"Models can be a hazard to society, and this is certainly an example of such," wrote Orrin Pilkey of Duke University's Nicholas School of the Environment and Earth Sciences, and J. Andrew Cooper of the Coastal Research Group at the University of Ulster in Northern Ireland, in a Perspectives commentary.
The mathematical equation, called the Bruun rule, "is a 'one model fits all' approach unsuitable in a highly complex natural environment with large spatial variations in shoreline retreat," the two authors added. "Even under ideal conditions ... the rule has never been credibly shown to provide accurate predictions."
Pilkey, a retired geology professor who still directs Duke's Program for the Study of Developed Shorelines, said in an interview that the rule was developed in the 1960s by Per Bruun, a Danish civil engineer who was long active in Florida beach preservation projects.
According to Pilkey, the Bruun rule stipulates that it is the slope of the "shoreface" -- the broad front of a beach extending down into the water to a depth of about 10 yards -- that controls how and how quickly a beach "erodes," meaning how it retreats landward as sea level rises.
"There is no relationship between the shoreface slope and the rate of erosion," he said. "We know that each shoreline is different, and one model cannot possibly explain every shoreface. It's ludicrous. And yet it's being defended by a number of people."
Their commentary also said the Bruun rule is intended "to be deployed only under a limited range of environmental circumstances (such as uniform sandy shorefaces with no rock or mud outcrops). Unfort
Contact: Monte Basgall