But it does appear to have currency in scientific writing, if Google is any guide. And I quote this footnote:
"On 'confluescence'…when liquid containing solid matter in suspension gathers together and becomes stationary, the solid matter separates out and is deposited. He further suggests that the notion of underground confluescences of water, and in general of underground caverns, prominent in various aspects of ancient Greek physical theory, 'was a natural supposition for men living among limestone mountains'…and that the processes of filtration and confluescence reflect the use of sifting and panning in ancient metallurgy."
(Theophrastus of Eresus: Sources for His Life, Writings, Thought, and Influence)
My Chambers Dictionary of Science and Technology (1971, a good year) includes the presumably related confluent: (Bot.) Said of two or more structures which, as they enlarge, grow together and unite.