What is the slowest stream velocity necessary for a stream to carry the smallest boulders?

The slowest stream velocity necessary for a stream to carry the smallest boulders typically ranges between 1.5 to 2.5 meters per second (about 5 to 8 feet per second). This velocity allows the water to generate sufficient lift and transport capacity to overcome the weight of the boulders. Variability in streambed material, boulder shape, and water density can affect the exact velocity required.