After the instrument is leveled, a backsight (BS) reading of the level rod 

 on the TBM is taken and the instrument height (HI) is computed. This compu- 

 tation is necessary to determine if turning points (TP) are required and at 

 what relative elevation the survey datum (mean sea level, mean low water, etc.) 

 will be reached. The distance from the TBM to the instrument is then measured 

 using the level rod. 



The instrument should be checked frequently during the survey to ensure 

 that it remains level. If the instrument becomes out of level, it must be re- 

 leveled immediately and a notation made in the fieldbook. After the profile 

 is completed, a new backsight reading must be taken to establish the height of 

 the instrument for that section of the profile surveyed after the instrument 

 was releveled. If the point at which the instrument was determined to be out 

 of alinement is unknown, then the profile must be resurveyed. 



2. Survey Line . 



The profile is surveyed to the survey datum (or farther) with elevation and 

 stadia readings taken at every change in slope or e^^ery 30 to 50 feet or 9.1 to 

 15 meters (15 to 20 paces) . Since the RP selects the points (stations) which 

 define the profile, it is Important that the points be carefully cinsen (par- 

 ticularly in the dune area) to obtain an accurate cross section of tp.e beach. 

 Points at the high water line and at the edge of the swash zone should be taken 

 and noted. As a check on the stadia measurement, the distance between succes- 

 sive stations on the beach face should be paced by the RP. At each station, 

 the RP should: 



(a) Signal the number of paces using the hand signals given in 

 Table; 



(b) move to an online position, as determined by the instrument 

 and range poles; 



(c) stand facing the IP with rod held vertically (as determined 

 by the circular rod level) until the IP signals either completion 

 of the station data or of the profile survey; and 



(d) on stations closer than 20 feet (6 meters) to the instrument, 

 the level rod should be used as a tape to measure the distance 

 directly. 



3. Turning Point (TP) . 



During a survey, the instrument may have to be moved to another point on 

 the profile line when: 



(a) A change in elevation is greater than the full length of the 

 level rod; 



(b) the distance surveyed is greater than 250 to 300 feet (80 to 

 90 meters), the limit for accurately reading the stadia distance; 



(c) high wind conditions cause the upper section of the rod to 

 bend, reducing the accuracy of the readings; and 



(d) the Sun is behind the rod making the numbers difficult to 

 read. 



