No, Joel is not right. The sand lies still, so nothing is carrying it now.

Up on the hill, the river ran fast, and fast water carried the sand along.

At the lake, the river slowed down. Slow water cannot hold the sand up.

So the river dropped the sand, right where it slowed down.

The river reaches the lake, and slows down. It drops its sand in a flat fan.

When small pieces settle to the bottom of water, we call them sediment.

Grain by grain, the sand settled and built the flat fan.

A river flowing into a lake, with a fan of sand at its mouth.