Ch. 22] 



SUSPENDED-SEDIMENT LOAD 



391 



SEDIMENT 



CONCENTRATION 



IN WATER 



SEDIMENTATION OF IMPROVED 

 CHANNELS. FLOODWAYS, 

 DITCHES, AND CANALS 



SEDIMENTATION 



RESERVOIRS 



DEPOSITION ON 



LAND. IMPROVEMENTS 



AND HABITATS 



CHANNEL AND VALLEY AGGRADATION 

 RESULTING IN INCREASED FLOOD STAGE 



Fig. 9. Effects of sedimentation. 



found that on an average, in the piedmont section of North Carolina, 

 an increase of turbidity from 100 to 1,000 parts per million required a 

 70 percent increase in the quantity of alum used to flocculate the sedi- 

 ment. Higher turbidity also necessitated more frequent cleaning of 

 settling basins and increased certain other costs. Most of the sedi- 

 ment that is filtered from surface water is fine-textured, ranging from 

 silt to colloids, and in most streams it comes mainly from widely dis- 

 seminated sheet erosion (Garin and Gabbard, 1941). Except where 

 water-intake characteristics or plant facilities could be improved, re- 

 duction in the costs of water treatment can be accomplished only by 

 widespread control of soil erosion on the watershed. 



Fine suspended sediment seriously impairs the value of streams and 

 lakes for recreational use. It reduces the population of game fish and 

 lessens the desirability of water for swimming (Brown, 1945a). It 

 also causes heavy losses of commercial-fish and shellfish yield from 

 both inland and tidal waters (U. S. Congress, 1946). With few ex- 



