Looks like a sedge rather than a reed.

Texas has 94 Carex species. It might help to get another photo, of the seed heads, after the flowering is finished. It would also help if you photographed samples of the flowers and foliage with a white paper background. A few candidates are C. albican, C. alma, C. crus-corvi, C. emorii, C. occidentalis, C. typhina, C. verrucosa. I didn't check species height.

If you can just single out one stem like these pictures, you don't have to have a white paper background.

Well, 3 stems here, but they aren't in a big tangle. This Carex above looks similar to your's but Carex senta doesn't grow in Texas, supposedly.

It helps to see the seedhead like this, after flowering.