Here's why:

* Moving water carries sediment: Water, especially moving water like rivers or ocean currents, has energy. This energy allows it to pick up and carry sediments like sand, silt, and rocks.

* Energy loss leads to deposition: As water slows down, its energy decreases. This can happen due to various factors:

* Change in slope: A river flowing down a steep slope loses energy as it enters a flatter area.

* Entering a wider channel: A river spreading out into a wider area slows down.

* Reaching a still body of water: A river entering a lake or the ocean slows down significantly.

* Sediment settling: When water loses enough energy, it can no longer carry the sediments it was transporting. The sediments then settle out at the bottom, forming deposits.

So, the loss of energy is the key factor driving sediment deposition.