presents a graph to use as a guide in selecting riprap size (Figure C-2). 



ai 

 z 

 o 



&5 



CO 



z 

 < 



CO 



< 



o 

 o 



— 6' 



100 300 500 700 900 1100 



EQUIVALANT SPHERICAL DIAMETER OF 

 STONE I mm) 



CURVE 



SPECIFIED 

 STONE SIZE 

 %PINER 



D33 



^50 

 D40 

 D65 



Ocallf.Hgws. 



©Bur Public Rds 



©Bur of Reclamn. 



©Corps of Engrs 



© Recommended Curve D50 

 fo' a Guide (Neill, 1973) 



Assumed stone specific gravity = 2.65 



BANK SLOPE 



2 1 



2.1 



not given 

 not given 

 horizontal to 2 1 



Figure C-2. Graph of riprap size vs. local flow velocity 

 (modified from Neill 1973). 



It should be used with caution because not all aspects are incorporated. 

 Well-graded material improves the interlocking of the rock and reduces spaces 

 between rocks. A recommended gradation is shown in Figure C-3. 



Density and Durability . The rock used for riprap should be hard, dense, 

 and durable to withstand cycles of wetting and drying, and freezing and 

 thawing. These cycles can cause cracking of the rock, resulting in reduction 

 of size and erosion resistance. Density and durability are generally deter- 

 mined by laboratory tests. 



120 



