Why does the Hjulstrom curve have its shape

As grains get larger, they require more energy from the transport medium to erode away.Larger grains are deposited at higher energies than smaller grains because they require an even greater amount of energy to move.The very left hand side is explained by the platy and cohesive (means they can stick together) nature of clay and silt particles, this means more energy is required to move them, but when they are moving, they will stay in the suspension for longer as they are so light.