Hey there! I'm happy to help!
The topography of the Earth is all of the unique changes in landscape with the different formations, elevation changes, etc.
It appears that this question is talking about rivers because it mentions something that carries huge amounts of water. Rivers are a principal factor in the sculpting of the Earth's surface as water can erode rocks and transport the sediments to other locations.
Rivers take water and transport to the sea. The sea is basically the ending point of the rivers as there is no where else for it to go. It is at the lowest elevation, so the rivers can't really flow anywhere else now.
Have a wonderful day and keep on learning! :D