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Webster 1913 Edition

Adj.

Becoming shallow gradually.

“A shoaling estuary.”

Lyell.

shoaling

shoaling ‎(plural shoalings)

The formation of a shoal.
- 1946, William Vernon Brelsford, Fishermen of the Bangweulu Swamps
  A thorough survey showing depths of channels and lagoons and seasonal directional flow of currents will be necessary for proper fish research because these factors affect seasonal movements and shoalings.