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Geotalk: Claudia Cherubini and the art of characterising aquifers

10 Apr

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

17 Mar

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.

Imaggeo on Mondays: Friends in the field

24 Feb

Out in the field you encounter all sorts of wildlife and while mosquitos are the most frequent (and most unwelcome), they generally don’t interfere with your equipment or your data. The same can’t be said for all animals though, and many scientists have to strap their equipment out of reach, barricade it with barbed fences or place it in a relatively indestructible black box. It’s a particular problem when you need to head back to the lab or lecture theatre, and leave your equipment alone to collect precious scientific data remotely.

Animals can also cause a ruckus when you’re on site – after all, what’s more exciting than a geoscientist and their portable laboratory? This is surely the question that played on the minds of these bovine beasties before interfering with a geoelectrical survey, a method used to monitor CO2 storage and map groundwater.

Does it work? (Credit: Robert Supper, distributed via imaggeo.egu.eu)

Does it work? (Credit: Robert Supper, distributed via imaggeo.egu.eu)

While surveying groundwater in Salzburg, Austria, Robert Supper caught a crowd of curious cows taking a closer look at his equipment. “During the measurements on a meadow, we were inspected by a drove of cows, which immediately started to taste electrodes and cables,” he explains.

“On geoelectrical surveys in rural areas, we often encounter an interesting phenomenon: cows or sheep completely ignore us until we finish the installation of cables and electrodes. As soon as we are ready and want to start the measurements, they start to inspect everything, sniff on the equipment, nibble on the cables, stumble over the profile or (worst case) shit on it. If everything was tested correctly by them, they disappear,” Supper adds. Take care when you’re working in a rural area, you might just get some company.

By Sara Mynott, EGU Communications Officer

If you are pre-registered for the 2014 General Assembly (Vienna, 27 April – 2 May), you can take part in our annual photo competition! Up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at http://imaggeo.egu.eu/photo-contest/information/.

Imaggeo on Mondays: A feast of pancakes

30 Dec

The thought of pancake ice always makes me a little hungry – I just can’t help thinking about stacks of syrup-drowned pancakes, or crepes covered wish sugar and doused with lemon juice – but the science of pancake ice is quite a tempting topic too!

Pancake ice occurs in areas where ice formation is repeatedly disturbed by water movement. In the Southern Ocean, the water extremely open and the swell of the waves causes a large soupy mixture of saltwater and needle-like ice crystals (frazil) to form. This slushy mixture is known as grease ice. Cyclical movement of the slush causes crystals to be compressed and begin to form cakes. Over time, the ice crystals stick together to form thin pancakes that are roughly 30 centimetres to 3 metres in diameter, like these:

Pancake ice in Drake Passage, the Southern Ocean by Kenneth Mankoff. This photo is distributed by the EGU under a Creative Commons licence.

Pancake ice in Drake Passage, the Southern Ocean” by Kenneth Mankoff. This photo is distributed by the EGU under a Creative Commons licence.

This field of ice pancakes in the Southern Ocean is constantly moving as waves cause them to jostle and bump on the water’s surface. The bumping causes the soupy grease ice to be sloshed up onto the edges of each pancake. As the water drains away, a raised lip of ice crystals is left behind – the feature that gives pancake ice its wonderful pancake-like texture.

In the Northern Hemisphere, pancake ice may become more common as the decline in inter-annual sea ice cover frees up larger expanses of water and allows it to swell. Pancake ice isn’t exclusive to the oceans though – it can also form on rivers when temperatures are close to freezing point – enough to form ice crystals, but not so low that the whole river freezes over.

By Sara Mynott, EGU Communications Officer

References:

Linder, C. A.: Sea Ice Glossary. Woods Hole Oceanographic Institution, 2003 (accessed November 2013)

Wadhams, P.: How Does Arctic Sea Ice Form and Decay? NOAA, 2003 (accessed November 2013)

Wilkinson, J. P., DeCarolis, G. Ehlert, I et al.: Ice Tank Experiments Highlight Changes in Sea Ice Types, EOS Transactions, American Geophysical Union, 90, 81-82, 2009

The EGU’s open access geoscience image repository has a new and improved home at http://imaggeo.egu.eu! We’ve redesigned the website to give the database a more modern, image-based layout and have implemented a fully responsive page design. This means the new website adapts to the visitor’s screen size and looks good whether you’re using a smartphone, tablet or laptop.

Photos uploaded to Imaggeo are licensed under Creative Commons, meaning they can be used by scientists, the public, and even the press, provided the original author is credited. Further, you can now choose how you would like to licence your work. Users can also connect to Imaggeo through their social media accounts too! Find out more about the relaunch on the EGU website. 

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