Scraped (river bottom)

• Unearthed, with "up"
• Scraped the bottom of
• Brought (up), as from the distant past
• Dipped in flour
• Sprinkled with flour
• Changed channels, in a way
• Hauled up (from depths)
• Made deeper, as a shipping lane

Wiktionary Word definitions in Wiktionary
vb. (en-past of: dredge )