Just use forklifts to drop the barrels over the rail of the bridge. The protestors can go along with the barrels or not, makes no difference to me.
The fact is that if a non-cop even touches one of these pukes, that person will be arrested.
I’m thinking front-mounted sprayers (similar to windshield washers) spraying sugar water. And a container of hornets with a blower to blow them onto the protestors.