The river runs however long, all the while picking up sediment, sand, rocks, etc. and continue doing this for the river's length, and at the very end of the river (mouth), all of this sediment is deposited, leaivng sand at the river mouth.
I have several sentences for you.The mouth of the river is wider than the rest of the river is.The water at the mouth of the river was filled with silt and sand.There were many sand bars at the mouth of the river.
The soil deposited at the mouth of a river is called silt.
That is called a river 'delta'.
a river delta for HI2 "delta"
Delta
sediment
Delta
A Delta is formed
Delta
Erosion of the river banks altering the course; deposition of gravel, sand and mud in calmer stretches; obstructing of the river mouth with sand-bars forming in the estuary and inshore.
The abrasion and attrition combined with hydraulic action on the river bed and the river banks erode away the underlying rock which results in small grains of rock we call sand. Depending on the speed of the river and the size of the particles, the sand will be deposited by the river at different stages (usually though it is found near the mouth of the river).
an alluvial fan