plap

Imitative, or perhaps a blend of plash +‎ flap.

plap (third-person singular simple present plaps, present participle plapping, simple past and past participle plapped)

1. To plash; fall with a plashing sound
   • 1859, William Makepeace Thackeray, The Roundabout Papers:

     On this day it was so cold that the white bears winked their pink eyes, as they plapped up and down by their pool, and seemed to say, " Aha, this weather reminds us of dear home!

   • 2010, Joanne Harris, Blackberry Wine:

     He'd have to look up, have to look— A stone plapped into a greasy puddle not two feet away.

   • 2015, Harold Pinter, The Dwarfs:

     The crowd humped together, squealing, around her, to the floor; the room plapped into halflight, low from two wall lamps, glowing on her legs, over the ducking heads.

• plop

• Appl., Lapp, appl., palp