Not trying to be as harsh as this sounds, but I am a little surpirsed by your suprise. I assume you are a guide, based upon your "client" comment. If you are a guide, then you should have known better than to simply wait for a horn and you should know to never trust a horn, a whistle, or a phone call when it comes to river levels on a tailwater in Arkansas. Always trust your surroundings and your own senses (there is also a pretty reliable phone network of guides on the river when the water comes up). I am glad you got out ok, but you got to keep your eyes, ears, and senses open for the protection and safety of your client when on stream. If something would have happened to your client, it would have been on your hands and not the corp.
All that being said, it happened to me but luky for me it happened to me on my first trip to the White almost a decade ago, and I was out at Wildcat when the water came up. I managed to "river float/hop" back to the access and back my truck out of the river before it came up much further. Since then, i always have an eye on the water conditions.
--Matt Tucker