The main ways sediment enters a river are mass movement and

Runoff

Explanation:

The sediments enters the river through the process of mass wasting and runoff. The mass wasting is a process of downward movement of the materials such as soil, stones, pebbles and others down the slope. This may occur because of landslides and mudslides. In such situations the materials become unstable due to the effect of gravity they fall of.

The runoff is the process of flow of sediments and materials along the flow of water. These sediments and materials will become the part of river when the water from river streams, lakes, ponds, rainfall and glacier melting enters the river.