Not sure that it's the brazos below Post but a feeder creek called The Double Mountain fork that feeds Lake Alan Henry. Another feeder goes north of that town. This merges with the salt fork of the Brazos SW of Knox city on it's way to Seymour. All these areas got a lot of rain and those dry arroyos will gush with water after an 8 inch rain. Below Graham, Dry Branch comes in below Hubbard Creek but there's no help from there with that lake 30 feet low (interesting they built a lake on "dry Branch") Same thing for Salt Creek and comes from Lake Graham and Edleman, as they are way low.
Amazing that PK is a huge lake with a river feeding it that drains the West Texas desert.
John 21:3 Simon Peter saith unto them, I go a fishing. They say unto him, We also go with thee.