34 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 Kƶhn, 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 BegoƱa 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 āFrom Catchments as Organised Systems to Models based on Dynamic Functional Unitsā (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
Form and function in hillslope hydrology : in situ imaging and characterization of flow-relevant structures
Thanks to Elly Karle and the Engler-BunteInstitute, KIT, for the IC measurements of bromide. We are grateful to Selina Baldauf, Marcel Delock, Razije Fiden, Barbara Herbstritt, Lisei Kƶhn, Jonas Lanz, Francois Nyobeu, Marvin Reich and Begona Lorente Sistiaga for their support in the lab and during fieldwork, as well as Markus Morgner and Jean Francois Iffly for technical support and Britta Kattenstroth for hydrometeorological data acquisition. Laurent Pfister and Jean-Francois Iffly from the Luxembourg Institute of Science and Technology (LIST) are acknowledged for organizing the permissions for the experiments. Moreover, we thank Markus Weiler (University of Freiburg) for his strong support during the planning of the hillslope experiment and the preparation of the manuscript. This study is part of the DFG-funded CAOS project āFrom Catchments as Organised Systems to Models based on Dynamic Functional Unitsā (FOR 1598). The manuscript was substantially improved based on the critical and constructive comments of the anonymous reviewers, Christian Stamm and Alexander Zimmermann, and the editor Ross Woods during the open review process, which is highly appreciated.Peer reviewedPublisher PD
Investigating the Stratigraphy of an Alluvial Aquifer Using Crosswell Seismic Traveltime Tomography
In this study, we investigate the use of crosswell P-wave seismic tomography to obtain spatially extensive information about subsurface sedimentary architecture and heterogeneity in alluvial aquifers. Our field site was a research wellfield in an unconfined aquifer near Boise, Idaho. The aquifer consists of a ~ 20-m-thick sequence of alluvial cobble- and-sand deposits, which have been subdivided into five stratigraphic units based on neutron porosity logs, grainsize analysis, and radar reflection data. We collected crosswell and borehole-to-surface seismic data in wells 17.1 m apart. We carefully considered the impact of well deviation, data quality control, and the choice of inversion parameters. Our linearized inverse routine had a curved-ray forward model and used different grids for forward modeling and inversion. An analysis of the model covariance and resolution matrices showed that the velocity models had an uncertainty of \u3c10 m\u3e/s, a vertical resolution of ~ 1 m, and a horizontal resolution of ~ 5 m. The velocity in the saturated zone varied between 2100 m/s and 2700 m/s. Inclusion of the borehole-to-surface data eliminated the Xshaped pattern that is a common artifact in crosswell tomography, and the increased angular coverage also improved the accuracy of the model near the top of the tomogram. The final velocity model is consistent with previous stratigraphic analyses of the site, although the locations of some of the unit boundaries differ by as much as 2 m in places. The results of this study demonstrate that seismic tomography can be used to image the sedimentary architecture of unconsolidated alluvial aquifers, even when the lithologic contrasts between units are subtle
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.FundaĆ§Ć£o para a CiĆŖncia 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