Lacy’s regime condition is obtained if A. Silt grade in the channel is variable B. Discharge in the channel is variable C. Silt charge in the channel is variable D. Channel flows in unlimited, incoherent alluvium of the same character as that transported material

The correct answer is D. Channel flows in unlimited, incoherent alluvium of the same character as that transported material.

Lacy’s regime condition is a state of equilibrium in which the channel slope, sediment load, and channel geometry are all in balance. This condition is only possible if the channel flows in unlimited, incoherent alluvium of the same character as that transported material.

If the silt grade in the channel is variable, the channel will not be in equilibrium because the sediment load will be constantly changing. If the discharge in the channel is variable, the channel will not be in equilibrium because the water flow will be constantly changing. If the silt charge in the channel is variable, the channel will not be in equilibrium because the amount of sediment deposited in the channel will be constantly changing.

Only if the channel flows in unlimited, incoherent alluvium of the same character as that transported material will the channel be in equilibrium. In this condition, the sediment load will be constant, the water flow will be constant, and the amount of sediment deposited in the channel will be constant. This will allow the channel to reach a state of equilibrium in which the channel slope, sediment load, and channel geometry are all in balance.