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10. SEDIMENTARY PROCESSES IN THE ESTUARINE REGION 



10 . 1 INTRODUCTION 



There have been drastic changes in the world's shorelines since the 

 retreat of the last ice age. Over the past -6,000 years, the rate of rise 

 of sea level has been relatively low (0.08 m/100 yr) compared to the period 

 -20,000-6,000 BP (0.8 m/100 yr) (Fig 7.1). It is not surprising, 

 therefore, that many of today's estuaries have been "around" approximately 

 in their present configuration only in the past few millennia. Even in the 

 absence of sea level change, estuaries are highly dynamic and in many ways 

 reflect the type of macro-scale processes characteristic of oceans. 

 Estuarine shorelines change under the action of hydrodynamic forcing and 

 associated sediment transport. Where sediments play a recognizable role, 

 estuaries almost never attain true hydrodynamic/sedimentary equilibrium. 

 Usually there is a quasi-equilibrium characterized by long-term changes in 

 the bottom bathymetry. An important issue posed by potential effects of 

 sea level rise pertains to our ability to predict various facets of 

 estuarine response to sea level rise, including shoreline configuration, 

 bottom sedimentation and marsh development/degradation. 



10.2 SHORELINE CONFIGURATION 



Much of the knowledge of shoreline changes is based on geological 

 evidence which has been used to develop scenarios for estuarine formation, 

 development and eventual demise. Two edited volumes by Schwartz, Spits and 

 Bars (1972) and Barrier Islands (1973), are collections of important papers 

 in the subject area. Spits and Bars covers seventeen papers, from 1890 to 

 1971. Barrier Islands covers forty papers, from 1845 to 1972. 



A more recent set of papers (also of geological nature) edited by 

 Leatherman (1979) shows that there is new emphasis on descriptive modeling 

 of barrier island and inlet morphologic changes, much of it based on 

 holocene shoreline recession evidence. Reference must also be made to a 

 series of papers recently edited by Nummedal et al . (1987) on shoreline 

 response to sea level change. 



