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The design of water pollution control practices such as vegetative filter strips and riparian buffers typically focuses on surface runoff with subsurface flow and transport usually assumed to be negligible. Field evidence suggests a prevalence of preferential flow in riparian areas due to increase biological activities (roots, worms, etc.) and large hydraulic gradients from adjacent streams. Since subsurface transport of contaminants can be significant with preferential flow, the prevalence of macropores in riparian buffers can negate the intended benefits of this widely-adopted control practice. To limit degradation of aquatic ecosystem services, we review different approaches to simulate macropore flow and transport through the riparian vadose zone. In addition, and due to the especial characteristics of these areas, we also account for the influence that a seasonal shallow water table will have on the subsurface and overland flow and transport processes. The objective of this work is to identify those theories describing macropore flow that may be applied in the riparian buffer scales. Critical need is to characterize the morphology of macropore networks in the field. Yet, we find that this relationship between micro-, meso-, and macro- scale is still deficient and must be further explored. It is anticipated that the holistic knowledge of hydrodynamics through riparian vadose zone can benefit from this work. This understanding provides foundational knowledge towards the improvement of prediction of riparian buffers performance. |
