Water flow on the Willie

What do most people consider an acceptable flow rate on the W for springers?  What is considered a safe flow rate to anchor a kayak, being new to kayak fishing, I certainly want to play it very safe at the beginning. I've read some of the past threads on safety and do's and don'ts of anchoring, people talk about don't anchor when the rivers running too fast, is there a rough way to estimate this besides the old "Holy crap, I just lost all my anchor rope"?

Thanks
John