Correct option is A
Silting:
It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary or permanent) of fine sediments on bottoms where they are undesirable.
Siltation or the deposit of silt in waterways can be caused by soil erosion from water and land activity.
The main way to avoid this type of pollution in water is avoiding soil erosion in the first place, this can be done by monitoring or lessening activity in these areas that lead to soil erosion.
Defective outlet and head regulator, along with inadequate slope and not-regime section result in silting of the channel.
Scouring:
Due to high flow velocity the bed material of unlined canal washed away, this phenomenon is called scouring of canal bed.
Scouring lowers, the full supply level and causes loss of command.
It may also cause breaching of canal banks and failure of foundations of irrigation structures.
If water of a given velocity and depth is not fully charged with silt (that it can carry in suspension) it will scour the bed and sides of the channel, till it is fully charged with silt.
Hence, if the velocity of flow in the channel is more, the bed and the banks are likely to be eroded, and similarly, if the velocity is less, the silt which was formerly carried in suspension is likely to be dropped.
