Question

how is sand that flow in a river formed?collect some imformation about whesethe sand comes from:

Answer 1

the sand in rivers are actually rocks which flowed in the river and hit others rocks.because of the flow of water and hitting of rocks the rocks broke down in small pieces.this process continued to form the sand in rivers

Answer 2

Whenever the river erodes, it erodes the rocks from the higher grounds. The river has immense energy to erode a bigger boulder. It erodes the bigger one and make it small, like pebble stones.  

Further the river erode the pebbles to form sand and clay.

Most of the rocks and pebbles travels along with the water course where sand and clay travels along with the water columns in a creamy form.

When the river loss its energy during the dry season the sand and clay gets sediment to the bottom on the river.