Answer:
The correct answer is High Basin, where the Headwater stream or source is located.
Explanation:
Rivers help the soil to become fertile by depositing Sediments, nutrients and organic material that is carried down with the stream in them.
Rivers are divided into High, medium and low Basins, High meaning the source of the river location, and low is where the mouth is located. The part of the river where there are lower sediments is in the High Basin where the Headwater Stream (or Source) is located, the reason behind this is that Sediments and nutrients are dragged by the river along their course until they reach the mouth of the river and in the Source the river hasn't dragged any sediments nor nutrients yet so the soils are not as fertile.
