When there is too much water.
S1 When there is too much water in a place.
S2 Yes, when there is too much water in rivers or in the sea.
S1 And it can't stay in its place.
S2 Yes, and it comes out of the rivers or the sea.
S1 And it covers big areas of land.
S2 Yes, and it destroys things and makes a lot of damage.
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and negotiation of meaning