What's the difference between alluvion and alluvium?

Alluvion

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Definition:

• (n.) Wash or flow of water against the shore or bank.
• (n.) An overflowing; an inundation; a flood.
• (n.) Matter deposited by an inundation or the action of flowing water; alluvium.
• (n.) An accession of land gradually washed to the shore or bank by the flowing of water. See Accretion.

Example Sentences:

Alluvium

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Definition:

• (n.) Deposits of earth, sand, gravel, and other transported matter, made by rivers, floods, or other causes, upon land not permanently submerged beneath the waters of lakes or seas.

Example Sentences:

• (1) However, Corbicula from several tributaries draining alluvium derived from the Sierra Nevada had lower As concentrations than would be predicted by the relation developed for perennial flow sites of the San Joaquin River.