In this NHK News Easy story, the second paragraph describes an online video showing a river suddenly flooding.
The tense is constantly changing in this paragraph and I'm not sure why. Oddly enough, it seems to change from present tense at the chronological BEGINNING of the narrative, to past tense at the chronological END.
初めは、水は静かに流れています。At first, the water is quietly flowing (present tense). そこに、急に水がたくさん流れてきます。Then, the water will be flowing a lot (~てきます is future tense, according to this). 川はすぐに茶色の水でいっぱいになりました。The river immediately became full of brown water (past tense). 流れる水の力もとても強くなりました。The force of the flowing water also became much stronger (past tense).
Am I interpreting these sentences correctly? How should I interpret the changes in tense?
そこに question: The second sentence uses そこに like a conjunction, but I can't find any entry for this そこに in dictionaries; only そこで. Is this そこに to be interpreted as a conjunction, or literally as そこ ("there") + に ("at / in")? If the latter, what purpose does it serve by being included here?