requires special care and can involve sophisticated techniques and equipment. 

 Color coding armor units in their initial placement is a simple way of illus- 

 trating the degree of overall displacement of the armor layer. Soundings on a 

 small grid before and after a test will measure the overall volume of material 

 which was moved, though net profile changes can hide more drastic gross move- 

 ments which may have occurred during the test. Photographic or video proce- 

 dures have been used to follow actual movements, including rocking in place, 

 of individual units with good success (Delft Hydraulics Laboratory 1985). 

 Detection of rocking is especially important in testing dolosse or other 

 slender concrete armor units since it is known that they experience signifi- 

 cant breakage in place from impacts between individual units. Testing for 

 damage rates of these units is therefore a highly subjective process because 

 the excessive mechanical strength of model units prevents evaluation of the 

 stability of a design after some of the armor units have broken. Reduced 

 strength model units (Timco 1981) may eventually provide a better means to 

 measure stability of slender units, but model units fully similar to their 

 prototype units in mechanical strength are not currently available. Stresses 

 in prototype concrete armor units are far from fully understood, but research 

 in this area is under way at most leading hydraulic laboratories. 



51. A number of other characteristics are sometimes measured in con- 

 junction with stability tests of breakwater designs, including reserve sta- 

 bility and wave transmission. Reserve stability refers to the extent of dam- 

 age that occurs when the breakwater is subjected to waves in excess of the 

 design condition, an important consideration in risk analyses. Wave trans- 

 mission characteristics require additional tests to be fully defined, par- 

 ticularly when the functional performance design criterion (in terms of wave 

 transmission) is substantially different from the structural integrity design 

 criteria. Runup is a useful parameter to measure in conjunction with wave 

 transmission tests, since the ratio of runup to freeboard seems to be the most 

 sensitive parameter in analytically predicting wave transmission by overtop- 

 ping. Runup is difficult to gage precisely on rough permeable slopes, and 

 traditional visual methods are still common. Measurement of volumetric over- 

 topping rates is also occasionally of interest, but a special setup with pro- 

 visions for containing overtopped water is necessary. Techniques for measur- 

 ing and evaluating the detailed relationship of runup, volumetric overtopping, 

 and transmitted waves to incident waves in terms of wave-by-wave effects and 



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