Best Flooding Prevention in Seattle WA

Quoted to fully clean out culvert pipe, paid $1,300 to have someone spray the inside with a high pressure 3/8 jet fed from a garden hose. Anyone with a pressure washer could do this, I agreed to this quote as it sounded reasonable to properly clean out a 12 concrete culvert pipe as you need to scoop out all sludge and gunk stuck to the walls and floor. Yes the volume of water that comes out of a garden hose flows just fine, but there is still 6 of sediment along the bottom that restricts the flow enough to back up about 3 acres of land when it rains in the winter. When I called to get a refund they said the plumber did what was asked of them. Next time I'll think twice before leaving it to the professionals.