Just how much tidal-flat is there?

Dr. Nial Moores, Birds Korea, February 13th 2015.

Any meaningful discussion on tidal-flat conservation in the Republic of Korea (and elsewhere) needs to be based on best information. At the very least, this best information needs to include the area of tidal-flat that remains.

Measuring tidal-flats is challenging. The area of exposed tidal-flat changes daily according to the lunar cycle, and even air pressure and wind; and reclamation projects in adjacent areas can also lead to changes in tidal cycles, e.g. meaning longer inundation on some days than others.

All the same, as a nation the Republic of Korea is well-aware of the economic importance of coastal fisheries and has multiple well-resourced research bodies. Accurate measuring and monitoring of tidal-flat area is therefore well within both the national interest and national capacity. And according to the National Report to the Convention on Biological Diversity, produced by the national government of the Republic of Korea in 2009, there were still approximately 250,000 ha of tidal-flats remaining nationwide towards the end of last decade. This is encouraging, though quite puzzling, because this estimate of tidal-flat area is not that much smaller than estimates published in the 1990s, even before seawall closure at Saemangeum and Namyang Bay, and reclamation of large parts of Asan Bay and Song Do.

Back in 2010, a small Birds Korea team therefore independently measured the remaining area of tidal-flat nationwide. The team, led by Tyler Hicks, used publicly available high resolution imagery, ImageJ and Arcview, and found only about 110,000ha of tidal-flat remaining in the ROK towards the end of the last decade.

To help decision-makers and planners, we made both our methodology and estimate widely available, publishing it first in Korean and English in the Birds Korea Blueprint in 2010; then as part of doctoral research in 2012; and most recently in Status of Birds, 2014.

To our consternation, our estimate of tidal-flat area seems to have been largely ignored. A paper in Ocean and Coastal Management by leading tidal-flat expert Professor Koh Chul-Hwan (Koh & de Jonge 2014) suggested there might still be 214,000ha of intertidal sand and mud-flats remaining; while the Fifth National Report to the CBD, also published in 2014, repeated the estimate of approximately 250,000ha used five years before.

Were we in Birds Korea wrong?

Sadly, it seems not. A paper in Frontiers in Ecology also published last year by Murray et al. (2014) provides details of measurements of tidal-flat area in the Yellow Sea made through their team’s analysis of Landsat Archive images. Using a different methodology to us, these authors found 120,472ha of tidal-flat remaining in the ROK last decade. This is only 10% more tidal-flat than we found; and less than half of the area estimated to remain in the ROK’s Fifth National Report to CBD.

So let us all agree: there are indeed only approximately 110,000-120,000ha of tidal-flat remaining in the ROK. The nation has lost at least two-thirds of its tidal-flats since the 1950s, and 75% of the historical tidal-flat area. Reclamation still continues at several sites.

The increasingly urgent job at hand is to conserve those areas that remain, and to restore those areas that can be restored. This is nothing new: indeed, these are the very same commitments already made by the nation under the Ramsar Convention and through the CBD’s Aichi Targets.


1. Birds Korea. 2010. The Birds Korea Blueprint 2010 for the conservation of the avian
biodiversity of the South Korean part of the Yellow Sea
. Published by Birds Korea,
October 2010.
2. Koh C-H and V. de Jonge. 2014. Stopping the disastrous embankments of coastal wetlands by
implementing effective management principles: Yellow Sea and Korea compared to the European
Wadden Sea. Ocean and Coastal Management 102, 604-621.
3. Moores, N. 2012. The Distribution, Abundance and Conservation of Avian Biodiversity in Yellow
Sea Habitats in the Republic of Korea
. University of Newcastle, Australia. Unpublished PhD
thesis (in English).
4. Moores, N., Kim A. and Kim, R. 2014. Status of Birds, 2014. Birds Korea report on bird
population trends and conservation status in the Republic of Korea
. Published by Birds Korea,
September 2014.
5. Murray, N., Clemens, R., Phinn, S., Possingham, H. and R. Fuller. 2014. Tracking the rapid loss of
tidal wetlands in the Yellow Sea. Frontiers in Ecology and the Environment. Published by
the Ecological Society of America.
6. Republic of Korea. 2009. Fourth National Report to the Convention on Biological Diversity.
Submitted in May 2009.
7. Republic of Korea. 2014. The Fifth National Report to the Convention on Biological Diversity.
Submitted in April 2014.

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