27 research outputs found
Form and function in hillslope hydrology : Characterization of subsurface ow based on response observations
Acknowledgements. We are grateful to Marcel Delock, Lisei Köhn, and Marvin Reich for their support during fieldwork, as well as Markus Morgner and Jean Francois Iffly for technical support, Britta Kattenstroth for hydrometeorological data acquisition and isotope sampling, and Barbara Herbstritt and Begoña Lorente Sistiaga for laboratory work. Laurent Pfister and Jean-Francois Iffly from the Luxembourg Institute of Science and Technology (LIST) are acknowledged for organizing the permissions for the experiments and providing discharge data for Weierbach 1 and Colpach. We also want to thank Frauke K. Barthold and the two anonymous reviewers, whose thorough remarks greatly helped to improve the manuscript. This study is part of DFG-funded CAOS project “From Catchments as Organised Systems to Models based on Dynamic Functional Units” (FOR 1598). The article processing charges for this open-access publication were covered by a Research Centre of the Helmholtz Association.Peer reviewedPublisher PD
High-resolution geophysical surveying at the Springfield Fault, New Zealand
To trace the active Springfield Fault (South Island, New Zealand) and map its character at
shallow depths on a terrace where it exhibits no surface expression, we recorded 3-D georadar
data across an approximately rectangular 110 x 40 m survey area. In addition, we carried out
multi-electrode geoelectric measurements along a 198 m long profile that crossed the
georadar survey area. Although the georadar depth penetration was limited to only ~5 m, the
processed images revealed the presence of a prominent reflecting horizon disrupted by three
main discontinuities. Semi-continuous subhorizontal reflection patterns were interpreted to
represent sedimentary units within the fluvial deposits, whereas three detected discontinuities
were interpreted as fault traces with small near-vertical offsets (~0.4 m). This interpretation
was supported by vertical and lateral changes visible on the final inverted resistivity model
indicating lithological boundaries and fault branches
Practical implications of GPR investigation using 3D data reconstruction and transmission tomography
Non-destructive investigation using ground penetrating radar is becoming
more popular in the inspection of civil structures. Currently, traditional 2D
imaging is used as a preliminary tool to fi nd possible areas of interest for
more detailed inspection, which can be accomplished by more advanced
techniques like 3D image reconstruction or tomography. In this paper,
a general overview of the work done at University of Minho regarding these
techniques is presented, together with their limitations and advantages over
typical radargrams, with implications for civil engineering applications. For
this purpose, data acquisition on two large masonry walls and one large
concrete specimen have been carried out, using refl ection mode, 3D
reconstruction and transmission tomography. The specimens have been
specially built for non-destructive inspection techniques testing, incorporating
different materials and internal voids. Radar tomography and 3D image
reconstruction techniques provided much more detailed information about
structural integrity and shapes and location of the voids, when compared to
2D imaging originally used for potential target identification.Fundação para a Ciência e a Tecnologia (FCT) - POCTI SFRH/BD/6409/2001"Sustainable Bridges" European project - FP6-PLT-0165
HESS Opinions: Functional units: a novel framework to explore the link between spatial organization and hydrological functioning of intermediate scale catchments
This opinion paper proposes a novel framework for exploring how spatial organization alongside
with spatial heterogeneity controls functioning of intermediate scale catchments of organized
complexity. Key idea is that spatial organization in landscapes implies that functioning of
intermediate scale catchments is controlled by a hierarchy of functional units: hillslope scale
lead topologies and embedded elementary functional units (EFUs). We argue that similar soils and
vegetation communities and thus also soil structures "co-developed" within EFUs in an adaptive,
self-organizing manner as they have been exposed to similar flows of energy, water and nutrients
from the past to the present. Class members of the same EFU (class) are thus deemed to belong to
the same ensemble with respect to controls of the energy balance and related vertical flows of
capillary bounded soil water and heat. Class members of superordinate lead topologies are
characterized by the same spatially organized arrangement of EFUs along the gradient driving
lateral flows of free water as well as a similar surface and bedrock topography. We hence
postulate that they belong to the same ensemble with respect to controls on rainfall runoff
transformation and related vertical and lateral fluxes of free water. We expect class members of
these functional units to have a distinct way how their architecture controls the interplay of
state dynamics and integral flows, which is typical for all members of one class but dissimilar
among the classes. This implies that we might infer on the typical dynamic behavior of the most
important classes of EFU and lead topologies in a catchment, by thoroughly characterizing a few
members of each class. A major asset of the proposed framework, which steps beyond the concept of
hydrological response units, is that it can be tested experimentally. In this respect, we reflect
on suitable strategies based on stratified observations drawing from process hydrology, soil
physics, geophysics, ecology and remote sensing which are currently conducted in replicates of
candidate functional units in the Attert basin (Luxembourg), to search for typical and similar
functional and structural characteristics. A second asset of this framework is that it blueprints
a way towards a structurally more adequate model concept for water and energy cycles in
intermediate scale catchments, which balances necessary complexity with falsifiability. This is
because EFU and lead topologies are deemed to mark a hierarchy of "scale breaks" where
simplicity with respect to the energy balance and stream flow generation emerges from spatially organized
process-structure interactions. This offers the opportunity for simplified descriptions of these
processes that are nevertheless physically and thermodynamically consistent. In this respect we
reflect on a candidate model structure that (a) may accommodate distributed observations of states
and especially terrestrial controls on driving gradients to constrain the space of feasible model
structures and (b) allows testing the possible added value of organizing principles to understand
the role of spatial organization from an optimality perspective
A field assessment of the value of steady shape hydraulic tomography for characterization of aquifer heterogeneities
This is the published version. Copyright American Geophysical Union[1] Hydraulic tomography is a promising approach for obtaining information on variations in hydraulic conductivity on the scale of relevance for contaminant transport investigations. This approach involves performing a series of pumping tests in a format similar to tomography. We present a field-scale assessment of hydraulic tomography in a porous aquifer, with an emphasis on the steady shape analysis methodology. The hydraulic conductivity (K) estimates from steady shape and transient analyses of the tomographic data compare well with those from a tracer test and direct-push permeameter tests, providing a field validation of the method. Zonations based on equal-thickness layers and cross-hole radar surveys are used to regularize the inverse problem. The results indicate that the radar surveys provide some useful information regarding the geometry of the K field. The steady shape analysis provides results similar to the transient analysis at a fraction of the computational burden. This study clearly demonstrates the advantages of hydraulic tomography over conventional pumping tests, which provide only large-scale averages, and small-scale hydraulic tests (e.g., slug tests), which cannot assess strata connectivity and may fail to sample the most important pathways or barriers to flow
Enhancing the vertical resolution of surface georadar data
There are far-reaching conceptual similarities between bi-static surface
georadar and post-stack, "zero-offset" seismic reflection data, which
is expressed in largely identical processing flows. One important
difference is, however, that standard deconvolution algorithms routinely
used to enhance the vertical resolution of seismic data are notoriously
problematic or even detrimental to the overall signal quality when
applied to surface georadar data. We have explored various options
for alleviating this problem and have tested them on a geologically
well-constrained surface georadar dataset. Standard stochastic and
direct deterministic deconvolution approaches proved to be largely
unsatisfactory. While least-squares-type deterministic deconvolution
showed some promise, the inherent uncertainties involved in estimating
the source wavelet introduced some artificial "ringiness". In contrast,
we found spectral balancing approaches to be effective, practical
and robust means for enhancing the vertical resolution of surface
georadar data, particularly, but not exclusively, in the uppermost
part of the georadar section, which is notoriously plagued by the
interference of the direct air- and groundwaves. For the data considered
in this study, it can be argued that band-limited spectral blueing
may provide somewhat better results than standard band-limited spectral
whitening, particularly in the uppermost part of the section affected
by the interference of the air- and groundwaves. Interestingly, this
finding is consistent with the fact that the amplitude spectrum resulting
from least-squares-type deterministic deconvolution is characterized
by a systematic enhancement of higher frequencies at the expense
of lower frequencies and hence is blue rather than white. It is also
consistent with increasing evidence that spectral "blueness" is a
seemingly universal, albeit enigmatic, property of the distribution
of reflection coefficients in the Earth. Our results therefore indicate
that spectral balancing techniques in general and spectral blueing
in particular represent simple, yet effective means of enhancing
the vertical resolution of surface georadar data and, in many cases,
could turn out to be a preferable alternative to standard deconvolution
approaches