sion, they say, are simply greater than 

 our means for understanding them. 



Last fall the U. S. Environmental 

 Protection Agency released the results 

 of a study concerning the so-called 

 greenhouse effect, created by the 

 buildup of carbon dioxide in the upper 

 atmosphere, and its presumed in- 

 fluence on sea levels. The most 

 publicized portions of the agency's 

 report were the worst case projections, 

 one of which suggested that sea level 

 could rise off the Carolinas as much as 

 two feet by the year 2040. Such a rate 

 would be four times or more the pre- 

 sent rise, which has been estimated at 

 one-third foot to one foot per century. 



While such a drastic sea level rise 

 might indeed doom the barrier islands 

 of North Carolina, Riggs says the pro- 

 jections are too "iffy" to be useful 

 now. Sea levels rise because of melting 

 ice caps and glaciers, but also, some 

 scientists believe, because of compac- 

 tion in undersea sediments or a gradual 

 sinking of the continental land masses. 



And, while the world's ice has been 

 melting for thousands of years, it 

 seems to have been melting less rapidly 

 recently. Riggs says it is possible that 

 the world is about to experience a shift 

 toward more glaciation and slowly 

 lowering seas. 



"The last four or five times that sea 

 level changed, it changed about now in 

 the cycle, toward more glaciation," 

 Riggs says. 



But "about now" in the context of 

 world geology could mean hundreds or 

 thousands of years. And Riggs says he 

 makes the point not to raise any hope 

 that the sea may stop attacking and 

 retreat soon, but only to illustrate that 

 the greenhouse effect is only one of a 

 number of forces shaping the seas and 

 coasts. 



Another obstacle to understanding 

 beach erosion is that the part of the 

 beach we see is actually only a fraction 

 of what is eroding. And what happens 

 unseen under the wave may have more 

 impact on the beaches than we have 

 thought. 



John Kraft, a geologist at the Uni- 

 versity of Delaware, has been doing 

 Sea Grant research in Delaware's 

 nearshore waters, and has found the 

 beachface there eroding all the way out 

 to 325 yards offshore, in 30 feet of 

 water. 



Kraft says that he and others had 

 assumed that sand placed on the 

 beaches during so-called beach 

 nourishment projects helped restore a 



gentle slope to the underwater 

 beachface by making more sand 

 available to the system. It was partly 

 because of this assumption that beach 

 nourishment has been regarded as the 

 method of choice for beach protection 

 (see page 5). 



But when he took core samples of 

 the sediments under water, Kraft 

 found the sand layer surprisingly thin. 

 Where he had expected to find several 

 meters of sand, he found only one and 

 one-half meters at the thickest. In 

 some areas, old sediments had been 

 laid bare and were eroding. 



Kraft believes the slope of 

 Delaware's beaches is getting steeper 

 because beach managers have decided 

 to hold a line and protect beachfront 

 development. The rising sea, unable to 

 advance at the top of the beach slope, 

 advances instead nearer the foot, and 

 the slope steepens. 



Kraft says that for every meter of 

 elevation lost on the beach berm, ten 

 more are being lost along the length of 

 the beachface under water. He ex- 

 plains that most of the sand added 

 during beach nourishment soon disap- 

 pears into "sediment sinks" far 

 offshore, or in bays and estuaries. 



"Suppose you're a beach manager, 

 and I told you that if you replenished 

 the beaches with three hundred and 

 fifty thousand cubic yards of sand each 

 year, you could keep the beaches 

 stable forever," Kraft says. "You'd 



Photo by Jerry Machemehl 



probably spend the five dollars per 

 cubic yard to do this — at an annual 

 cost of more than one-point-seven- 

 million dollars. 



"But suppose I told you that ten 

 times this amount of sediment is mov- 

 ing along the beaches into Delaware 

 Bay and out on the inner shelf. You'd 

 have to spend ten times as much — 

 seventeen million dollars per year — to 

 keep the beaches stable. You may 

 want to change your mind." 



Kraft says that one danger in 

 holding a line against beach erosion is 

 that the steeper slope of the beachface 

 will increase the risk of property 

 damage during storms. And, because 

 the dry part of the beach seems, to the 

 casual observer, to be stable, some 

 property owners may underestimate 

 their lots' vulnerability. 



"The more you steepen the slope, 

 the closer the average large wave 

 comes to the beach itself, and the more 

 damage it can do," Kraft says. 



Kraft says he would expect to find 

 the same erosion pattern on nourished 

 shorelines in North Carolina. "I think 

 it's happening all over," he says. 



So what can be done about beach 

 erosion? The obvious answer, to some, 

 is, don't fight it, retreat: Build 

 moveable houses; build far back from 

 the sea, or don't build on barrier-island 

 beaches at all. Perhaps the most- 

 quoted proponent of this view is Orin 

 Pilkey, a Duke University geologist. 



This beachfront home was undermined by a 1973 northeaster' 



