And when, exactly, are we playing Churchill again?
If you mean after "waters rise" you draw a card for a tile that is already flooded, can you play sandbags to save the tile from sinking - the answer is no. A flooded tile is sunk immediately when you turn over its card. There is no time to play the sandbag before the tile sinks.
Just to clarify for the OP: you draw a Waters Rise card. EEEK! I could lose one of these flooded tiles! NOW is the time for you to play the sandbag card, not after you've seen what tiles are actually going to be flooded.