I am using the word 'sediment' quite a lot for my research. I work in the field of river engineering and I always thought 'sediment' to be uncountable.
However, a colleague uses 'sediments' to mean different grain classes, e.g. instead of writing 'sand, silt, cobbles, and pebbles deposit in the river' he would write 'sediments deposit in the river'.
I believe this use is correct, but I also think that if one generally means 'material being transported in a river' should use 'sediment' singular, e.g. 'sediment is being transported in the river' and not 'sediments are being transported in the river.
Do you agree that in the first sentence the word 'sediment' includes all the possible grain classes that are transported in a river?