastline. The distance defines the detail of you mesh along the coastline. Let's say 10m should be fine.
2. Connect the points with a line. Then you have you coastline.
3. Do the same with the Island, but create a closed line for each island.

4. I assume you do not need that much detail in the north of the model (the bow). Create here as well points in a even distance but maybe just 100m or 200m.
5. Connect the points along the line
6. Merge the coastline and the line along the bow.

Now you should have the outline (bow+coastline) and a closed line for each island.

7. Import the outline to BK and set it as outline for your mesh
8. Import the islands to BK and set them as hard lines.

9. Create the mesh with the option "Resample Outline" turned off and set the edge length do the distance of you point distance along the bow.

If you need areas with more detail use the options BK provided for that.

Good luck

Okay, I will follow your message step by step.
I hope that I will succeed in generating this mesh.

Thank you so much for your help.
YASMINA