Status and trend of hydrogeological experiments concerning the side-wall flow effect in porous media

Hydrogeological experiments provide an important means to understand groundwater seepage and solute transport problems. Basic hydrogeological parameters can be obtained for use in assessing groundwater resources. In current porous-media research, studies of side-wall flow are in a preliminary and qualitative phase, and lack systematic and comprehensive understanding. Side-wall flow refers to the non-uniform infiltration and solute transport that occurs near the seepage device boundary. Flow dynamics depends on the fluid under the specific hydraulic conditions, physical properties and chemical composition, medium permeability, the roughness of the side wall, geometric features, and physical chemistry. Such phenomena not only occur in indoor water flows and solute transport, but also under natural conditions in the field. Side-wall flow has features both in common as well as distinct from preferential flows. In porous-media experiments, once side-wall flow commences, it affects the groundwater flow field and chemistry field, resulting in parameter values deviating from actual values. Based on a comprehensive analysis of the influence of side-wall flow, a definition of the side-wall flow effect in porous media is given. Three directions of research are identified concerning side-wall flow: the mechanism of the side-wall flows effect, the study of its quantitative impact on seepage flow and solute transport, and the methods and measures that need to be taken in hydrogeological experiments to reduce (or prevent) side-wall flow development.