I went by the 2009 Riverside nest site to look at the remains of the fallen nest. There was lots of ribbon, what looked like nylon rope pulled apart and an Ace bandage.
The nest built in the same location after the 2008 nest failure also fell down, so this is not bad news. The hawks should be rebuilding the nest in the next few weeks. "Where will they build it?" is the question.
Exiting the park, I got a good look at the restoration project of the biking and walking path along the river in the upper 80's and 90's. It finally looks like they're making progress and that it should be completed soon.