I have found the following meaning for  the word "storyline" in the monolingual dictionary [LONGMAN, Dictionary of Contemporary English, Longman, 2003, p.1637]:

STORYLINE:  also STO-RY-LINE / n [C] the main set of related events in a story; = plot: the play had a strong story line.

I have not found any meaning of the word "storyboard" in the monolingual dictionary.

Moreover I have found the following meaning of the word "storyline" in the net
[webliography: www.wordreference.com]:

STORYLINE: noun; plot line (the plot of a book or play or film).

I have not found any meaning of the word "storyboard" in the net.