The along-hole variation of Darcy friction factor f is usually not exceeding 2-3 % and in many practical applications can be considered as constant along hole f = f_s = \rm const.
The absolute value is staying between f = 0.04 for the very small flow rates (< 100 cmd) and f = 0.015 for the very high flow rates (> 1,000 cmd).
See also
Physics / Fluid Dynamics / Pipe Flow Dynamics / Darcy–Weisbach equation / Darcy friction factor