Distribution Graphs of Suspended-Matter Concentration

Damages or benefits resulting from sedimentation at various points in a drainage basin may be due to different types of sediment, possibly coming from different sources. For instance, flood and drainage damage caused by stream-channel aggradation appears to be primarily a bed-load problem, involving the deposition of relatively coarse material. On the other hand, fine material is responsible for much of the deposition in irrigation and drainage canals and the increased cost of water purification in many public water-supply systems. Both fine and coarse material contribute to the deposits in reservoirs, but the finer grade of sediment normally is the chief source of damage, because it constitutes the greater portion of the load. Because different types of damage are caused' in different proportions by the two classes of sediment, it is important in sediment-load investigations that, not only the total load of the stream be determined, but also the relative proportions of fine and coarse material. These are the subjects discussed in the paper.