Macropore Flow and Its Characteristics

Conventional theories of water flow in soil assume local equilibrium at the elementary volume scale. However, in recent years, this assumption has been abandoned to account for non-equilibrium flow through preferential pathways in soil macropores. Characteristics of macropores such as size, shape, and roughness affect the flow processes through these pores. Various models are available for modelling the flow through these pores; however, they are based on various underlying assumptions. Lately, physics based pore-scale models have been proposed, they cannot be easily upscaled for field applications. Empiricism and parameterization of models again depends upon the application. This chapter focuses on the characteristics of soil macropores and their effect on macropore flow. A comprehensive comparison is established made between the two broad approaches to model macropore flow. We also discuss strategies that can be used to ensure that the models for macropore flow are physically justified and universally acceptable.