LU 

 > 



UJ 



_l 



z 



LU 

 CO 

 LU 

 DC 



LU 

 CD 



Q. 

 LU 

 Q 



-25 -20 -15 -10 



YEARS BEFORE PRESENT 



(Thousands) 



Figure 31 . 



Late Quarternary sea level curves inferred from radiocarbon-dated sannples 

 along the U.S. coastlines (modified from Dillon and Oldale 1978) 



Over shorter time scales, tides and storm surges are important in under- 

 standing geomorphic changes. In order to obtain continuous data at a specific 

 site, water level recorders have to be deployed. If fewer data are required, 

 high and low tidal predictions can be obtained from tide recording stations. 

 However, in some locations, the discrepancy between predicted and actual 

 tides on coastal areas only a short distance apart may be considerable. A 

 method for tidal adjustment between predicted tides at a station and those at a 

 nearby study area can be obtained even if only short-term site measurements 

 are available (Glen 1979). 



Sea level also shows pronounced seasonal changes, with some locations 

 differing by 1 m annually from the highest to the lowest monthly values 

 (Komar 1976). Around the United States and in most locations worldwide, 

 for example, sea level is lowest in the spring months and highest during the 

 late summer and autumn. A number of factors are responsible for these 

 seasonal deviations, including changes in water temperature, salinity, atmo- 

 spheric pressure, river runoff, and longshore winds. 



The National Ocean Service of the National Oceanic and Atmospheric 

 Administration (NOAA) is responsible for monitoring sea level variations at 

 115 stations nationwide (Hicks 1972b). The Corps of Engineers District 

 offices located near the coast also collect tidal elevation data at additional 

 locations. Daily readings are published in reports that are entitled "Stages and 

 Discharges of the (insert location) District." 



72 



Chapter 4 Investigation of Environmental Factors 



