How to select mainstream from segment lines when having no field can be used?
I have a line layer with segments (one by one connected to each other) of mainstream I would like to keep, but this layer also have some short segment lines isolated from the mainstream which I'd like to delete. These two do not have any field that can divide them.
I want to keep only the mainstream and delete the isolated lines.
1) I have tried "select by location" to select the ones that have 'touching boundary', but some of the isolated lines also kept. They may indicate a big lake, represented by several line segments connected to each other.
2) I also tried "buffer by 1m", then dissolve. But dissolve never worked for me. Please let me know if I need to modify the setting of the dissolve tool.
The streamline I wanted is supposed for one basin, so any line segment is connected to any other segment.
The off-stream lines I want to delete may have several segment connected, but have not connection to the mainstream system.