forces assault the buildings there. The 

 surge itself lifts many structures, which 

 are bouyant, right off their founda- 

 tions. The water, as it passes, also 

 creates a "form drag," a force that tries 

 to tug the building along with the flow. 

 Once the building is freed from its un- 

 derpinnings, it too becomes a destruc- 

 tive force. 



Machemehl describes the scene as a 

 large storm surge moves ashore: 



"Those structures on slabs would 

 tend to be picked up and floated away, 

 and they would become battering rams 

 against the other structures. The beach 

 profile would recede, and some of the 

 structures on piles would overturn 

 because their pile foundations were 

 not deep enough. As the surge came in, 

 the exterior walls of many buildings 

 would be destroyed." 



How will the state's coastal 

 buildings fare during all this lifting, 

 dragging, smashing and blowing, the 

 next time a hurricane comes? Not well, 

 Machemehl says. 



"Some of our structures, maybe fifty 

 to sixty percent, would be destroyed in 

 a one-hundred-year-frequency storm," 



he says, "and possibly all of them with 

 a two-hundred-year-frequency storm." 



The "two-hundred-year storms," 

 the extreme hurricanes like Camille, 

 show up every couple of centuries. 

 They leave very little trace of civiliza- 

 tion in their wakes. Engineers don't 

 even bother designing structures to 

 resist them. 



"It would be impossible to design 

 and build a structure that would sur- 

 vive all events," Machemehl says. 



The building most likely to survive 

 an extreme hurricane would be one of 

 cast concrete (not concrete blocks), 

 reinforced with steel. Something like a 

 bunker or a pillbox. But not many peo- 

 ple want to spend their vacations in 

 pillboxes, and concrete and steel, while 

 practical for large motels and hospitals, 

 are far too expensive to be used exten- 

 sively in houses. 



Building almost anything within 

 reach of the sea is a risk many have 

 found worth taking partly because of 

 federal flood insurance. 



Federal flood insurance was begun in 

 1968 and is available for buildings in all 



the nation's flood-prone areas. Since 

 the program offers, through private 

 companies, low-cost insurance in high- 

 risk areas, it has helped encourage 

 development at the coast. To qualify 

 for coverage, new buildings have to 

 meet only one requirement: floor eleva- 

 tions must be above the expected surge 

 during a "100-year storm." Buildings 

 constructed before 1968 qualify 

 automatically, with no elevation re- 

 quirements. 



But Machemehl believes that just 

 because a building qualifies for in- 

 surance doesn't mean it's a reasonable 

 risk. 



"I think the contractors, the 

 engineers and architects must accept 

 their responsibility to refuse to design 

 and build inadequate structures on the 

 coastline," he says. "That insurance 

 program is a program underwritten by 

 the government. So that if there's great 

 destruction in an area because of the 

 quality of construction, then, in 

 general, everybody pays for it." 



Machemehl says builders weaken 

 structures by using too few metal 

 anchors, by using paper or "fiber- 



board" rather than wood or plywood 

 for sheathing, by using piles that are 

 too shallow, by skimping on roofing 

 materials and by failing to adequately 

 secure porches, overhangs, awning and 

 corners. 



Since it became necessary to elevate 

 new beach residences in order to meet 

 insurance requirements, wood pilings 

 have sprouted like forests under new 

 houses at the beach. 



"The reason to put a house on piles 

 is to get up above the storm surge," 

 Machemehl says. 



Most of the state's new beach houses 

 have an elevation of sea level plus 12 

 feet — just enough to clear another 100- 

 year storm like Hazel, whose surge 

 reached 11 feet. Piles also have the ad- 

 vantage of allowing water to pass un- 

 der the building, and so don't absorb 

 much of the force. Wall foundations, 

 especially those of concrete block, per- 

 form very poorly during hurricanes. 



Almost as soon as he began putting 

 together his picture of buildings in 



coastal hazard zones, Machemehl 

 found several pieces missing. 



There were, for one thing, no reliable 

 data on the pressure exerted by waves 

 cresting against the floor of a building. 

 So an NCSU graduate student, under 

 Machemehl's direction, began using 

 scale models, a mechanical wave tank 

 and electronic pressure transducers to 

 determine wave uplift under buildings. 

 Machemehl believes that when the 

 study is finished, sometime this year, 

 information will help designers deter- 

 mine how strong floor structures and 

 their connections to piles must be to 

 resist waves. 



Missing, too, was information on the 

 speed and extent of erosion likely dur- 

 ing storms on the coastline — 

 information vital to engineers trying to 

 calculate how deep piling foundations 

 should be. 



"Right now, nobody can say how 

 deep piles should be," Machemehl 

 says. "Some say eight feet below the 

 profile, but that may not be deep 

 enough." 



Machemehl has been devising a 

 numerical model that could project the 

 rate of erosion for building sites along 

 the coast. 



In another Sea Grant study, Stan 

 Riggs, Mike O'Connor and Vince Bellis 

 of East Carolina University found 

 ways to predict how susceptible es- 

 tuarine shorelines are to erosion. Their 

 methods for predicting erosion are 

 described in a flyer, "Relative Es- 

 tuarine Shoreline Erosion Potential in 

 North Carolina," which is available 

 from the Sea Grant office in Raleigh. 



But even though there are still ques- 

 tions to be answered, the profile of a 

 durable beach structure is already 

 clearer: The building site should be 

 well behind the primary dunes. The 

 pile foundation should reach at least 8 

 feet into the profile of the shoreline, 

 not including the depth of the dunes. 

 Piles should be bolted to the floor 

 structure. Walls should be braced with 

 rigid wood or plywood sheathing. All 

 corners, overhangs and other 

 windcatchers should be well-anchored. 

 And the whole building should be tied 

 together with metal connectors. 



Of course, the most hazardous 

 building sites are generally those on the 

 beachfront, where erosion and wave ac- 

 tion are most intense. But even sites 

 several blocks from the shoreline are 

 vulnerable to flooding, winds and 

 floating or blowing debris. 



"The exterior walls of many buildings 

 would be destroyed" — Jerry Machemehl 



