There is an account of W.B Witt and others drowning on Page 20-21 at:

http://books.google.com/books?id=ALxyZpd3sScC&pg=PA20&vq=matagorda&source=gbs_search_r&cad=1_1&sig=53VGj7S5zEHH7mb3kOygH3MS8DA

You may find this of interest:
http://books.google.com/books?id=2VkBAAAAYAAJ&lpg=PA121&pg=PA121&ci=75,1089,822,356&source=bookclip#PPA121,M1

There is a regimental history at http://civilwarindiana.com/reg_history_inf0.html