http://news.sciencemag.org/environment/2014/08/how-old-litter-beach

How old is that litter on the beach?

By Ian Randall 18 August 2014 5:00 pm

One person?s trash is another person?s science. That?s the idea behind
new research that uses litter left behind by extreme floods to help plan
for similar hazards in the future. Once dumped into the environment,
litter is subject to natural transportation processes and typically ends
up in the sea, forming gyres of marine debris. While most of it
ultimately sinks to the sea floor, a significant portion is washed up
onshore, adding to the ?wrack lines? of driftwood, kelp, and other
natural flotsam deposited at high-tide marks. Extreme flooding
events?such as those caused by tsunamis or storm surges?can also leave
behind wrack lines. Now, researchers have proposed that these wrack
lines could be used to identify past floods and map out their impact,
thereby providing information on flooding in remote regions for which
significant data are not usually available. Litter has an advantage over
natural flotsam for this purpose, because trash often tells you how old
it is: Just look for the production or expiration dates on discarded
packaging. Because wrack lines containing trash must have formed after
the most recent date found on the litter, scientists realized they could
use that information to roughly date the flood that caused a particular
wrack line. To demonstrate their idea, the researchers used GPS to map
out litter deposits along the coastline near the city of Ras al Hadd in
eastern Oman?a region vulnerable to both tsunamis and cyclone-induced
storm surges. They identified two extensive wrack lines of litter (one
of which is pictured) located as far as 900 meters inland. The youngest
trash in each of the wrack lines was stamped with production dates of 9
January 2007 and 31 March 2010, respectively. That means the wrack lines
likely originated in the floods caused by cyclones Gonu and Phet, which
occurred slightly later in those same years, the researchers say. By
knowing the maximum water level of past flooding episodes within a
particular region?and how often floods occur?scientists can better
predict the extent and impact of future floods, informing the
development of worst-case scenarios, evacuation plans, and possible
relief efforts.