silt upvi phrasalphrasal verb, intransitive: Verb with adverb(s) or preposition(s), having special meaning and not taking direct object--for example, "make up" [=reconcile]: "After they fought, they made up."
(become filled with silt) (泥沙)
淤积,淤塞
It took about 50 years for the harbour to silt up.