We took this photo this morning during our walk on the Town Lake trail. Keep in mind, this is the dammed up portion of the Colorado River which forms Town Lake in downtown Austin. Normally you would not even be able to see the current moving. In fact, right out there in those rapids is where you are likely to see the UT rowing teams practicing in their long, slender rowing sculls.
Here is a link to a whole gallery of photos of the flood, including the open flood gates at Mansfield Dam.