The root ᴹ√SPAL with extended form ᴹ√SPÁLAS appeared in The Etymologies of the 1930s as a variant of ᴹ√PHAL(AS) (Ety/SPAL). Given that both ᴹ√SPAL(AS) and ᴹ√PHAL(AS) produce the same results in both Quenya and Noldorin, it is had to say which derivatives belong to which root, but Ilk. espalass and ᴹT. spalasta- are definitely from ᴹ√SPAL(AS) (Ety/PHAL; EtyAC/PHAL). This root is likely a later iteration of unglossed ᴱ√Palas or ᴱ√Palat from the Qenya Lexicon of the 1910s, where Tolkien indicated it was related to ᴱ√PḶTYḶ “✱strike; flat of the hand” (QL/72); it had derivatives like ᴱQ. palasse “foam, splashing” and ᴱQ. palasya- “splash, foam” (QL/72), and it might be related to G. osp(a) “foam” from the contemporaneous Gnomish Lexicon (GL/63).
In general, however, Tolkien used √PHAL (earlier ᴱ√FALA) much more regularly as the basis for wave/beach/foam words.
The Elvish words for “foam” were establish very early, retaining forms similar to Q. wingë and S. gwing throughout Tolkien’s life. The earliest basis for these words were the (unglossed) roots ᴱ√GWIŊI and ᴱ√GWIGI in the Qenya Lexicon of the 1910s with derivatives ᴱQ. winge (QL/104) and G. gwing “foam”, the latter also connected to G. uin “whale” via ancient uı̯u (GL/45).
In The Etymologies of the 1930s Tolkien gave the root as ᴹ√WIG with derivatives ᴹQ. winge and N. gwing, all of the same basic meaning. The continued appearance Q. wingë and S. gwing in Tolkien’s later writings indicates the continued validity of this root, but the related verb Q. winta- “scatter, blow about” (PM/376 note #6) hints the root may have become √WIÑ, or at least had such a variant. In notes from 1968 Tolkien’s considered having gwing along with ross “spray” be loan words from Beorian (PM/368, 371), but he ultimately abandoned this idea (PM/376 note #6); see the entry on √ROS for further discussion.