A drift line is an area normally in a continuous line which occurs when waves flow back from the beach leaving floating elements on the water edge which rode in on them. On this photo one can clearly see a drift line of microplastic:
Every wave deposits a line of rubbish, sometimes the drift line flows back into the sea and is washed up again with the next wave. At high tide the line is at the top of the beach.
This is how floating elements or ones in the sea and ones which are moved by waves get washed up on to the coastline.
Drift line monitoring is done according to a given scheme; the rubbish washed up is counted, documented, collected and disposed of professionally.
Under OSPAR drift line monitoring selected coastal areas are checked on a regular basis (OSPAR is short for „Oslo“ and „Paris“ and is an international agreement for the protection of the North Sea and the North East Atlantic). The above mentioned result is as follows in data:
OSPAR drift line monitoring along the coast of the southern North Sea (2002-2008):
The amount of plastic collected worldwide in beach rubbish collecting drives varies depending on locality between 60 and 90%.