Coated in flour

• Scraped (river bottom)
• Unearthed, with "up"
• Saved from obscurity, with "up"
• Brought (up), as from the distant past
• Sprinkled with flour
• Scraped the bottom of
• Dipped in flour
• Deepened, as a canal

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