There are subcontractors that deal with bypassing, solely. They will supply the piping, fittings and emergency pumps. I've recommend Godwynn if they're in your area.
A culvert can be blocked using sheet metal, plywood barriers, or inflatable culvert plugs.
Plywood and/or sandbags can also be used as culvert blocks, but are more labor-intensive and pose a higher potential for injury. A wood block may require a headwall with kickers oriented to support the boards or plywood. Place the blocking materials over the upstream end of the culvert.
