river crossing button

[wulfir]

I made a map where water was not going to be an issue, but then changed my mind and now I want the troops to be given inflatable rafts (so the player won't be entirely reliant on bridges/barges).

IIRC there is a button for changing 'regular' maps into beach assaults, is there one for making a map into a river crossing without having to expande all streams into wide rivers?