bench mark monuments placed for this study remain serviceable and did 

 not require any repair during the term of the study. 



2 . Prof i le Surveys . 



Beach profile surveys were accomplished in two parts on the same 

 day: 1) the backshore and upper foreshore were measured from the bench 

 mark out to wading depths, on the low tide; and 2) the offshore part of 

 the profile was measured with a fathometer on a boat seaward from the 

 breakers, on the high tide (Figure 3). By doing the monthly surveys on 

 the date of maximum spring tidal range during daylight hours, overlap 

 of the two parts of the survey was usually achieved. High waves and 

 winds complicated the survey operation and introduced errors into the 

 fathometer survey of the offshore profile segment. 



The land survey of the backshore and foreshore was done using a 

 transit, surveyors rod, and tape. Elevations were measured to 0.01 foot 

 (0.3 cm) and distances to 0.1 foot (3 cm). Alinement along the range 

 line was achieved by using flags to mark the two bench marks on the 

 range. Rod stations were measured at 10-foot (3 meters) intervals sea- 

 ward of the bench mark except where pronounced changes in the slope occur. 

 Measurements were made out into the water by the tapeman paying out the 

 tape in 10-foot (3 meters) increments from a fixed point at the water 

 edge. The land survey was terminated when the water became too deep 

 for the rodman to wade or the breaking waves made it impossible to plumb 

 the rod. 



The offshore part of the survey was done with a Raytheon Model 

 DE719 survey fathometer used from a 16-foot boat. This is a portable 

 survey fathometer that allows for calibration to specific oceanographic 

 conditions of seawater temperature and salinity and is an ideal instru- 

 ment for the survey depths of this study. 



However, use of a survey fathometer for measuring beach profiles on 

 the ocean involves additional errors inherent in reducing the fathometer 

 data to an actual bottom profile. These errors are due to the effect of 

 waves, tide, relation of transducer to water surface, etc., involved in 

 correcting the raw fathometer readings to the profile soundings. Saville 

 and Caldwell (1953) evaluated the accumulated acoustic sounding error 

 involved in measuring beach profiles with a fathometer by making repeated 

 soundings of a single profile over a short period of time, and comparing 

 them to lead line soundings. Their results show that the probable error 

 in this survey method is less than 0.5 foot (15 cm). Thus, it is thought 

 with proper calibration and suitable care in reducing the data, that an 

 accuracy of ±1 foot (±30 cm) was possible in using a fathometer for 

 the offshore profile measurements. 



Positioning of the boat during the offshore part of the profile 

 survey was performed by a range and horizontal sextant angle system 

 similar to that employed by Inman and Rusnak (1956) . Each range line 



12 



