Completely uniform through sediments (7)

I believe the answer is:

alluvia

I'm a little stuck... Click here to teach me more about this clue!

'sediments' is the definition.
Although both the answer and definition are plural nouns, I don't see how one could define the other.

'completely uniform through' is the wordplay.
'completely' becomes 'all' (synonyms).
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'through' becomes 'via' (I've seen this before).
'all'+'u'+'via'='ALLUVIA'

Can you help me to learn more?

(Other definitions for alluvia that I've seen before include "Clay, silt deposits left by flowing water" , "deposits laid down" , "Material from river beds" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.