(e) Wave attenuation hy the breakwaters as wave conditions 

 and structure configurations were changed. 



Four different tests were conducted in two general fields of emphasis-- 

 properties of the nylon bag and performance of the bag breakwater structure. 

 The nylon sandbags were tested to determine damage from exposure to sun- 

 light, behavior when dropped through water, and weight changes from air 

 retention while submerged. The original plans for the bag breakwater tests 

 specified 13 different combinations of structure height and crest width; 

 however, because of restrictions on scheduling the use of laboratory facil- 

 ities, only four structures [three submerged and one emergent) were tested. 

 The laboratory construction method was similar to that used in the field; 

 i.e., bags dropped into position through water. The four structures were 

 tested to determine wave attenuation and breakwater configuration changes 

 while under wave attack. No tests were performed in which the constructed 

 crest width was deliberately varied while the structure height was held 

 constant; therefore, the investigation of the dependence of wave attenua- 

 tion and bag stability on structure configuration was severely limited. 



'II. BAG PROPERTY TESTS 



1. Exposure Test . 



Uncoated or unprotected white nylon deteriorates under exposure to 

 sunlight, specifically ultraviolet light. By the spring of 1967, several 

 field installations of protective revetments had been built of bags and 

 subjected to exposure damage. An estimate of the lifespan of nylon sand- 

 bags exposed to the weather (protected from vandalism and wave action) was 

 needed for comparison with the performance of alternate construction mate- 

 rials. A single bag was filled with sand and left on a sandpile exposed 

 to the weather from April 1967 to September 1968 (Fig. 1). Periodically, 

 the bag was probed with the toe of a shoe to test the condition of the 

 material. Between October 1967 and the end of the test, the bag split 

 open along the length of the upper face, evidently due to photochemical 

 (actinic) deterioration of the nylon filaments (Fig. 2). 



2. Drop Test . 



Before beginning the breakwater tests, the CERC investigators needed 

 to know if bags dropped into water would land in a stable position. Four 

 bags filled with dry sand to about 75 percent capacity were dropped into 

 10 feet (3.05 meters) of water, inspected, and photographed by divers. 

 Each bag landed flat on the bottom and retained a trapped air pocket that 

 slowly leaked. Bags were also observed to land flat on the bottom or on 

 top of other bags during the subsequent breakwater tests, but those with 

 wet nylon material retained large air pockets when placed either below 

 or above the Stillwater level. Since nylon filament swells when wet, the 

 swelling was assumed to be the cause of permeability loss. 



iO 



