Final answer:
When the velocity of water decreases, sedimentation occurs and sediment particles settle and deposit on the riverbed or the bottom of a body of water. This can lead to the formation of deltas in rivers with high silt content.
Step-by-step explanation:
When the velocity of water decreases in a river or stream, sedimentation occurs. As the water slows down, the sediment particles have a chance to settle and deposit on the riverbed or the bottom of the body of water.
This is because the slower-moving water has less energy to carry the sediments, causing them to drop out of suspension.
In rivers with high silt content, the slowing water velocity can lead to the formation of deltas at the river's mouth. Deltas are low-elevation areas of sand and mud that form as the silt settles onto the ocean bottom.
On the other hand, rivers with low silt content or in areas with high ocean currents or wave action create estuarine areas where the fresh water and salt water mix.