Plans worked up by the Metrotidal consortium of consultants Capita Symonds and EC Harris and architect Bluebase include a 7.6km road and rail tunnel linking reclaimed land off Canvey Island to Medway in Kent.
The crossing will be incorporated with a flood barrier and a lagoon on the Kent side of the river where a tidal power plant would be built. The project also includes a £1bn immersed tube road and rail tunnel.
The tunnel was worked up by consortium member Capita Symonds which has previously worked on immersed tubes for the Øresund Crossing between Denmark and Sweden and the Medway Tunnel.
Above the tunnel, a flood barrier will span from Canvey Island to a newly formed lagoon off the Kent side of the estuary at
Four massive concrete caissons will be built to form a "throttle" for the flood barrier, greatly reducing the tidal range further upstream.
Under Metrotidal's plans, the flood barrier would be funded from the government's emerging flood defence budget.
Finance for the tunnel and tidal power plant would come from road tolls from vehicles using the tunnel that would link the A13 and A130 in Kent with the M2, and tariffs paid by the rail operators.
However, the plans have been slammed by the Royal Society for the Protection of Birds which claimed it would cause "potentially irreparable damage to the mudflats and grazing marshes that tens of thousands of birds depend on for food and shelter during the winter".
The Department for Transport signalled last week that a new Thames Crossing will now be formally studied after it appointed Parsons Brinckerhoff to come up with a shortlist of detailed options for a new crossing.
Essex and Kent County Councils had been on the point of launching their own £100,000 study into a new crossing (NCE 7 February).