Periodic Reporting for period 1 - UnsatPorMix (Impact of structural heterogeneity on solute transport and mixing in unsaturated porous media)
Reporting period: 2019-09-01 to 2021-08-31
Water flow and dissolved material transport are common phenomena in the natural environment, specifically in soils, riverbeds, and groundwater reservoirs. These environmental niches generally termed "porous media," are characterized by complex internal structures. These structures are created by the arrangement of solid grains, which form a network of small voids, or pores, between them. The dissolved materials in question can vary significantly in form and characteristics, including dissolved salts, fertilizer, organic and inorganic pollutants, etc. Critical environmental processes depend on the transport of these dissolved materials, including groundwater pollution and the health and fertility of soils.
In many cases, the porous medium conducting the flow - the soil or the sediment - is not saturated with water. In such instances, flow is maintained only through a particular medium part that still conducts water. We find this type of unsaturated water flow in soils and the unsaturated zone located beneath the soil and above the groundwater level. The distribution of water in an unsaturated porous medium can vary significantly with the internal structure of the medium. It is also known (but not entirely understood) that the connectivity and form of the water-conducting part of the medium significantly impact solute transport processes.
The overall objective of UnsatPorMix is, therefore, to improve our understanding of the connection between porous medium structure and the transport of solutes under unsaturated flow conditions. We will initially approach this topic experimentally by developing an experimental system that will allow the acquisition of high-resolution images of solute transport in unsaturated transparent porous medium samples. Different structures will characterize the samples, and we will compare saturated and unsaturated flow conditions. The results of the experiments will provide new insight into the fundamental mechanisms controlling solute transport in the natural environment. The experimental results will be the basis for developing improved models that will allow us to predict the behavior of solutes in the environment.
In many cases, the porous medium conducting the flow - the soil or the sediment - is not saturated with water. In such instances, flow is maintained only through a particular medium part that still conducts water. We find this type of unsaturated water flow in soils and the unsaturated zone located beneath the soil and above the groundwater level. The distribution of water in an unsaturated porous medium can vary significantly with the internal structure of the medium. It is also known (but not entirely understood) that the connectivity and form of the water-conducting part of the medium significantly impact solute transport processes.
The overall objective of UnsatPorMix is, therefore, to improve our understanding of the connection between porous medium structure and the transport of solutes under unsaturated flow conditions. We will initially approach this topic experimentally by developing an experimental system that will allow the acquisition of high-resolution images of solute transport in unsaturated transparent porous medium samples. Different structures will characterize the samples, and we will compare saturated and unsaturated flow conditions. The results of the experiments will provide new insight into the fundamental mechanisms controlling solute transport in the natural environment. The experimental results will be the basis for developing improved models that will allow us to predict the behavior of solutes in the environment.
We have developed a novel experimental setup with three main characteristics:
1. A transparent synthetic porous medium model that allows direct imaging (by high-resolution cameras) of the flow of water and colored solutes.
2. The ability to create unsaturated flow conditions in the porous medium model by injecting air in a unique system.
3. Our system allows us to change the porous medium model itself and test different structures.
Preliminary experiments show promising results and demonstrate our system's capability of capturing complex flow phenomena and solute transport. These results are in agreement with previously published experimental work. Thus, they allow us to take the next step in our experiments towards using porous medium models with different internal structures.
1. A transparent synthetic porous medium model that allows direct imaging (by high-resolution cameras) of the flow of water and colored solutes.
2. The ability to create unsaturated flow conditions in the porous medium model by injecting air in a unique system.
3. Our system allows us to change the porous medium model itself and test different structures.
Preliminary experiments show promising results and demonstrate our system's capability of capturing complex flow phenomena and solute transport. These results are in agreement with previously published experimental work. Thus, they allow us to take the next step in our experiments towards using porous medium models with different internal structures.
The expected results will show how the flow conducting medium's structure impacts solute transport processes. This is still not well known and hardly understood. The data we will acquire with our experiments would facilitate future model development to advance state-of-the-art further. The unique system we are developing and the data we will acquire will also help establish collaborations with other researchers interested in related topics, such as microbial activity in the soil or nutrient uptake by plant roots.