I just spent on short (2 1/2 hr) session under the I-10 bridge one time, last summer, and blanked.
There was some old guy setting jugs for catfish up river a bit, and it did look pretty fishy; no rolling carp though.
The trouble with the lower Brazos, as I can see, is the lack of access. The San Jac has better access.
I'd like to try the Trinity some time as well, but will run up against the access issue again, I'm sure.