Getting down to the nitty-gritty of building on sand 



The problem: predicting erosion rates and dispos- 

 ing of sewage in sandy coastal soils 



Sand. It moves, washes, blows and erodes. And it is not 

 always the best soil under permanent structures or 

 waste-treatment systems. 



Many who own beachfront property risk loss or 

 damage to their homes, either because of rapid beach ero- 

 sion during storms, or because of long-term recession of 

 the shoreline. In both cases, the loss of sand can mean un- 

 dermined foundations, collapsing buildings. State of- 

 ficials are trying to find ways to protect both the 

 property and the property owner. But they lack some 

 key information about what parts of the shoreline are 

 most vulnerable. Few reliable guidelines are available to 

 predict how beachfront land might erode during severe 

 storms. 



Sand is also a culprit in the problem of sewage disposal. 

 Conventional septic systems perform poorly where soils 

 are porous and water tables are high. To compound the 

 problem, the freshwater "lenses" that supply many of 

 our barrier islands with drinking water may sometimes 

 be tainted by effluent seeping through the soil. Island 

 communities have often viewed alternatives to septic 

 systems as either too expensive (ocean outfalls and cen- 

 tral treatment plants) or too restrictive (outright bans on 

 new construction). State agencies need hard facts to help 

 them protect the quality of drinking water, and also the 

 quality of nearby estuaries and shellfishing grounds. 



The research: to develop models that will predict 

 erosion and to test alternative waste disposal 

 systems in the shallow sandy soils of the barrier 

 islands 



On the beachfront, John Fisher, Margery Overton and 

 Spencer Rogers will study the problems of short-term 

 erosion. So far, the complex interplay of storm waves, 

 storm surge and sediments has not yielded to the tools of 

 numerical "modeling." To develop such models, Fisher's 

 team will compile erosion records from a number of 

 barrier-island storms, and will use them to test and 

 perhaps improve the formulas used now for predicting 

 long-term erosion. The results will help state officials 

 evaluate the level of risk for many coastal structures and 

 building sites. The study will also help improve the 

 design criteria builders and architects use for beachfront 

 construction. 



Sea Grant research into the problems of failing septic 

 systems and the viral contamination of shellfish has 

 already created something of an underground revolution 

 in the Southeast. Research by Bobby Carlile led to the 

 development of two "alternative" septic systems that of- 

 ten work where conventional systems fail, in the stub- 

 born, wet clays along estuarine shorelines. Coupled with 

 Mark Sobsey's studies of viral contamination, the 

 research showed that effluent could be controlled and 

 treated without endangering shellfish in nearby waters. 



Photo by Steve Murray 



One beach losing sand 



Communities as far away as Texas now employ the 

 designs to help solve their own waste-treatment 

 problems. (Two manuals on the design of these systems 

 are available from UNC Sea Grant.) 



This year, continuing research by Craig Cogger, who 

 assisted Carlile on the earlier project, is extending the 

 study to the coarse and sandy soils of the barrier islands. 

 Cogger is testing the designs, which employ low-pressure 

 pumps to "dose" effluent evenly into shallow soils, to see 

 how much vertical separation is required between the 

 pipes and water tables. Meanwhile, Sobsey continues to 

 monitor the sites, tracing the movement of harmful 

 viruses through the soils. The results should help officials 

 set guidelines for the use of so-called on-site treatment 

 systems. And, some island homeowners may eventually 

 have safer, more-effective waste-treatment systems. 



The researchers: 



John Fisher, Department of Civil Engineering, North 



Carolina State University 

 Margery Overton, Department of Civil Engineering, 



North Carolina State University 

 Spencer Rogers, coastal engineering specialist, UNC Sea 



Grant 



Craig Cogger, Department of Soil Science, North 



Carolina State University 

 Mark Sobsey, Department of Environmental Science 



and Engineering, University of North Carolina at 



Chapel Hill 



