Your text as it should read: "One stormy day, it just came to life from hills attacking the roads. Since its flowing waters could not be stopped, people suffered, although no one was hurt."
Comment: Do not use a semi-colon after roads as one responder said. Use a period. Why? Semi-colons are used when the text of each part uses a similar construction syntactically. As in,
"One stormy day, it just came to life from hills attacking the roads; floods cascading through like ammunition; and rubble bowling with the peoples' houses as if they were pins."
Each piece of text is balanced in its structure.
In your essay, "roads" is followed by a subordinate clause of the main thought "people suffered". It has a different structure from the previous thought , which is the object of the preposition "from" (i.e. From what?...From hills...) followed by a participle phrase "attacking the roads". To connect these two very different structures would be unbalanced, awkward rhythmically and not good English.
Also, put a comma after "suffered" as it is followed by an independent clause. I would probably use brackets instead of a comma, as it is an aside thought.
Change the verb from "cannot be stopped" (present) to "could not"--past conditional-- to agree with time sense as in "came" (past)
2nd paragraph, 2nd line: use a period (.) after "ours" It is the end of a complete thought. "however" starts a new thought so should be capitalized.