The flow behavior in smooth and artificial rough fractures is experimentally investigated. The piezometric head is measured at several positions to determine experimentally the head gradient through a sophisticated procedure, and the hypothesis of one-dimensional flow is verified. It is demonstrated that both the Forchheimer and Izbash equations adequately describe the flow conditions, and proper coefficients for these equations are estimated. The experimental results are also used to construct a Moody-type diagram, where a non-monotonic dependence is shown to characterize the friction factor – Reynolds number relationship in the transition between laminar and weak turbulent flow.