There are tidal grids and railways here and still in use. There are ways to arrange them so bottom paint does not escape into the sea. It does take a willingness though of either the management or the gvmt. to set it up and ensure it is used properly.
I have been told of similar setups at other locations so they are not dead. Travelifts are not always viable in some places. Either because grids and railways already exist and just need some mods. or the land is too expensive or not available.
Our old Y.C. still has one, grid, but there are strict rules to ensure it is used properly. Unfortunately there are always a few who think rules don;t apply and were abusing the priviledge so now NO ONe CAN POWER WASH except the club employees. Without that change they would have lost it.
The grid, drydock, is a huge benefit to the members.
Tarkanen Shipyard, Sointula, B.C. has done something similar although with a railway.
Both use a containment ditch which catches all the wash water from power washing, sanding, etc. and then pumps it into tanks where the debris is allowed to settle at which point the water can be removed. The sediment then is dealt with as hazardous waste. Don't know what that procedure is though.
I agree that unless a concerted effort is made to setup properly and keep it that way the railways and grids will disappear.