Additional tidal data 



16. In addition to the eight tide gages specifically deployed for this 

 study, data were available from a primary control tide station (33) located 

 inside Los Angeles Harbor and from four pressure sensors located around the 

 harbor perimeter (Figure 2) . These four pressure sensors were installed by 

 CERC to obtain long-term measurements of harbor surge events under a separate 

 subtask of the Model Enhancement Program entitled Wave Data Acquisition. They 

 were configured as low- frequency wave gages, but postprocessing of the time 

 series also produces continuous tidal data. 



17. These data were processed to provide additional boundary conditions 

 for the model and for quality control checking of the primary tide data sets. 



In Situ Currents 



Requirements 



18. The requirement for the in situ current subtask was a 30-day record 

 of the vertical velocity profile at eight locations covering the major tidal 

 exchange openings inside the harbor and at the harbor- complex perimeter. The 

 acceptable resolution for the vertical stratification of the flow field was 

 three points, representing a near-surface, middepth, and near-bottom cell at 

 each site. Desired accuracy in speed and direction was ±0.1 knot and 2 deg, 

 respectively. Samples were needed on a similar frequency to the tidal data, 

 that is, continuous time series at average intervals near 3 min. 



Method 



19. The vertical profiles were obtained by deploying up to three cur- 

 rent meters on a string supported by a surface buoy on a taut mooring. To 

 reduce the risk of ship collision, the gage sites were moved to the sides of 

 major entrances and channels. A total of 19 gages were available for the 

 project. A deployment scheme was selected which increased the total number of 

 sites to nine by reducing the number of meters on a string to one or two at 

 certain sites not expected to have strong vertical gradients, while one meter 

 was kept as a spare. Figure 5 shows the location of each site. 

 Instruments 



20. The current meters were ducted- impeller type with an internal com- 

 pass for direction (Figure 6 and Appendix A) . Velocity is measured by count- 

 ing impeller revolutions over the selected averaging interval , and an 



12 



