The factors affecting Manning's roughness coefficient are cross sectional geometry and boundary roughness surface roughness, vegetation on channel , channel irregularity , channel alignment, silting and scouring, obstruction, size and shape of channel, stage and discharge, seasonal change, and suspended material .The value of Manning's n is affected by many variables. Factors like suspended load, sediment grain size, presence of bedrock or boulders in the stream channel, variations in channel width and depth, and overall sinuosity of the stream channel can all affect Manning's n value.