Induced and Controlled Horizontal Flow in the Vadose Zone

A combination of laboratory experiments and numerical studies were utilized to demonstrate that horizontal flow can be induced and controlled in fine sediment lenses / layers within the vadose zone. Specifically this work demonstrates that through the use of suction-cup lysimeters, water can be injected / withdrawn from continuous zones of fine sediments, bordered by coarse sediments, without inducing significant vertical flux through underlying coarser sediments. The efficacy of this method was demonstrated through controlled laboratory experiments in which horizontal flow and tracer transport was induced in a lens of fine sand imbedded in a matrix of coarse sand. It was demonstrated at a scale of 0.25 meters that the fluid within the fine sand will be displaced (through injection / withdrawal from embedded lysimeters) without inducing vertical flux below the fine-sand lens. These experiments also demonstrated that flow in the fine sand, without vertical migration into the underlying coarse sand, can be maintained over an extended time period (the experiments were run for periods of up to 45 days). Finally, these lab experiments demonstrated that flow could be established in slanted layers, flow moving with and against gravity, as well as in horizontal layers. A numerical model was used, in combination with published moisture retention and relative permeability parameters for a variety of sediment types, to demonstrate that such horizontal flow can be established within different mixtures of sediments and over substantially greater distances (e.g., 10 meters) for select classes of heterogeneity involving lens or layers of finer grained sediments bounded by coarser grained sediments.