You can always use an old metal garbage can lid and keep it filled with water. I used to do that in California and every morning I had quail, western racers, rattlesnakes, kingsnakes, etc.... come to get a drink.

The thing with relocating the snakes is this:

Suitable places to spend the winter is key to supporting a garter snake population. No matter how suitable the habitat, they will need to survive the winter. Cracked foundations, rock walls, rodent burrows which stay dry in winter, anything like that will do. They need to get below ground so they don't freeze, and they need to be safe from getting "flooded out". If you have plenty of worms and slugs in your garden they will probably find enough to eat.

You might want to consider creating an artificial den.