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118 CHAPTER 3. TERRESTRIAL SYSTEMS
Background
Transport of water, dissolved chemicals, and heat are intimately linked in soils and they are an important
aspect of many environmental issues like quantity and quality of groundwater, irrigation and
soil salinization, coupling of soil and atmosphere, and stability of permafrost soils. Major challenges
are (i) the understanding of the physical basis of these highly nonlinear processes and (ii) the quantitative
understanding of their manifestation at the scale of eventual interest. While the fundamental
understanding typically refers to spatial scales of millimeters to meters, the scale of interest ranges
from hundreds of meters, e.g., for optimized irrigation, to tens or hundreds of kilometers, e.g., for the
impact of landuse changes on climate.
Research Focus
Our primary focus lies on understanding the physical basis of transport processes in soils, specifically
the movement of water, of non-reactive solutes, and of thermal energy. We cover the range from
detailed studies in the laboratory to monitoring at the field scale and from conceptual modeling to
numerical simulation.
A secondary focus is the development of novel approaches to (i) exploring subsurface structures
and (ii) non-invasive measurements of state variables and material properties. Both are prerequisites
for simulating large systems with time scales beyond reasonable experimentation and for monitoring
transport processes.
Project Clusters and Links
Cluster A: Transport Processes
At the lab scale, we study fundamentals of transport in porous media, currently water movement
in coarse-textured media which may become unstable and lead to so-called flow fingers. These have
been shown to be inconsistent with Richards’ equation which underlies most current models of water
movement in soils. We study these instabilities in Hele-Shaw cells. Water saturation and dye
distributions are determined by light transmission (project 3.1.3) which was previously calibrated by
X-ray transmission (project 3.1.2). To improve the quality beyond that achieved with the white light
transmission measurements, we look, with support from the image analysis group of Prof. Dr. Bernd
Jähne, into near-infrared measurements within the absorption bands of water (project 3.1.4).
Concurrent with our experimental studies, Sreejith Kuttanikkad in the parallel computing group
of Prof. Dr. Peter Bastian at IWR develops a high-resolution solver for Stokes’ equation at the pore
scale.
At the small field scale, we investigate the impact of soil structures on water and solute movement.
Of particular importance here are macropores – cracks and wormholes – which may lead to
the bypassing of the biologically active layers. This has an impact on the availability of water for
plants and on the decay of contaminants. An experimental study of so-called preferential flow was
performed in cooperation with INRA at Orleans, Frankreich (Dr. Isabelle Cousin) (project 3.1.7) and
successfully simulated numerically (project 3.1.8).
At the large field scale, we operate test and monitoring sites at Grenzhof, Heidelberg, and near
Ny-˚Alesund, Svalbard. Further sites are planned on the Qinghai-Tibet plateau, China.
The Grenzhof site, located a few kilometers from Heidelberg, is dedicated to exploring transport
processes in natural soils, eventually also the coupling between soil and atmosphere, and to developing
and testing new measuring methods and instruments. Its primary advantages are easy access and
vicinity to the institute.
The site is 20 m × 10 m in size. It is equipped with an automated weather station (air temperature,
humidity, and pressure, wind speed and direction, precipitation, radiation components), a profile of
ground temperature sensors down to 1.6 m, and two profiles of time-domain reflectometry (TDR)
probes for measuring liquid water content down to 1.4 m.
During the installation of the ground instruments, large soil cores where extracted whose hydraulic
properties are measured in the lab as described below on “Inverse Determination of Soil Hydraulic
Properties”.
Weekly measurements with ground-penetrating radar (GPR) yield novel information on the dynamics
of soil water content at the field scale which is compared with the point measurements provided
by TDR (project 3.1.9).