This post is a question for whoever might be able to help me out.  I was walking along Alameda Creek and I saw various sets of these devices along the levee banks at different locations.  I was curious as to what they could be.  They looked like they would float so I wondered whether they are designed to start at the bottom of the track and then float up as the water levels rises.  Perhaps this then reports back to some control location so everyone knows the level of the creek?  However, that is just a guess.  Does anyone know the real story?