Water Level Records 



Marine (oceanic) coastlines 



Changes in water levels along coastlines have profound influence on the 

 geology, the natural ecology, and human habitation in these regions. Predict- 

 ing and understanding these changes can guide coastal planners in developing 

 rational plans for coastal development and in the design, construction, and 

 operation of coastal structures and waterways. Sea level along open coasts 

 varies in response to many natural processes on various temporal scales. 

 Short-term factors are outlined in Table 14. 



Table 14 



Short-Term Sea-Level Changes Along Open Coastlines 



1 Periodic sea-level changes 



Astronomical tides (diurnal and semidiurnal) 



Long-period tides 



The Chandler effect - changes in the rotation of the earth 



1 Meteorological and oceanographic contributions 

 Atmospheric pressure 

 The effects of winds - storm surges 



The contribution of water density (temperature and salinity) 

 The effects of currents (meanders in western boundary currents) 

 Evaporation and precipitation 

 Ocean surface topography - ocean surface topography changes caused by density 



variations and climatic/current variations 

 El Nino/ southern oscillation 



' Seasonal variations 



Seasonal cycles (Atlantic, Pacific, Indian Oceans) 

 Seasonal variation in slope of the water surface 

 Seasonal water balance of the world's oceans 

 River runoff/floods - influential in inland seas 



' Seiches 



'Tsunamis - Earthquakes and mean sea level 



Tsunamis - Short-term, catastrophic water level changes 

 Earthquakes - Changes in land levels 



(Adapted from Emery and Aubrey (1991) and Lisitzin (1974)) 



Sea level changes over historical and geologic time scales are the subject of 

 active research in the scientific community and the petroleum industry. The 

 study of these changes has been hampered by the poor worldwide distribution 

 of tide gages, as most gages were (and still are) distributed along the coasts of 

 industrial nations in the Northern Hemisphere. Many of the geomorphic fea- 

 tures with which we are familiar on contemporary coasts are the byproducts of 

 the eustatic rise in sea level caused by Holocene climatic warming and melting 

 of glaciers and ice sheets. The Holocene rise in sea level is well documented. 

 Using the existing distribution of gages, it is not possible to assess if the rise 

 is continuing because, while many gages record a recent rise in relative sea 

 level (rsl), an equal number record a fall (Emery and Aubrey 1991). 



92 



Chapter 5 Analysis and Interpretation of Coastal Data 



