Is Optimal Waterfall Shutter Speed a Function of Flow Rate?

Wynn Bullock used long exposures in the fourties and fifties to effectively blur ocean scenes. Some of his images make the surf look more like fog than breaking waves and are among my favorite photographs of all time. This was long before Paul Caponegro, who made and continues to make (with the help of Photoshop) great images. I doubt that Bullock was the first person to blur water motion, considering the slow film speeds used in the old days. But perhaps he was one of the first to do so intentionally for artistic effect.

Thank you to all who have answered. I just got back from my week of photographing waterfalls. When I get my slides developed & scanned, I will show you my best results. But this is what I gleaned from earlier posts. Despite my effort to scientifically analyze waterfall shutter speeds, the most enduring comment in my brain last week was the guy (I can't scoll back to find your name, sorry) who said that perhaps my problem was that I had too much water (white space) in my photos. So I backed up and got more background in the photos. I also tried the multiple exposure technique on the most forceful waterfalls, including my favorite waterfall where I used 50mm, 85mm and 85mm + 1.4x converter. And yes, I still think that flow rate has something to do with it, so I found some waterfalls where the flow rate was smaller to get less milked-out areas.

I liked the answers that said that the optimal shutter time varies.

It varies with the velocity of the water, the turbulence of the water, the effect desired by the photographer. It depends on the obstructions and eddies in the water, standing waves, and any other details which might be desireable or undesirable to the photographer's vision of the subject. That said, I also liked the answers where they said Digital. If you can't come back often, I think that a wide time-bracket with a digital camera can show various effects better. Perhaps an additional problem is that I cannot possibly see details on the digital camera that I can see when I download to the PC, so bring a laptop to preview a serious shot! That's my summary of my current opinion, which is, of course, always subject to change.