237 



Louis H. Motz 



Department of Civil Engineering 



University of Florida 



Gainesville, FL 32611 



SECT. 8. REVIEW OF IMPACTS OF SEA-LEVEL RISE ON GROUNDWATER RESOURCES 

 Introduction 



In coastal aquifers, groundwater flows from inland recharge areas 

 to discharge areas at or near the coastline. Due to the presence of 

 seawater in the aquifer formation under the sea bottom, a zone of contact, 

 or interface, is formed between the lighter fresh water and the underlying, 

 heavier seawater. The location of the interface is determined by the 

 physical and hydraulic properties of the aquifer, the amount of recharge 

 and flow in the aquifer, and whether pumping from inland well fields 

 reduces the slope of the piezometric surface and the seaward flow of 

 fresh water. A rising sea level will cause the saltwater- freshwater 

 interface to move inland, increasing the salinity of coastal aquifers and 

 threatening coastal well fields. Measures such as hydraulic or physical 

 barriers may protect coastal aquifers in some cases, but abandonment and 

 moving farther inland may be the only reasonable, economical solution in 

 other cases. 



Hvdrologic Setting in Florida 



Impacts of Previous Higher Stands of the Sea . Pleistocene-age 

 shorelines that occur at elevations higher than present-day sea level serve 

 to indicate that sea levels have been higher during some periods in the 

 past. In Florida, at least four Pleistocene shorelines are recognized 

 (MacNeil, 1950): the Okefenokee [150 ft above mean sea level (MSL) ] , 

 Wicomico (100 ft above MSL), Pamlico (25-35 ft above MSL), and Silver Bluff 

 (8-10 ft above MSL) shorelines. The Silver Bluff shoreline is correlated 

 with the climatic optimum, a period approximately 9100 years before the 

 present, when the temperature was about 5°F higher than the present and sea 

 level was on the order of 10 ft higher than the present sea level (Brooks, 

 1970). 



