During low flows,
a stream's natural assimilative capacity is greatly reduced, amplifying the negative impacts of natural and human-induced waste loads During high flows, the major concerns are inundation, erosion, and sedimentation.
Flow variation impacts on water resources can be expressed in terms of the change in velocity of flow (ft/s) and rate of discharge (ft/s).
Transportation activities such as earthwork (cutting or filling), site clearance, paving, bridge and culvert construction, ditch and drain construction, and turnout construction often result in rearrangement of ground surface and topography, and therefore alter stream flow patterns, causing too little water availability in certain areas and too much in other areas.