Need help with these two questions!

1. A dredger ship floats in a canal section which is isolated by lock gates. Explain what happens to the water level in the canal when the dredger lifts up, and takes on board, silt from the canal bed.

2. On some clear winter nights, the windscreen and rear window of my hatch-back car,which is parked in the street, get covered with frost, but the side windows do not. Why is that?