merse

plural merses

1. Alluvial, often marshy land by the side of a river, estuary or sea.

   1 more example

   Owing probably to the channel lying obliquely to those mud flats, the flood rushes up the river with a bore, the front wave of which may be several feet high. As a result, the loose mud is churned up by every tide and the water that inundates the merse always contains much mud in suspension. Consequently the merse must be continually increasing in height. That the siltings may be rapid in favourable circumstances is shown near Kirkconnell where mooring bollards are seen […]

   1926, The Journal of Ecology, volumes 14-15, page 312