Incipient air entrainment due to a free-surface vortex at a horizontal pipe intake passing through a dead-end wall located in a channel is investigated. Available potential flow based methods fail to predict the critical submergence due to friction effects introduced by the dead-end wall. In this study, velocity at the critical spherical sink surface, which is an imaginary spherical surface having identical center and the discharge as the intake, is associated with the average approach flow velocity instead of assuming it as a constant as in the previous studies. This simpler method for determination of critical submergence is tested with available experimental data and the agreement is found to be good. Scale effects are also discussed. It is shown that for the similarity between the model and prototype horizontal intakes in terms of air-entrainment, there is no need to consider Froude, Reynolds, and Weber numbers similarities. (C) 2020 The Author. Published by Elsevier B.V. on behalf of Faculty of Engineering, Ain Shams University.