of the obvious.....(usgs)
For a homemade gauge, you will have to get creative. But don't worry....there are
ways. The easiest and fastest is to set up a webcam. These are "cheap"
and effective. Of course you are going to need a resident who is stream side, an internet connection and some sort of water/weather-proofing. This is all fairly simple for the motivated. With the webcam set up, live feed (streaming of course).....you will have to have some sort of reference for a good flow. I.E. a NATURAL rock or stick gauge.
One request..don't spray paint....and when you set it up, give me the link
one example of a homemade "rivercam" is here