The word volcarás is the future form of volcar in the second person singular. There are other translations for this conjugation.
See the full volcar conjugation

volcar

Dicen que el peso del agua es tan grande, que en una curva, el agua se ira a un lado y volcaras.
One thing they said is that the weight of the water is so immense, that as you go round a corner, you could slosh over to one side and roll over.
La volcarás sobre ella.
You spill it on her.
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