MEMORANDUM FOR RECORD: 23 October 1987 



SUBJECT: 15 October 1987 Survey at LA/LB Stations LA-3 and LB-4 



1. As a follow-up to and confirmation of survey work performed, during 

 April in Los Angeles and Long Beach Harbors, additional measurements 

 were made at Stations LA-3 and LB-4. These measurements were made in 

 three stages. The first two were made with diver assistance, measuring 

 from the top edge of the upper pile bracket, down to the harbor bottom 

 and Paros sensor pressure housing diaphragm. The third measurement was 

 made from the top edge of the upper pile bracket, up to a point on the 

 pier, which had been leveled-in previously. Survey bench marks used at 

 LA-3 and LB-4, respectively, were NOAA/NOS bench mark "TIDAL 8" at 

 elevation +13.90' MLLW and Port of Long Beach Civil Engineering 

 Division bench mark "1935" at elevation +15.98' MLLW. 



2. Using the above mentioned bench marks as backsights, elevations to 

 the control points were measured of 13.28' and 15.92' MLLW, for 

 Stations LA-3 and LB-4, respectively. The total distance measured from 

 the control point to the Paros sensor housing diaphragm at LA-3 was 

 30.70' and at LB-4 was 34.15'. Subtracting these distances from the 

 pier elevations, yields a sensor elevation of -17.42' MLLW at LA-3 and 

 -18.23' MLLW at LB-4. By comparison, sensor elevations obtained in 

 April at Stations LA-3 and LB-4 were -17.50' and -18.03' MLLW. The 

 differing elevations from one survey to the next, are due to the 

 inaccuracies of the taped measurements. 



3. As was stated above, the taped measurements were made to the Paros 

 sensor pressure housing diaphragm. This is the point of the oil/water 

 interface, between the diaphragm and the surrounding water. The point 

 on the quartz crystal pressure transducer, at which the input force is 

 sensed, is 0.53' above the diaphragm. Hence if the sensor elevations at 

 each station from both surveys are averaged and then reduced by the 

 transducer offset, the resulting true elevation at Station LA-3 is 

 -16.93' MLLW and at Station LB-4 is -17.60' MLLW. 



Michael D. Dickey 



Civil Engineering Technician 



Prototype Measurement 8 Analysis Branch 



C3 



