American Whitewater - NM State Rivers
look at this page for descriptions and flows....Actually joining American Whitewater is also a good thing to support river conservation. Most rivers, if you click on their line, will have descriptions. AW has flows for the entire country, and international too.
Upper Box= Class V with sieves
Lower Box = Class III-IV
two other books that are invaluable are
Colorado Rivers and Creeks
River Gypsies Guide to North America
And yes that is the correct book you found....If you get just one get WWSR. that is the 'new testament' of guide books for the southwest.