I lived in Austin, Texas, from 1977 to 1979 and regret that I never got involved with Texas river paddling or racing. I was busy with my young career and family and paddled only lakes. But here's an article and video that can give a taste of Texas racing:

Logjams, hallucinations and Mother Nature
Texas Water Safari tests paddlers with grueling 260-mile race from San Marcos to Seadrift
stories.usatodaynetwork.com