Chaptek 19 

 DEBRIS CONTROL 

 Burnham H. Dodge 



Chief. Hydrology and Flood Operations Section 



Los Angeles District, Corps of Engineers 



Department of the Army 



Los Angeles, California 



THE PROBLEM 



The control of debris is a specialized consideration in the field of 

 sedimentation. In this sense, the term debris has come to mean sedi- 

 ment particles usually ranging in size from fine sand to the largest of 

 boulders (see Fig. 1). The term is also associated with the movement 

 or deposit of such material in considerable quantity. Extensive debris 

 deposits, called debris cones and alluvial fans, are well-known and 

 easily recognizable geological features found at the mouths of steep 

 canyon drainage areas. The conditions and processes that lead to 

 formation of debris cones are beyond the scope of this discussion but 

 may be found in most standard textbooks on geology. 



Debris becomes a problem and requires control when man's develop- 

 ment and use of land encroach on the area where flood flows carry and 

 deposit debris. Many existing problems of this nature would have 

 been avoided if original settlers had recognized such areas and been 

 aware of the attendant erosion processes. 



Debris-producing areas exist in many places throughout the world. 

 The three areas mentioned below, all in the western United States, are 

 those for which detailed information is readily available and in which 

 different methods of control have been practiced. 



In southern California, debris-cone areas are common along the 

 west face of the coastal ranges. Of particular concern is the area 

 along the base of the San Gabriel Mountains, within Los Angeles 

 County. These mountains rise about 3,000 feet and more in a space 

 of 1 to 3 miles. They are rugged in character, drained by precipitous 

 canyons, and have a surface of shattered, deeply weathered rock cov- 



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