Scales and dimensions of momentum dissipation during preferential flow in soils

Momentum dissipation may dominate flow in soils over a considerable distance when input rate and antecedent soil moisture are high enough and when adequate soil structures are present. The concept is derived from momentum balance. It is applied to drainage flow from a column of undisturbed soil and a weighing lysimeter and to water content variations at five depths due to sprinkling. Momentum of input is much lower than momentum during flow in the soil; however, the former is considered important in triggering momentum dissipation within the profile. Drainage flow at a depth of 2.2 m shows flow completely dominated by momentum dissipation, whereas momentum of flow within the soil profile increases with depth, indicating acceleration over a vertical distance from 0.15 to 0.55 m. The Reynolds numbers show laminar flow in all cases.