series is converted to a depth time series by using a conversion factor based 

 on average temperature and salinity, since their variance over the study 

 period did not warrant a time synchronized adjustment in density. The factor 

 used in the conversion was 2.246 ft/psi. 

 Datum assienment 



54. The required datum for all tidal time series was MLLW. Since it 

 was impractical to level each gage from shore using traditional surveying 

 techniques, a simplifying assumption was made that the average free surface 

 elevation over the deployment interval was constant throughout the harbor re- 

 gion. This is valid over a limited area with insignificant freshwater inflow 

 and where no net transport can occur within the area over the time interval. 

 Each tidal depth time series had the average depth of that time series sub- 

 tracted, converting it to a time series relative to the average free surface 

 at that site over the deployment interval. 



D(t) = d(t) - d(t) (1) 



where D(t) is the "de-meaned" time series and d(t) is the measured- depth 

 time series. Under the assumption above, D(t) is referenced to the same 

 datum for all gages. To convert the depth time series to a tidal time series, 

 T(t) , relative to MLLW, a constant equal to the difference between the aver- 

 age free surface elevation over the measurement interval and MLLW, can be added 

 to the depth time series. 



55. Mean Sea Level (MSL) and MLLW are defined as the arithmetic mean 

 elevation of the sea surface and of the lower low water heights, respectively, 

 observed over a specific 19-year metonic cycle (Harris 1981) . Means calcu- 

 lated over shorter intervals will vary and are calculated by the National 

 Ocean Service (NOS) for monthly (m) and annual (a) departures from MLLW at 

 each primary control tide station. Thus an average free surface elevation for 

 the deployment interval is not necessarily MSL. 



56. A primary tide station, 33, is located in Los Angeles Harbor 

 (Figure 2) . Its tidal record is referenced to MLLW datum. If the exact ele- 

 vation of the free surface at any time and place relative to MLLW was of pri- 

 mary importance, then the average monthly departure, m , of Gage 33 would be 

 the required constant. However, since the monthly average varies, its use as 

 a constant would produce discontinuities in the records each month. 



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