Sorry I'm a bit late on the draw on this one but I just hopped on the forum for the first time in months. It sounds like everyone educated you pretty well on techniques and equipment but I thought I'd give you some info on the places you were asking about.
I've fished Gibbons Creek below the spillway a couple of times. Nothing of size from my experience but I've caught quite a few carp and buffalo in the 3-5 pound range. They haven't released water in ages so the more "desirable" species (catfish, bass, etc) get fished out pretty fast but the carp and buffalo get left behind. Which is fine with me

Similar situation at Lake Bryan. Nothing of size from my experience but fun none the less. I've only caught carp but there are probably buffalo as well. Some of the deepest water you can reach from shore is under the bridge that crosses over where the two sides of the lake connect (google earth can explain it better than I can.)
George Bush Library supposedly has some very nice bass and really large sunfish but I've only ever fished it with lures quickly between classes. Only caught one bass of about 3 pounds. Just be sure to bend back the barbs on your hooks if you go, its a rule.
Gabbard Park is one of the parks thats stocked annually by the city with channel cats. You can realy tear them up with beef liver but don't expect to catch anything over a pound or two. I've heard central park is a better option for larger catfish.
Anyways, I hope this helps! Sorry I found this a little late.