78. Character of Materials in the Littoral Zone. - The beach, the 

 nearshore and in some cases the offshore area to considerable depth is 

 included in this general category. Samples of surface material in the 

 littoral zone must be obtained in order to define its composition. 

 Customary procedure is to obtain samples of the top 2 inches of material 

 at the mean water line and along the profile at 5-foot depth intervals 

 seaward as far as a regular sorting pattern along the profile is indicated. 

 Any sampling device that will secure a representative sample without loss 

 of fines is suitable. ^ For sandy material, -g-pint to 1-pint samples are 

 usually adequate. Spacing of sampling profiles depends upon regularity 

 of the shore and slopes, and on long straight beaches profiles quite 

 widely spaced will usually provide adequate definition of the areal 

 distribution of materials in the littoral zone. 



79 « Since the size distribution is of primary concern, all samples 

 are subjected to mechanical analysis. Sieving or settling velocity methods 

 are equally acceptable for this purpose. Uniform size classifications 

 (based on Casagrande classification) approved by the Corps of Engineers, 

 January 19^2 are given in the following table. 



Table 7 - Standard Size Classifications- "- 



Name Grain size limits (diameters) 



Boulders Above 12 inches (305 millimeters) 



Gobbles 3 inches to 12 inches (76 mm to 305 mm) 



Coarse gravel 3/^ inch to 3 inches (l9 mm to 76 mm) 



Fine gravel -;Hf No, h sieve to ^ inch (U.7 mm to ].9 mm) 



Coarse sand No. 10 sieve to No. k sieve (l.9 mm to U,7 mm) 



Medium sand No. UO sieve to ^^o. 10 sieve (0,I|.2 ram to 1.9 mm) 



Fine sand No. 200 sieve to No. kO sieve (0.07ianm to 0,lj.2 mm) 



Silt or clay Passing No. 200 sieve (O.OOl mm to 0,07ll- mm) 



* Corps of Engineers Uniform Soil Classification 

 -x-» U. S, standard sieve size 



80, Preparatory to mechanical analysis^ the samples a re w sshed free 

 of salt, dried, and quartered down to about $0 grams. They are then 

 sieved or placed in settling velocity tubes and cumulative gradation 

 curves are constructed. From these curves the grain size at the first 

 and third quartiles and the median are read. Three general comparisons 

 are ordinarily made, (l) the median diameter, (2) the sorting factor, 

 and (3) the skewnesso The sorting factor is defined as V Q1/Q3 • The 

 skewness is (Qi x Q^)/U^ where Q]_ and Q3 are the grain size at the 25 

 and 75 percent finer points, respectively, and M is the mean diameter, 

 all 'in millimeters. Beach studies have indicated (Schalk, 19U6) that as 

 the grain size increases or decreases with seasonal changes at one 

 location on the beach, the grain size at other locations show a correspond- 

 ing increase or decrease. As the littoral zone sorting is very good on 

 most shores the median diameter is generally an acceptable parameter. 



56 



