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Preferential flow in soils is thought to be dominated by the dissipation of momentum. The strict application of momentum dissipation to flow in macroporous soils leads to a kinematic wave approach. The basics are summarized and calibration procedures are introduced. The approach represents well drainage flow and soil moisture variations, measured with either horizontally or vertically installed TDR-wave guides. Rates of preferential flow can be estimated from soil moisture readings. The approach yields mobile soil moisture, its total contact length with the parts at rest and its average film thickness, thus providing for information on the geometry of flow and the flow paths. The depth range to which the approach applies, to either drainage flow or soil moisture data, is viewed as measure for the vertical extent of hydraulically functional macropores. The effects of soil compaction on structural pores can thus be demonstrated.