Hydromechanics and Kinematics in Preferential FlowGermann, Peter F.Soil Science: January/February 2018 - Volume 183 - Issue 1 - p 1–10 doi: 10.1097/SS.0000000000000226 Invited Article Abstract Author Information ABSTRACT Preferential flow covers macropore flow, nonequilibrium flow, and finger flow that are here exclusively approached with gravity-driven viscous flow. The basic unit is a water content wave whose two parameters are the wave's film thickness and its mainly vertical contact area per unit soil volume. The spatiotemporal wave properties depend on soil structure and on the intensity and duration of water input to the surface. Kinematic wave theory provides the mathematical tool for solving the analytical expressions. Three cases are the basic building blocks for approaching preferential flow: (a) single pulse, (b) a faster pulse trails a slower pulse, and (c) a faster pulse overtakes a slower pulse. Analytical procedures are presented for each case, and the potential of their applications is discussed. The analytical expressions and the superfluous representative elementary volume greatly facilitate preferential flow modeling. University of Bern, Bern, Switzerland. Address for correspondence: Dr. Peter F. Germann, Geographisches Institut der Universität Bern, Hallerstrasse 12, CH-3012 Bern, Switzerland. E-mail: firstname.lastname@example.org Financial Disclosures/Conflicts of Interest: None reported. Received February 15, 2018. Accepted for publication June 7, 2018. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.