Trying to guess when the river will be up or fining down is very difficult though, and even when you think you know a river, some local "variation" can kick in. This is especially the case if you are fishing a river that is quite long and managed (weirs, lock etc).
Also on some river catchments you get two peaks, where the initial surge is followed by a second peak where water enters through underground means as opposed to overland flow...
........and that can depend on time of year (if the river is flanked by agricultural land for example, the season you are in can make a difference), type of local soil and bedrock, previous weather etc etc.
Having spent countless days freezing my nuts off in many rivers in the UK doing hand measured analysis we came to the blinding conclusion that every river was different /forum/smilies/smile_smiley.gif. You just have to get to know your river.
The best thing to do though, if relatively local and you have decided not to fish 'cos it may be steamimg through, is go and see the river a day or two after. That way you get to know it better.