GeoLog

hydrogeology

Imaggeo on Mondays: The Final Effort

We’ve all been there: long hours in the field, a task that seems never ending but which has to be finished today. This week’s Imaggeo on Mondays image is brought to you by Patrick Klenk who highlights the importance of how ‘getting the job done’ relies on good team work!

Two years ago I posted this picture to imaggeo as a tribute to everyone who ever experienced the perils and pitfalls of outdoor field experiments and especially to the colleagues who help you to pull through in the end. It is their scientific spirit which allows to add that indispensable calibration measurement making the difference between a heap of nice-to-look-at data and a quantifiable dataset — even if this means staying on for that extra hour in quickly fading daylight while the cold of a late autumn night encroaches already relentlessly upon your exposed field site.

Final Effort (Credit: Patrick Klenk via imaggeo.egu.eu)

Final Effort (Credit: Patrick Klenk via imaggeo.egu.eu)

In this particular case, we started out on a bright late autumn day, planning to quickly complete a week-long series of Ground-Penetrating Radar  (GPR) experiments on our ASSESS test site in the vicinity of Heidelberg, Germany.  Most certainly, we intended to be finished long before this picture was taken — but alas, as most environmental scientists who are concerned with experimental field studies can probably relate to, outdoor experiments often do not work out exactly as planned and especially timetables get overturned more often than not. In the end, this field day turned out to be the last usable field day for that season and only through the final team effort pictured here we were able to successfully complete a quite involved series of GPR experiments.

The aim of these GPR experiments is to quantify near-surface soil hydraulic properties through the observation of soil water dynamics with non-invasive measurement methods directly at the field scale.  To date, the quantification of soil hydraulic properties remain the holy grail of soil sciences, since they are difficult to determine but widely required for a range of applications such as precision agriculture or the prediction of contaminant flow through the subsurface. Traditional approaches, which determine soil hydraulic properties e.g. from soil samples in the laboratory, suffer from their high cost, their destructive nature and from issues of transferability of the results back to the field. We specifically designed our test-site with a complicated but known subsurface structure to allow for the development of quantitative, high-resolution observations of soil water dynamics with GPR.  In brief, our approach compares GPR observations of soil water dynamics related processes such as: water sprinkling from above the surface (infiltration) or a varying water table depth (achieved by pumping water in and out of the structure from below: imbibition and drainage) to numerical simulations of both subsurface water flow and the expected GPR response. Our research then focuses (i) on observation based estimation methods of the parameters which are needed by the models we use to calculate physical property distributions (inversion) and (ii) on data assimilation methods (i.e. a form of continuously integrating modelled states of a physical system with available observational data) to optimally combine all available information for quantifying the soil properties in question.

 

Patrick is a physicist, currently working as a postdoc with the soil physics group at the Institute of Environmental Physics, Heidelberg University, Germany, on novel approaches for developing Ground-Penetrating radar for quantitative soil hydrology.

 

By Patrick Klenk, postdoctoral researcher at the Institute of Environmental Physics, Heidelberg University, Germany

 

References

Buchner, J.S., Wollschläger U., Roth K. (2012), Inverting surface GPR data using FDTD simulation and automatic detection of reflections to estimate subsurface water content and geometry, Geophysics, 77, H45-H55, doi:10.1190/geo2011-0467.1.

Dagenbach, A., J. S. Buchner, P. Klenk, and K. Roth (2013), Identifying a soil hydraulic parameterisation from on-ground GPR time lapse measurements of a pumping experiment, Hydrol. Earth Syst. Sci., 17(2), 611–618,doi:10.5194/hess-17-611-2013.

Klenk, P., Jaumann, S., and Roth, K. (2014): Current limits for high precision GPR measurements, in ‘Proc. 15th International Conference on Ground Penetrating Radar (GPR2014), 30 June-04 July 2014, Brussels, Belgium, available online shortly.

Klenk, Patrick,  Developing Ground-Penetrating Radar for Quantitative Soil Hydrology, PhD-Thesis, Heidelberg University, 2012, http://www.ub.uni-heidelberg.de/archiv/14329.

 

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

 

 

GeoTalk: Claudia Cherubini and the art of characterising aquifers

This week in GeoTalk, we’re talking to Claudia Cherubini, a research professor from La Salle Beauvais Polytechnic Institute. Claudia shares her work in hydrogeological modelling and delves into how such models can be used in water management…

Could you introduce yourself and tell us a little about what you’re currently working on?

I am an environmental engineer with a PhD in hydrogeology. After more than four years of post-doctoral activity, I finally got a position as associate professor at LaSalle Beauvais Polytechnic Institute, one of the most reputable schools for engineering geologists in France.

My field of research involves characterising flow and transport phenomena in heterogeneous aquifers. My research interests include also advanced geostatistical methods to model complex spatial patterns of contaminants and quantify risk assessment – something I concentrated on when working as a consultant for the Italian Ministry of Environment and the Apulia Region (southeastern Italy).

Meet Claudia! (Credit: Claudia Cherubini)

Meet Claudia! (Credit: Claudia Cherubini)

During EGU 2012, you received a Division Outstanding Young Scientists Award for your work on hydrogeological models and how they can be used in resource management. Could you tell us a bit more about your research in this area?

Before coming to France, most of my research dealt with the hydrogeology of the fractured limestone aquifer in Apulia and, in particular, with water management in coastal aquifers.

The key study concerning this prize is published in Natural Hazards and Earth System Sciences. Together with my Italian colleague Nicola Pastore, I combined two models – one describing density-driven flow and another describing fault hydrogeology – to find out more about the aquifer system in southern Italy. The coupled models let us work out how this complex aquifer could be exploited as well as determine its vulnerability to seawater intrusion. Vulnerability assessments like these are needed for sustainable planning, both in terms of picking well locations and setting pumping rates.

Fractured aquifers are key water sources for many people around the world, how do your findings relate to sustainable water use in these areas? 

Most of my research deals with modeling groundwater flow and contaminant transport in fractured aquifers. Detailed geological reconstructions are used in hydrodynamic modelling to help interpret flow dynamics and the way contaminants are transported. Hydrogeological modelling is extremely important to optimise water extraction in fractured aquifers, to pin down pollution sources or predict the fate of a contaminant. All of these help decide how to manage areas that have been affected by a pollutant. Due to the complexity of fractured rock aquifers, they are often oversimplified. My research aims to apply discrete models to better describe flow and transport dynamics in these aquifers.

How does knowing more about groundwater help scientists understand the impacts of polluted sites on the surrounding environment?

In fractured-rock aquifers, the fracture’s orientation may cause the contaminant plume to be transported in a direction that diverges from the regional hydraulic gradient. Being able to characterise the dominant fractures in the system is extremely useful for aquifer cleanup.

How can hydrogeologists set up something close to what we might find in nature in the lab?

In fracture formations, multiple scales of heterogeneity may exist and there is the need to characterise them at the core, bench and field scale. There is some degree of skepticism about how representative physical models are of phenomena occurring in field conditions though. Laboratory experiments have the advantage of improving our understanding of physical mechanisms under relatively well-controlled conditions, which is not exactly the case in the field.

Key parts of the lab. (Credit: Claudia Cherubini)

Key parts of the lab. (Credit: Claudia Cherubini)

Do you prefer fieldwork or fixing up a laboratory experiment?

I would say probably the second. Dealing with lab experiments concerning fractured media is a matter of creativity and innovation, as there is still a lot to do in this research area.

However, here at LaSalle Beauvais we have set up a hydrogeological platform with an experimental site with 18 boreholes up to 110 m deep, each equipped with piezometers – instruments used to measure liquid pressure, so future directions are oriented towards fieldwork.

What do you enjoy about working in science?

I always felt at ease in science and I have always enjoyed doing research everywhere I go. I currently speak English, German, Spanish, French and obviously Italian (my native language). I spent some research periods abroad: during my PhD at The University of Göttingen Geosciences Centre, and during my post doc at Lawrence Berkeley National Laboratory and at United States Geological Survey in California too.

Finally, what are your research plans for the future?

I work in Picardy (north of France), a region characterised by a fissured chalk aquifer, where the unsaturated zone has been poorly investigated. I am setting up a study with the notable scientist John Nimmo of the USGS, aiming to investigate preferential flow dynamics and their role in recharge within this chalk aquifer.

And I have an Italian PhD student to supervise! She will come here to do laboratory and field experiments on the platform. We also plan to integrate our network into the French H+ observatory, a database for data from a network of highly heterogeneous hydrogeological sites.

Find out more about Claudia’s work on fractured aquifers…

Cherubini, C. and Pastore, N.: Critical stress scenarios for a coastal aquifer in southeastern Italy, Nat. Hazards Earth Syst. Sci., 11, 1381-1393, 2011.

Cherubini, C., Giasi, C. I., and Pastore, N.: On the reliability of analytical models to predict solute transport in a fracture network, Hydrol. Earth Syst. Sci. Discuss., 10, 2013. (currently under open review)

Cherubini, C.: A modeling approach for the study of contamination in a fractured aquifer. Geotechnical and Geological Engineering, 26, 519-533, 2008.

Cherubini, C., Giasi, C. I., Pastore, N.: Evidence of non-darcy flow and non-fickian transport in fractured media at laboratory scale. Hydrol. Earth Syst. Sci., 17, 2599–2611, 2013.

Cherubini, C, Giasi, C. I., and Pastore, N.: Bench scale laboratory tests to analyze non-linear flow in fractured media. Hydrol. Earth Syst. Sci., 16, 2511-2522, 2012.

If you’d like to suggest a scientist for an interview, please contact Sara Mynott.

 

Imaggeo on Mondays: Winter waterfalls reveal their secrets

Cyril Mayaud is kicking of this week’s Imaggeo on Mondays with an insight into what waterfalls in winter can tell us about their local hydrology… 

The picture below shows the lower Peričnik waterfall during winter season. This cascade system is composed of two successive waterfalls that stretch some 16 metres (upper fall) and 52 metres (lower fall) high and is one of the most beautiful natural sights in the Triglav National Park. The cliff is located at the western rim of a U shaped valley and is composed of a very permeable conglomerate rock, which is made up of glacier material that accumulated at the rims of the valley back when the glacier retreated.

Peričnik waterfall from behind the scenes. (Credit: Cyril Mayaud

Peričnik waterfall from behind the scenes. (Credit: Cyril Mayaud

The high permeability of the rock provides an important path for water transfer, letting it infiltrate between the level of the upper and the lower fall. This transfer is particularly visible if you walk in the passage under the fall, where the infiltrated water falls at an intensity comparable to a strong shower. Winter is also a fascinating time to visit the falls and see how the water flows from the upper level to the lower level. The low temperatures freeze the dripping water, creating a picturesque landscape with beautiful ice stalactites and draperies.

Peričnik waterfall, an amazing sight in Slovenia’s Triglav National Park. (Credit: Cyril Mayaud, distributed by imaggeo.egu.eu)

Peričnik waterfall, an amazing sight in Slovenia’s Triglav National Park. (Credit: Cyril Mayaud, distributed by imaggeo.egu.eu)

As hydrogeologist, I see two key scientific points of interest in this picture: the first relates to the water transfer between the two levels, which is delayed during winter (due to the low temperatures) as it shows a spatial snapshot of the infiltration processes through the outcrop. The second underlines the importance of accurately quantifying all the different hydrological processes in a given catchment in order to better understand its hydrological behaviour. As an example, the storage of water as snow is really important for mountainous catchments (like the catchment of the Fraser River in British Columbia) and plays a prominent role in retaining water during the cold season and releasing it during spring/summer.

The waterfall in summer, a wonderful view. (Credit: Cyril Mayaud)

The waterfall in summer, a wonderful view. (Credit: Cyril Mayaud)

A parallel could be also made with the hydrological behaviour of karst aquifers, which depend on a variety of processes, each with different time scales. Because these aquifers contain fractures with a huge size range (from cracks less than 1 mm wide to conduits bigger than 10 metres), these aquifers allow water to infiltrate in two very different ways, and are said to have a double infiltration capacity: rapid and localised infiltration through sinkholes and ponors, and slow, diffuse infiltration of rainwater in the unsaturated zone. The origin and path of the water can normally be differentiated during chemical sampling in the spring.

By Cyril Mayaud, University of Graz  Austria

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.