I am continually amazed at few times fishermen speak of watermanship;which I define loosly as the study of currents in river systems as it relates to fish behaviour and fishing methods and the nature of the river bottom.
The fish rely on this knowledge to define feeding areas,resting areas and migration paths. Moreover our choice of the best lure and fishing method is dependant on this knowledge.
While the overall current speed is determined by the rte of fall of the river channel,it is the roughness of the bottom which creates the difference in speed of the current from the surface to he bottom. Based on the relatively small number of current gradients I have measured in the course of buiding timber bridges and dams It appears that in streams of over four feet in depth surface current may be as much as three times faster than current at the bottom. Indeed if it were not the case it would be impossible for fish to rest comfortably . They are only capable of swimming in waters speeds of more than two miles per hour for relatively short periods. Slots which occur on the eroding bank have in addition to bottom friction ,the slowing effect of bank friction ;thus they often become the prefered migration route of weaker swimming species like Pinks and Chum
This being said I have never encounerted a book on fishing which in my oinion does a thourough job of explaing current patterns . I am still looking for such a book so if you know of one please post a reference. I dont want a textbook on Hydrolics just a fishermans understanding.
coot