The literary device which is used in this sentence "the trickle, trickle, trickle of the creek water was soothing." is onomatopoeia.
Onomatopoeia refers to the literary device which names the action or the thing through its vocal imitation or the sound associated with the object or person.
On identifying with the above sentence, word "trickle, trickle, trickle" imitate the sound of the water which was soothing.