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4.0 SUMMARY OF MONITORING RESULTS 



The Oceanographic Measurement Program conducted in the southwest corner of the 

 Portland Disposal Site (PDS) provided accurate, site-specific data on tides and near-bottom 

 currents, water temperature, and turbidity during the period from late February to mid-May 

 1996. Measurements were acquired using a bottom-mounted instrument array deployed in a 

 region of relatively rough topography having a water depth of approximately 60 m. Overall, 

 the 78-day measurement program provided excellent data from which to characterize near- 

 bottom currents and turbidity, and evaluate the physical processes governing bottom sediment 

 resuspension within PDS. The wind, wave, and water temperature data obtained from 

 NOAA buoy 44007 located 6 km southwest of PDS were adequate for assessment of the 

 local climatology, as well as meteorological conditions during the current measurement 

 program. The most significant results of the monitoring program are summarized below. 



Water Column Characteristics 



Vertical profiles of temperature, salinity, and density were acquired at a single location in 

 PDS during three events associated with deployment, servicing, and recovery of the moored 

 instrumentation in February, April, and May 1996, respectively. The February profile 

 revealed a water column that was very weakly stratified, as is typical for the coastal Gulf of 

 Maine in winter. Water property characteristics during late April and mid-May illustrated 

 that relatively fresh and warm water had been introduced to the surface layer, presumably as 

 a result of river discharge. Beneath a moderate thermocline and pycnocline, water properties 

 were nearly constant throughout the lower half of the water column. 



With regard to the vertical density stratification, it is apparent that the entire water 

 column to a depth of 60 m is very weakly stratified throughout winter and early spring, 

 whereas the introduction of relatively fresh/warm waters at the surface during mid-spring 

 causes considerable stratification that may tend to decouple horizontal currents and other 

 transport processes within a two-layer water column. Consequently, downward propagation 

 of storm-generated energy would be most effective during winter and late spring when the 

 water column is nearly void of density stratification. With the onset of spring and summer, 

 the bottom waters will be less free to mix vertically with the upper layers, and the resulting 

 stratification may act as a partial barrier to the energy imparted by storms. 



Surface Wave Climatology 



Time-series observations of winds, atmospheric pressure, surface water temperature, and 

 waves from NOAA buoy 44007 were analyzed to assess seasonal and inter-annual variability 

 in meteorological conditions at PDS from January 1993 through May 1996. 



Oceanographic Measurements at the Portland Disposal Site during Spring of 1996 



