chapter  4
40 Pages

Preferential Flow

I. Classification of Preferential Flow ............................ 124 II. General Features of Preferential Flow ..................... 126

III. Bypassing Flow........................................................... 127 A. Vertical Bypassing Flow...................................... 127 B. Lateral Bypassing Flow ...................................... 129

IV. Fingering Flow ........................................................... 136 A. Criteria for Fingering Flow Generation............. 136 B. Hydrodynamics of Fingering Flow ..................... 137

V. Funneled Flow............................................................ 139 A. Nature of Funneled Flow.................................... 139 B. Experimental Observation.................................. 143 C. Qualitative Features of Funneled Flow ............. 148 D. Modeling Funneled Flow .................................... 150

1. Saturated Funneled Flow Model ................. 150 2. Unsaturated Funneled Flow Model............. 153 3. Further Extension of the Models ................. 156

E. Relation between Theory and Application ......... 158 References............................................................................ 160

I. CLASSIFICATION OF PREFERENTIAL FLOW

It is widely recognized that preferential flows of water in soils have a great effect on hydrological processes in fields. In addition, the role of preferential water flow involving chemicals or contaminations is so important in the environment that many symposia have focused on this topic (1). However, the definition and classification of preferential flow are still under investigation. The classification of preferential flows based on their phenomenological features as proposed by Kung (2,3) is useful. Taking account of his classification, we classify preferential flows in soils into three types: bypassing flow, fingering flow, and funneled flow. Figure 4.1 is a schematic diagram of these flows.