62 



transparent. The use of GPR in marine environments is limited because salt 

 water is non-transparent to electromagnetic radiation in the radio frequencies. 



Morphologic and Bathymetric Profiles 



Periodic topographic and nearshore bathymetric surveys constitute the most 

 direct and accurate means of assessing geologic and geomorphic changes over 

 modern time scales. Time series data, such as repeated beach profiles, allow 

 the assessment of erosion and accretion in the littoral zone. The preferred 

 surveying technique involves collecting a series of shore-normal profile lines. 

 These must extend landward of the zone that can be inundated by storms, 

 usually behind the frontal dunes. 



Permanent or semi-permanent benchmarks are required for reoccupying 

 profile sites over successive months or years. On rapidly transgressing coasts, 

 these benchmarks should be located at the landward end of the profile line in 

 order to minimize their likelihood of being damaged in storms. The locations 

 of survey monuments must be carefully documented and referenced to other 

 survey markers or control points. The ability to accurately reestablish a 

 survey monument is very important because it ensures that profile data col- 

 lected over many years will be comparable (Hemsley 1981). Locations that 

 might experience dune burial should be avoided, and care should also be taken 

 to reduce the visibility of benchmarks to minimize damage by vandals. 



Both the frequency of the sampling and the overall duration of the study 

 must be considered when planning a beach profiling study. Morphologic 

 changes of beaches can occur over varying time scales, and if long-term 

 studies are to be conducted, the dynamic nature of the beach should be taken 

 into account. Often, it is financially or logistically impractical to conduct 

 frequent, repeated surveys for a sufficient length of time to obtain reliable and 

 comprehensive information on long-term processes at the study area. 

 Nonetheless, resurveying of profile lines over a period of more than one year 

 can be of substantial help in understanding the prevailing seasonal changes. 

 Resurveying of control profile lines at selected time intervals can reveal sea- 

 sonal patterns. In addition, special surveys can be made after significant 

 storms and events to determine their effects and measure the rate of recovery 

 of the local beach system. At a minimum, summer and winter profiles are 

 recommended. Unfortunately, there are no definitive guidelines for the timing 

 and spacing of profile lines. Table 8 outlines a suggested survey schedule for 

 monitoring beach fill projects. In summary, observation over a period of time 

 is recommended in order to document the range of variability of morphology 

 and bathymetry. 



Some issues concerning the spatial aspects of study include the spacing of 

 profiles, longshore dimensions, and cross-shore dimensions. Profile lines 

 should be spaced at close enough intervals to show any significant changes in 



Chapter 3 Field Data Collection and Observation 



