Watering became trouble because the soil got wet and the tunnels would sink. Not all yards do that. Mine is made of alot of sand instead of good soil. I have no clue what the bugger has done with my compost rich soil. I bet if I went out to the field behind the apartment, I'd find a nice hole full of compost-like soil.
Gophers eat roots, bulbs, grass, tubers, and seeds.
They even harm trees, bushes, vines, and flowers. For me, it was the green bean plants barely a foot tall. They must not like tomatoes because I had no damage to them. Fencing your garden in with the fence going down about 3 feet will generally deter them from your garden. Try fumigating the tunnels with ammonia or sulfur.