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Water Underground

Water Underground has a new home on the EGU Network Blogs

Water Underground has a new home on the EGU Network Blogs

The newest addition to the Network Blogs is a groundwater nerd blog written by a global collective of hydrogeologic researchers for water resource professionals, academics and anyone interested in groundwater, research, teaching and supervision.

Water Underground was started, and is currently led, by Tom Gleeson. It is the first blog to be jointly hosted by the EGU Blogs and the AGU blogosphere.

Why not take a look at some the past posts to get a feel for what is to come on the new EGU/AGU blog? You can read about what stalagmites can teach us about past and present climate and what scientists mean by crustal permeability. The advances in groundwater research also feature on the blog. Posts on supervision and teaching will be of interest to Earth scientists at all stages of their career too.

Posts in the blog are contributed by a collective of hydrology experts and reviewed by one of the frequent contributors to help improve style and clarity. Tom, and the contributing authors, want to foster a lively community via the blog, so discussion as well as comments on posts is encouraged. Not only that, if you have something to share, be sure to contact the editorial team as submissions are always welcome! Simply drop them a line at: waterundergroundblog@gmail.com

Here at EGU we are thrilled to have Water Underground join our diverse community of geoscience bloggers. Please join us in welcoming Water Underground to the Network Blogs!

By Laura Roberts,  EGU Communications  Officer

The great American groundwater road trip: Interstate 80 over the Ogallala Aquifer

The great American groundwater road trip: Interstate 80 over the Ogallala Aquifer

 


Authored by: Sam Zipper – Postdoctoral Researcher in the Department of Civil & Environmental Engineering at the University of Wisconsin-Madison


In late July, my wife and I loaded the dog into the car, cranked up the water-related tunes, and drove over a few million cubic meters of water. No, we haven’t traded in our sedan for an amphibious vehicle – rather, we were driving west, across Nebraska, on the Interstate 80 highway. While this may be a relatively boring road trip by conventional standards, it does provide an opportunity to drive across the famous Ogallala Aquifer, a part of the High Plains Aquifer system.

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The wide reaching Ogallala Aquifer 1. The red line shows Interstate 80’s route.

While the geological history of the Ogallala is described in more detail elsewhere; the short version is that sediment, eroded off the Rocky Mountains over many millions of years, filled in ancient river channels, eventually creating the flat plains that characterize much of Nebraska today. Despite the flat landscape, however, the sights you’ll see along I-80 exist in their present form almost entirely due to this vast underground supply of water.


Irrigation

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A center-pivot irrigation sprinkler. A common sight over the Ogallala 2.

It’s estimated that upwards of 90% of the water withdrawn from the Ogallala is used for agricultural irrigation. Driving through western Nebraska, 90% seems like an underestimate. Center-pivot systems stretch away from the interstate as far as the eye can see, and it’s hard to imagine what this landscape would look like without the water from the Ogallala. While groundwater levels have declined in the most heavily irrigated parts of Nebraska compared to predevelopment conditions, they’ve fortunately stabilized over the past ~30 years; the most serious drawdowns are occurring further south, in Western Kansas, Oklahoma, and the Texas Panhandle.


The Mighty Platte

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The mighty Platte River. Photo by Sam Zipper.

The Platte River stretches from the Rockies to its confluence with the Missouri River in eastern Nebraska, and I-80 follows the Platte through most of Nebraska. Along the way, the Platte is receiving water from surrounding groundwater systems.  This process of groundwater discharge to streams (often called baseflow), is particularly important for sustaining flow in the river during dry periods, along with the ecosystems, agriculture, and municipalities that depend on this water supply. For a more beautiful look at the Platte than my cell phone camera offers, check out the Platte Basin Timelapse project, which uses photography to explore the movement of water through the basin.


The Namesake

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Ogallala Nature Park welcome sign. Photo by Sam Zipper.

The Ogallala is named after Ogallala, NE, a tiny town about a half hour’s drive from the Colorado border. The aquifer is named after Ogallala because that’s where the geologic “type locality” is – a fancy way of saying, they found the Ogallala formation here first. While we didn’t venture into the town of Ogallala itself, we did stop at the lovely Ogallala Nature Park just off the interstate for a stroll among the phreatophytic vegetation lining the banks of the Platte. Phreatophytes, such as the cottonwoods common to Nebraska, have evolved to have special roots which can extract water directly from groundwater when soil moisture supplies are low, thus allowing them to survive in the sandy, well-drained banks of the Platte.

Do you have any hydrogeologic highlights we should investigate on our drive back to Madison? Let me know via the comments below!


Picture Sources

https://upload.wikimedia.org/wikipedia/commons/thumb/4/44/Ogallala_saturated_thickness_1997-sattk97-v2.svg/2000px-Ogallala_saturated_thickness_1997-sattk97-v2.svg.png

http://water.usgs.gov/edu/pictures/full-size/irrigation-sprinkler-large.jpg


About the author:

Sam Zipper‘s research interests lie broadly at the intersection of humans and the environment, focusing on feedbacks between subsurface hydrology, vegetation dynamics, soil water retention characteristics, and climate & land use change that cut across the disciplines of hydrology and hydrogeology, soil science, agronomy, and ecology.  He is an ecohydrologist at the University of Wisconsin-Madison.

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FloPy: A Python interface for MODFLOW that kicks tail!

FloPy: A Python interface for MODFLOW that kicks tail!

Authored by: Kevin Befus – Assistant professor, Department of Civil and Architectural Engineering at the University of Wyoming


Groundwater modeling is getting better. Models are becoming more sophisticated with simpler interfaces to add, extract, and process the data. So, at first appearances, the U.S. Geological Survey’s (USGS) recent release of a Python module named FloPy for preparing, running, and managing MODFLOW groundwater models seems to be a step backwards.

Oh, but it isn’t.

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First, a couple disclaimers. Yes, at the time of writing this I work for the USGS and use this new Python module for my research. Did I have to use FloPy? No. Am I glad I did? YES! Before using FloPy, I dabbled in the various non-commercial MODFLOW interfaces but got bogged down on how many drop down menus, pop-up menus, wizards, and separate plotting programs with their own menus were needed to make a meaningful groundwater model on top of a new lexicon of variable names (IUPWCB must mean “internally unknown parameter with concentrated bacon”, right?).

FloPy made its official debut in February 2016 with a Groundwater methods report 1. Bakker et al. do an excellent job telling us why we should use FloPy. I’ll leave that to you and tell you what I think.

Here’s what is great about FloPy:

  1. FloPy is 100% MODFLOW. No tweaks to anything. You choose the executable file you want it to use or compile it yourself, and you’re off!
  2. You have the near-infinite data management, manipulation, and plotting capabilities of Python at your fingertips. Python has a lot of packages. It can be overwhelming. You can rely commercial packages like ESRI’s arcpy if you want, but there’s a list of free libraries that give you even more freedom to get the input data just right. Since I mentioned freedom, here’s the list of free libraries I find useful but it is in no way an endorsement nor exhaustive: scipy, numpy, gdal, osgeo, fiona, shapely, cartopy, pyshp, pandas, matplotlib, and let’s not forget…flopy!
  3. It’s easy to duplicate and alter an existing model. Once you have your script perfect for running a particular groundwater model, you can take pieces of it to make a slightly altered version, or you can pop it in a loop that runs through your uncertain inputs for sensitivity testing. Change your grid with the flip of a variable, and make sure that mesh converges!
  4. Loading other MODFLOW models works great. Say you want to run someone else’s model with slightly different recharge, but their recharge is variable in space. Since FloPy incorporates numpy’s grid/matrix handling capabilities, you can change individual entries with row-column selections or change the whole recharge grid by multiplying it by either a single number or say a random matrix with a normal distribution and some added noise. If you just want to use their recharge data to run your own model, you can save the position coordinates (they have hopefully provided you with their coordinate system and model transformations) and recharge arrays to your very favorite format (csv, nc, mat, tif) and load it later as a matrix to add to your model, all in a single Python script.
  5. Building off of the ability to load or create MODFLOW models, FloPy has functions for plotting 2D map or cross-section views of the model discretization, boundary conditions, and results. Shapefiles can be included in these plots if they are in the same coordinate system as the model or extracted from the model (ever want a polygon feature of every model cell with attributes for every property of that cell?). I do my own shapefile manipulations in Python, but FloPy has some great plotting tools built in.
  6. You already have the data in Python. See what adding a low permeability layer does to spring discharge. Then, with the model made, you have to make sense of it. Maybe develop some interesting spatial or time series analyses. Enter Python. Plotting with matplotlib also makes beautiful, journal article-worthy figures…with enough sweat and tears from your end (not as many as you may think). Yes, this is a repeat of 2), but, seriously, it’s in PYTHON!
  7. FloPy is totally free. Python is free. Tons of science-oriented libraries in Python are free.

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Here’s a flashy example.  It is straightforward and only takes one script to create a SEAWAT model from scratch and plot the 2D steady state salinity distribution and flow vectors for a simple Henry 2 problem based on a slightly edited FloPy example script.  There are more than a dozen example scripts available on the FloPy site as well as a very cool capture ratio script provided in the methods report 1.

For the groundwater educators out there, a FloPy groundwater model script can be paired with homework questions that get students testing how changing hydraulic conductivity in certain parts of the model changes the water table configuration. Or maybe a new well needs to be drilled on a plot of land near a spring… The scenarios are endless. Students can develop a fundamental understanding of groundwater flow while getting experience with both groundwater modeling and computer programming. Win, win, and win.

Essentially all of the standard MODFLOW packages are operational in FloPy, and there are varying levels of support for some of the specialized MODFLOW compilations and processing tools (e.g., MODFLOW-USG, MODFLOW-NWT, MT3DMS, SEAWAT, PEST, and MODPATH). PEST and MODPATH are currently not executable with FloPy, but these features will probably be added in a future release (I have made my own klugy modules for running ZoneBudget and MODPATH that interface reasonably well with the rest of FloPy).

Get on your way and give FloPy a try today!


Links

The Python package is available online at https://github.com/modflowpy/flopy.

The documentation is available online at http://modflowpy.github.io/flopydoc/index.html.

The USGS FloPy page is http://water.usgs.gov/ogw/flopy/.


References

Bakker, M., V. Post, C. D. Langevin, J. D. Hughes, J. T. White, J. J. Starn, and M. N. Fienen (2016), Scripting MODFLOW Model Development Using Python and FloPy, Groundwater, doi:10.1111/gwat.12413.

Henry, H.R., 1964. Effects of dispersion on salt encroachment in coastal aquifers. In: Cooper, H.H. (Ed.), Sea Water in Coastal Aquifers: U.S. Geological Survey Water- Supply Paper 1613-C p. C71–C84.


About the author:

Kevin Befus is a groundwater hydrologist with geology and geophysics experience — examining geological, biological, and chemical processes, especially considering their connections to water across scales.

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What caves can teach us about climate, past and present

What caves can teach us about climate, past and present

Authored by:

Gabriel C Rau, Associate Lecturer in Groundwater Hydrology at UNSW, Australia

Andy Baker, Director of the Connected Waters Initiative Research Centre at UNSW, Australia

Mark Cuthbert, Research Fellow in Hydrogeology at the University of Birmingham, UK

Martin Sogaard Andersen, Senior Lecturer at UNSW, Australia


Have you ever enjoyed the cool refuge that an underground cave offers from a hot summer’s day? Or perhaps you have experienced the soothing warmth when entering a cave during winter?

When descending into a cave, you may not only enjoy the calm climate, you may also admire the beauty of cave deposits such as stalagmites, stalactites and flowstones, known by cave researchers as speleothems.

Perhaps you already know that they grow very slowly from minerals in the water that drips off or over them. This water originates from rain at the surface that has travelled through soil and limestone above, and seeped into the ground and ended up in the cave.

As speleothems grow, they lock into their minerals the chemical signatures of the environmental and climatic conditions of the time the rainwater fell at the surface. So, as a stalagmite grows, the surface climate signature is continuously trapped in the newly created layers.

Some very old stalagmites hold climatic signatures of the very distant past, in some cases up to millions of years. They contain an archive of the past climate as long as their age, often predating global weather station records.

Installation of high-resolution temperature sensors inside the cave.

Above and below

But if a cave remains cool during summer and warm during winter, how is its climate related to that of the surface? And how does this affect the chemical signature recorded by speleothems?

To understand the relationship between surface and cave climate, our research group, Connected Waters Initiative Research Centre at UNSW Australia, conducted multiple field experiments at the Wellington Caves Reserve in New South Wales.

During the experiments, the surface and the cave climates were measured in detail. For example, highly accurate temperature sensors were used to measure the water temperature at the surface, and at the point where water droplets hit the cave floor forming stalagmites.

The research team initiated controlled dripping in the cave by irrigating the surface above the cave with water that was cooled to freezing point to simulate rainfall.

The cold water allowed us to determine whether the drip water in the cave is affected by the conditions at the surface or those along its pathways through the ground.

We also added a natural chemical to the irrigation water, which allowed us to distinguish whether the water in the cave originated from the irrigation or whether it was water already present in the subsurface.

Our results revealed a complex but systematic relationship between the surface and the cave climate. For example, surface temperature changes are significantly reduced and delayed with depth.

Our research illustrates how to decipher the surface temperature from that in the cave. Understanding this is necessary to correctly decoding past surface temperature records from their signatures preserved in stalagmites.

Keeping it cool

We also discovered that air moving in and out of the cave can cool cave deposits by evaporating water flowing on the cave deposits. This cooling can significantly influence the chemical signature trapped in the cave deposit and create “false” signals that are not representative of the surface climate.

In other words, it will make the surface climate “look” cooler than it actually was, if not accounted for. While this is more likely to occur in caves that are located in dry environments, it may also have to be considered for stalagmites in caves that were exposed to drier climates in the distant past.

Temperature loggers installed on stalactites to measure the drip water temperature.

Our new knowledge can also help scientists select the best location and type of stalagmite for the reconstruction of past climatic or environmental conditions.

This new discovery is significant because it can improve the accuracy of past climate signals from cave deposits. It may also help us understand previously unexplained artefacts in existing past climate records. By improving our understanding of the past climate we can better understand future climate variations.

Protecting springs from groundwater extraction: is a ‘drawdown trigger’ a sensible strategy?

Protecting springs from groundwater extraction: is a ‘drawdown trigger’ a sensible strategy?

By Matthew Currell – Senior Lecturer at RMIT University

Springs, some of which have been flowing for hundreds of thousands of years, have been disappearing in Australia due to human water use over the past century. Following a hotly contested court case, Australia’s Environment Minister imposed a 20cm ‘drawdown limit’ at a set of springs, to protect them from a proposed coal mine. However, this ignores a fundamental principle of hydrogeology, known as ‘capture of discharge’ and as a result, the springs may still be under threat.

Why are springs important?

Springs are a groundwater system’s gift to the surface.  They provide a constant source of water to the landscape throughout the year, and many have been doing so for millenia. This is why they are often of great importance to indigenous people and why they play an important part in the history of human settlements. Springs also provide valuable ecological refuges in dry landscapes and are often home to endemic species. However, springs are vulnerable to the effects of groundwater extraction.

The disappearing springs of the Great Artesian Basin

Recently, a group of Australian ecologists and hydrogeologists published a study of ‘lost springs’ that have disappeared from the Australian landscape since European settlers began drilling for water and minerals in the Great Artesian Basin (GAB) – the world’s largest artesian aquifer system (the term ‘artesian’ means that when a wellbore intersects one of the aquifers, groundwater flows freely to the surface, often gushing meters up into the air). Groundwater in the Great Artesian Basin travels many hundreds of kilometres across the Australian continent, before surfacing as clusters of springs, which provide life in otherwise dry landscapes (Figure 1). Research by colleagues of mine estimates that some of these springs have been discharging water (at variable rates) for hundreds of thousands of years.  This is based on dating the minerals that have been continuously precipitating at the spring outlets over geologic time. The drilling of wells in the Great Artesian Basin began in the late 1800s and was encouraged by governments, as a way to ‘open up the landscape’ for further white settlement into the country’s harsh, arid interior. Many of these artesian bores were allowed to flow freely for decades (some are still uncapped), leading to major declines in groundwater pressures throughout the Great Artesian Basin. Sadly, this has also caused many springs to disappear.

Great_Artesian_Basin

Figure 1 – Map of Australia’s Great Artesian Basin, which covers four states, showing the major areas of groundwater recharge and discharge, where springs emerge at the surface.  Source: ABC Science: http://www.abc.net.au/science/articles/2012/04/04/3470245.htm

Recent threats to springs from mining

More recently, another human activity threatens springs – mining. In particular, parts of Australia have recently experienced a boom in coal seam gas and large coal mining proposals. Large volumes of groundwater must be pumped from the aquifers above and adjacent to the coal and gas deposits to allow them to be mined. Extracting groundwater for mining means that some water that could otherwise reach the surface at springs is re-directed towards the gas wells or mine pits.  Figure 2 shows a map of oil and gas exploration and production permits that currently cover the Great Artesian Basin. Many of these are yet to be developed but would involve significant groundwater extraction.

Great_Artesian_Basin2

Figure 2 – Map of the Great Artesian Basin showing active oil and gas leases. From: SoilFutures Consulting, (2015): Great Artesian Basin Recharge systems and extent of petroleum and gas leases (2nd ed)

Recently, a major international company has also proposed the largest coal mine in Australia’s history – the Carmichael Coal Mine & Rail Project. Within 10 kilometres of the proposed mine site is a group of Great Artesian Basin springs – the Doongmabulla Springs. These springs are an ecological refuge, providing an oasis of green in an otherwise dry landscape (as can be seen in drone footage here: https://www.youtube.com/watch?v=RglMko3GwQA). The springs are of high cultural and ecological significance to the local Indigenous Wangan and Jagalingou people, and for this reason (among others) these people are strongly opposed to the mine.

Colleagues of mine recently participated in a hotly contested court case, arguing over whether or not the Carmichael Mine poses a threat to the survival of the Doongmabulla Springs – recognised by the Land Court judge as having ‘exceptional ecological significance’. The argument centred on whether or not the springs are fed by water from the same group of aquifers that will be excavated and de-watered by mining, or shallower aquifers. Ultimately, the Court decided that the mine was unlikely to pose an imminent threat to the springs, and upheld the environmental authority that was earlier granted by the Australian Government. This was in spite of testimony of some expert hydrogeologists that the most likely explanation for the springs is a fault that brings deep groundwater to the surface (more about the case and the mine can be read here).

Protection of Great Artesian Basin Springs

In Australia, the native flora and fauna supported by Great Artesian Basin springs are protected under the country’s highest piece of environmental legislation – the Environment Protection and Biodiversity Conservation Act (1999). This recognises the extraordinary level of endemism in these spring systems – many support species that are found in a single spring pool or group of springs, and nowhere else on earth. If a mining project is located in an aquifer that supports ‘GAB Springs’, the Act specifies that the Environment Minister must impose conditions to protect the springs’ water source. The mining company must then develop a monitoring and management plan, and a set of contingency measures to ensure impacts can be minimised.

In order to protect the Doongmabulla Springs from potential impacts of the Carmichael mine, the Environment Minister chose to apply a drawdown limit or ‘trigger’ level of no more than 20cm, stating:

“I took a precautionary approach by imposing a drawdown limit of 20 cm at the Doongmabulla Springs Complex (condition 3d), to ensure that there are no unacceptable impacts to the springs”

Problems with a drawdown ‘trigger’ to protect springs

Limiting drawdown to 20cm at a spring may sound like a strict criterion to ensure minimal impact from groundwater extraction (as this is a relatively small change in the water level). However, the approach has a number of pitfalls, as I recently outlined in a technical commentary in an article for the journal Groundwater.

The drawdown ‘trigger’, applied at the springs themselves, ignores one of the fundamental principles of hydrogeology, which is that groundwater extraction affects aquifers in two major ways; firstly through depletion of water in storage, and secondly through capture of discharge. All groundwater and surface water systems are subject to a ‘water budget’, whereby an increase in extraction at one point leads to a corresponding decrease in water stored or water available somewhere else. It has long been recognised that when groundwater extraction begins, there is generally a period in which storage depletion – shown by declining groundwater levels in the aquifer near the extraction point – is the dominant effect. However, in the long-term, extraction is balanced mostly by a decrease in the discharge reaching the surface. It is the ‘capture of discharge’ which is the most important effect to consider when protecting springs from pumping – as spring water is entirely composed of groundwater discharge. Unfortunately, this ‘capture’ is not well predicted by monitoring the amount of drawdown, particularly at the point of discharge itself.

As Figure 3 below demonstrates, it is quite possible for a spring (or a gaining stream) to experience minimal drawdown, but for the flow of water from the aquifer to the surface to decrease or even cease entirely. For this reason, by the time 20cm of drawdown has been noticed at the Doongmabulla Springs – which are located about 8 kilometres from the mine site – it is likely that the flow directions and water budget will have been fundamentally changed, and possible that the springs may ultimately cease to flow, as has occurred in many other parts of the Great Artesian Basin.

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Figure 3 – Example of how groundwater levels change during groundwater extraction.  Drawdown may be small at a spring or stream until it is too late (fr: Currell, 2016).

Alternative approaches to management and protection of springs

It can be argued that the setting of a drawdown ‘trigger’ at a spring or stream is a classic case of ‘reactive’ environmental management, whereby management action is taken only in response to an impact when or after it takes place. Because of the relatively high level of uncertainty in most hydrogeological systems, the time-lags that occur between an activity such as pumping and the hydrological response, and the difficulty in directly observing groundwater behaviour, a pro-active approach to monitoring and managing impacts from mining and other activities is needed. As I argue in the technical commentary, a far more effective approach to springs protection would include a program to understand the source aquifer for the springs, an assessment of the water budget before and after the mining development (through modelling), and a monitoring program that maps out water level patterns and flow directions in the aquifer(s) regularly through time and also monitors flow rates at the springs. These activities should be undertaken up-front during the environmental impact assessment. If ‘trigger’ levels are to be used as an effective management tool,  these should be set as specified water levels at a series of points set back some distance from the springs, to identify negative effects before they reach the springs.

While this may sound onerous for the mining company, the importance of the springs to the indigenous people and ecological environment means that it is worth making the effort to use the best hydrogeological science possible to protect them.

Bonus Figures
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Artesian well in the Great Artesian Basin providing a constant flow of hot water. (Source: Wikipedia commons)

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Evidence of springs that have gone dry, from sites in Australia’s great Artesian Basin.  From: Fensham, R. et al., 2015 In search of lost springs: a protocol for locating active and inactive springs. Groundwater Volume 54, Issue 3, pagese 374-383, 5 October 2015 DOI: 10.1111/gwat12375 (link)

Human Drought?

Human Drought?

By Anne Van Loon – a water science lecturer at the University of Birmingham

Recently I published a commentary in Nature Geoscience with the title ‘Drought in the Anthropocene’. In that commentary, my co-authors and I argued that in the current human-dominated world, we cannot study and manage natural drought processes separately from human influences on the water system like water abstraction, dam building, land use change, water management, etc. To fully integrate human processes when studying drought we should change the definition of drought, test new methodologies and include social science. This sounds quite logical, but if you look at the history of drought science, it is not so obvious. In the natural sciences, drought research is a young field compared to research on floods. Floods are of course much more conspicuous, but drought causes more loss of life and economic damage worldwide. Because drought research is such a young field, the basic processes needed to be studied first before complex systems (including humans) could be understood. Additionally, much of the drought research in the last decades has focused on questions related to the effects of climate change, which needed natural case study regions, uninfluenced by people, for an undisturbed climate change signal.

So why do I think it is time for a change now? Well, partly because the drought research field is a more mature field now and because we realize that direct human influences on drought might be significantly bigger than the effects of climate change, but there is a personal story too. That story starts when I started my PhD on the processes underlying drought propagation at Wageningen University (the Netherlands) in 2007. I was going to focus on natural processes and five case study regions were selected in the EU-funded project I was working in. One of those ‘unfortunately’ was not a natural, undisturbed catchment. In the Upper-Guardiana catchment in Spain abstraction for irrigation in the 1980s and 1990s was so massive (see pictures below) that it decreased groundwater levels with 50 meters in some parts of the aquifer and groundwater-dependent rivers dried up (see pictures below).

A

Large-scale agriculture (mainly grapes) requiring large-scale irrigation in the Castilla-La Mancha region in Spain

 

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Dried-up rivers in the Guadiana catchment. The name of the river is even crossed out because there has not been any wate rflowing for 20 years. (Photos by Henny Van Lanen)

When the important Ramsar wetland Tablas de Daimiel dried up (see pictures below), this led to a debate between farmers and nature organisations. The nature organisations claimed this disaster to be caused by the agricultural abstractions, whereas the farmers defended themselves by arguing that the wetland dried up because of the severe multi-year drought that Spain was experiencing at the time and that their abstraction was only minimal. Since I was interested in the natural processes related to the development of that drought, I needed to exclude the effect of abstraction. I developed a methodology for that and discovered that the drying up of the wetland was caused by both a lack of precipitation and groundwater abstraction, but that the effect of groundwater abstraction on decreased water levels was, on average, four times as high as the effect of the lack of precipitation. This meant that both the farmers and the nature organisations were right, but the farmers had more influence than they claimed to have.

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Dried-up wetland Tablas de Dimiel. (Photos by Henny Van Lanen)

This approach of separating between the human and natural causes of a lack of water solved the problem for my PhD and I could comfortably go back to studying the natural processes of drought in all my case study regions. And I did so successfully, judged by the positive evaluation of my PhD thesis and defence in 2013 (see pictures below). However, something kept bothering me, because I realized that my results were not applicable to most of the world, since there are almost no places left without significant human influence on the water system.  Take the current multi-year drought in California. Politicians, farmers, water managers and the media keep asking the question: “how much rain is needed to end the drought?” This would already be quite a difficult question in a completely natural system, but it is un-answerable in a hugely complex system like California, dominated by human activities like agriculture, water abstraction, water storage in reservoirs, water transfer, and urbanization. How much rain is needed to end the drought is for example highly dependent on how much we abstract. With a simple water balance you can evaluate that the amount of water storage (in for example groundwater or reservoirs) is related to how much water comes in and how much water goes out. If we take out more, we also need more input to recover from a drought in storage. So, if the farmers in California keep on abstracting huge amounts of groundwater, the system will take much longer to recover. We as natural scientists cannot answer questions about the recovery of drought in these kind of human-dominated systems if we do not take into account human activities in our calculations. To be able to do that we need to adapt our methodologies. We could for example use the tools I used to get rid of human aspects of drought in my Guadiana case study, to instead focus on the effect of abstractions.

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PhD thesis and defense.

But it is not all bad. We can also have a positive influence on drought. Last year (already moved on to a Lecturer post at the University of Birmingham, UK), I visited Santiago de Chile for a project workshop. Santiago is a very big city (see pictures below). For its water supply the city is dependent on snow and reservoirs in the mountains. Decreasing snow accumulation related to climate change lead to worries about future water resources. One of the solutions the Chileans are investigating is artificial aquifer recharge projects, in which surface water during high-flow periods is led to infiltration ponds and allowed to recharge the underlying aquifer (see picture below). In times of low water availability in the mountains this groundwater can be used as alternative source of water.

E

The city of Santiage de Chile and their Artificial Aquifer Recharge project.

Also in Upper-Guadiana, people have found a solution to the problem. Measures are in place to reduce groundwater abstraction for irrigation. However, these take a long time to implement and to have an effect on groundwater levels and the wetland. Until that time, a temporary solution saves the important wetland from drying out completely. Groundwater is pumped up to keep the Tablas de Daimiel wetland wet (see pictures below). Hopefully this is a bridge to a more sustainable solution that results in a full recovery of the aquifer and the wetland.

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Re-wetted wetland Tablas de Daimiel.

These positive influences of humans, alleviating drought conditions, should also be included in our drought research, because then we can investigate the effectiveness of certain measures to reduce the impacts of drought. Responses to drought, such as water use restrictions, can lead to feedbacks between the natural and social systems that are very complex, but also very interesting and crucial to understand if we want to solve our drought problems. That is why I wrote the Nature Geoscience about such an obvious topic ‘Drought in the Anthropocene’. I am ready to work on more complex drought processes (see pictures below) and I encourage my colleagues to do the same so that our results are useful where they are most needed.

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Me looking towards a bright future … (Photos by Henny Van Lanen)

Read the paper ‘Drought in the Anthropocene’ here: http://www.nature.com/ngeo/journal/v9/n2/full/ngeo2646.html


Van Loon, A.F., Gleeson, T., Clark, J., Van Dijk, A., Stahl, K., Hannaford, J., Di Baldassarre, G., Teuling, A., Tallaksen, L.M., Uijlenhoet, R., Hannah, D.M., Sheffield, J., Svoboda, M., Verbeiren, B., Wagener, T., Rangecroft, S., Wanders, N. and Van Lanen, H.A.J. (2016). Drought in the Anthropocene. Nature Geoscience, 9(2), pp.89-91.


~ A repost from the TravellingGeologist blog ~

One hell of a great groundwater textbook now available free

One hell of a great groundwater textbook now available free

‘Groundwater’ the seminar text book from Freeze and Cheery (1979) is free in pdf now…just follow the links here. This text book is almost as old as I am and important parts of modern hydrogeology are rusty or non-existent (like hydroecology amongst other topics) but it is still lucidly written and useful.  I routinely send students to read chapters so I am happy that it is now available free.

Kudos to Pearson Publishing, Alan Freeze and John Cherry and Hydrogeologists without Borders! I look forward to Groundwater2.0 which is in the works!

 

 

The new and exciting face of waterunderground.org

The new and exciting face of waterunderground.org

by Tom Gleeson

I started waterunderground.org a few years ago as my personal groundwater nerd blog with the odd guest post written by others. Since I love working with others, I thought it would be more fun, and more interesting for readers, to expand the number of voices regularly posting. So here is the new face of the blog…

http://www.fragilestates.org/wp-content/uploads/2012/10/collective-action.jpg

a kind of weird image of collective action

What is the new blog all about?

Written by a global collective of hydrogeologic researchers for water resource professionals, academics and anyone interested in groundwater, research, teaching and supervision. We share the following aspirations:

  • approachable groundwater science at the interface of other earth and human systems
  • encourage sustainable use of groundwater that reduces poverty, social injustice and food security while maintaining the highest environmental standards
  • compassionate, effective supervision
  • innovative, effective teaching
  • transparency of scientific methods, assumptions and data

Check out more details and how to be part of the blog on about.

Frequent contributors include:

  • Andy Baker (University of New South Wales, Australia) – caves and karst (I actually visit the water underground!), climate and past climate
  • Kevin Befus (University of Wyoming, United States) – groundwater-surface interactions, coastal groundwater, groundwater age
  • Mark Cuthbert (University of Birmingham, United Kingdom) – groundwater recharge & discharge processes, paleo-hydrogeology, dryland hydro(geo)logy, climate-groundwater interactions
  • Matt Currell (RMIT University, Australia) – isotope hydrology; groundwater quality; transient responses in aquifer systems
  • Inge de Graaf (Colorado School of Mines, United States) – global groundwater withdrawal, flow and sustainability
  • Grant Ferguson (University of Saskatchewan, Canada) – groundwater & energy, regional groundwater flow, sustainability
  • Tom Gleeson (University of Victoria, Canada) – mega-scale groundwater systems and sustainability
  • Scott Jasechko (University of Calgary, Canada) – global isotope hydrology; groundwater, precipitation, evapotranspiration
  • Elco Luijendijk (University of Gottingen, Germany) – paleo-hydrogeology,deep groundwater flow,large scale groundwater systems
  • Sam Zipper (University of Wisconsin – Madison, United States) – ecohydrology, agriculture, urbanization, land use change

Just in case you weren’t sure…groundwater flow around a fault zone is complex!

Just in case you weren’t sure…groundwater flow around a fault zone is complex!

By Erin Mundy – a plain language summary of part of her Masters thesis

Groundwater is the water that collects underground in pores and cracks in the rock. Understanding, protecting and sustaining groundwater flow is critical because over two billion people drink groundwater every day. The flow of groundwater can be impacted by geologic structures, such as fractures and faults. A fracture is a break in the rock; a fault is a break in the rock where the rocks move relative to each other (ie. one rock will move up, one rock will move down, as seen in Figure 1).

CTF1

Figure 1. Diagram of a thrust fault

Faults can act as barriers slowing down groundwater flow, they can be a conduit speeding up groundwater flow, or amazingly they can act both slow it down and speed it up!

How groundwater moves through these rock structures is difficult to directly observe because it all happens underground and rarely exposed on the surface. The Champlain thrust fault at Lone Rock Point in Burlington, Vermont, provides a unique opportunity to study groundwater flow around a fault because approximately 1 km of the fault is exposed along the edge of Lake Champlain (Figure 2). Here, an older rock

CTF2

Figure 2: Photograph of the Champlain Thrust fault at Lone Rock Point, Burlington, Vermont. Note the person at the bottom right for scale

(yellow) is thrust over a younger rock (black). No one has studied groundwater flow around this fault in detail, so we hoped to find out a basic understanding of the relationship between the fault and groundwater flow at this location.

To understand groundwater flow around this fault, we did three things: 1) we walked along the fault and made note of changes in the fault (ie. the width of the fault, the angle of the fault, the shape of the fault, etc.); (2) we looked for areas where groundwater was leaking from the rock surface (this is known as groundwater seepage – we wanted to see if there was a relationship between where groundwater was leaking out and the changes in the angle/width of the fault); and (3) we drilled three wells and then pumped water out of these wells. We pumped water out of one well and measured the water level in the other wells – this gives you an idea of how the groundwater moves. For example, if you pump water out of one well and the water level in a nearby well declines drastically, this suggests that the water is easily moving through the rock. So if you’re pumping water from the fault and that happens, then the fault is most likely channeling water along the fault. If the opposite happens, then the fault may be acting as a barrier to groundwater flow.

We found four main geologic structures at the Champlain thrust fault: (1) the main fault, (2) an area where the fault splayed into many smaller faults, (3) areas where the fault thickness increased to 3 m, and (4) areas where there are traces of older, cemented fault rock (Fig. 3).

CTF3

Figure 3. Most important structures we observed at the Champlain thrust fault. the thin dashed white line follows the main fault, thicker black dashed line follows the main structural features. Hanging wall is the older rock; footwall is the younger rock. a) main fault; b) fault splay; c) increased fault thickness; and d) older abandoned fault rock

We found 19 areas along the rock where groundwater was leaking out of the cliff (Note: This was done in the winter so the groundwater was frozen into ice). We found that most of the groundwater seepage occurred in the younger (black) rock, with a few at the fault and where the fault splays out into smaller faults (Figure 4).

CTF4

Figure 4. Seeps located a) at the intersection of a multi-stranded fault structure and b) at the fault core. Note measuring tape for scale (1 foot)

While drilling the two wells at the site, we had two unexpected problems. One, there was a large difference between the depth of the fault in the two wells. The fault depth in one well was 27.4m, while in the other well (which was 10 m away), the fault depth was 70 m. This suggests that there must be another fault in between these two wells that offsets the fault depth. The other unexpected complication was that we drilled into 1.8 m and 2.1 m caves beneath the ground. Caves are common features in limestone, but the rock at our site is a dolostone, which is usually more resistant, so caves are an interesting find! The pumping test revealed a complex system. Further testing is needed to better refine these results.

Combining the data from the surface and subsurface observations, we created a preliminary three-dimensional model of the Champlain thrust fault (Figure 5). Where the rock is exposed at the edge of Lake Champlain, the fault thickness varies, splaying out into smaller faults and showing traces of older fault rock. Groundwater is leaking out of the younger rock (footwall) and along the fault. At the well-site, the fault is offset by another fault and caves are present. The three approaches we used (geology, seepage, pumping tests) all revealed different aspects of the Champlain Thrust fault, and exposed the complexity of groundwater flow around faults.

 

CTF5

Figure 5. Three-dimensional conceptual model of the Champlain thrust fault.

 

Can we use an infrared camera to tell us how much groundwater is coming out of the side of a cliff?

Can we use an infrared camera to tell us how much groundwater is coming out of the side of a cliff?

By Erin Mundy – a plain language summary of part of her Masters thesis

Groundwater is an important resource, with approximately 2 billion people around the world using groundwater everyday. Although most groundwater is beneath our feet, sometimes groundwater leaks out of stream-banks, hill sides and cliff faces – this is called groundwater seepage. Current scientific methods are not able to measure the amount of groundwater that leaks out of these landscapes. Scientists have used infrared cameras (cameras that show the heat of an objects) to identify groundwater seepage on hill-slopes and stream banks (Figure 1).

seep1

Figure 1. Digital image (a) and temperature image (b) of a seep in the summer and a digital image (c) and temperature image (d) of the same seep in the winter

This is because groundwater has an distinct heat signal, having a relatively constant temperature throughout the year (~10 degrees Celsius). Building on these studies, we hoped to find out the possibilities and limitations of using infrared cameras to measure the amount of groundwater that leaks out of the side of a cliff. We wanted to test if groundwater was flowing out of a cliff face slowly in the summer would warm up as it traveled down the rock, so the heat signature of the groundwater would go from cool water (that comes out of the rock, ~10 °C) to warmer water (warmed due to the sun and air temperature). On the other hand, we wondered if groundwater was flowing fast out of the cliff-face, it would not have time to warm, because the cool groundwater would be consistently running over it. In the winter, we believed the opposite would happen, that the groundwater would be warmer, relative to the surroundings, and show a cooling trend as the water traveled down the rock.

 

We found an unused mining pit in Saint Dominique, Quebec, that had lots of groundwater seeps coming out of the exposed rock, and used this as our test location. The mining pit had 3 different levels, as shown in Figure 2.

seep2a

Figure 2: an aerial shot of the quarry with the seeps labeled.

We took infrared and optical photographs of the seeps during seven visits that spanned from January 2013 – October 2014. Three visits took place during the winter (January – February 2013), coinciding with periods of below freezing so that the effect of extreme cold on seeps could be analyzed. Four visits took place during the summer/fall (June – October 2014), coinciding with sunny and hot conditions, and cloudy and warm conditions in order to determine the effect warmer temperatures have on seepage. In addition to these visits, we also completed a 24-hour experiment, where we took infrared pictures of two seeps every half hour for 24-hours, to determine the effect of sunlight and changing air temperature on the seep temperature signature. We also created an “artificial seep” experiment, where we released water from two large tubs over the cliff at the pit for 8 hours; one tub had water released at a slow rate, while the other at a faster rate, to see if we could replicate the heat signals from the real seeps. We took pictures with the infrared camera every half hour for eight hours for that experiment. We analyzed the infrared photos from each visit using a computer software that allowed us to determine the temperature along the seep.

In the winter, groundwater flows out the rock at warmer temperatures than it’s surroundings, making it easily distinguishable. We found that there was a clear relationship between seeps with active groundwater flow and areas of ice growth on the following visit. So, in the winter, if you use an infrared camera to locate where groundwater is flowing on the side of a cliff, you can assume there is a good chance that ice will eventually form at these spots. However, the groundwater did not cool along the rock face, as we had expected it would. This suggests frozen seeps are complex and it is unlikely that temperature pictures can determine the rate of flow of groundwater seeps in the winter.

In the summer, we found that lower flowing seeps did warm up as the water traveled down the rock face, as compared to faster flowing seeps, which did not show as much warming. However, in the 24-hour experiment (where we took infrared pictures every half hour for 24 hours of two seeps), we found that the temperature signature of the seeps changed throughout the day. During the day, there was much more warming of the groundwater as it traveled down the cliff, whereas at night it did not warm as much. This is most likely due to the presence of sunlight and warmer air temperature during the day, which warms the water more as it is traveling down the rock.

In the “artificial seep” experiment, we found that the “seeps” showed more warming than the real seeps. This is probably because we only ran the experiment for 8 hours, so it did not have time to mimic the conditions of real seeps. Also, we noticed that instead of flowing down the rock face, some of the water was actually seeping into the rock, along the breaks in the rock. This may be another reason why the seeps showed more warming, as not enough water was flowing down the rock (instead it was flowing into it).

After completing these experiments, we have concluded several possibilities and limitations for infrared pictures of groundwater seeps.

Possibilities:

  • Locate groundwater seeps in all seasons
  • Locate groundwater seeps in winter and from this, areas of ice growth can be predicted
  • Distinguish between lower flowing seeps and higher flowing seeps in summer (lower flowing seeps have more warming as the water travels down the rock face, higher flowing seeps do not have as much warming)

 Limitations:

  • Need to have a large difference in temperature between the air and groundwater to notice seeps. During the third winter visit, only one seep was identified to be flowing by the infrared camera. However, visual observations showed that eight seeps had groundwater flowing. This is because the temperature of the groundwater was too similar to the temperature of the air, making it not possible to detect the groundwater flow.
  • Groundwater seeps in the winter are complex and do not show a cooling trend, therefore it is unlikely that temperature pictures can determine the rate of flow of groundwater seeps in the winter
  • Breaks in the rock affect the flow of seeps, redirecting the flow, making it hard for temperature pictures to accurately determine flow
  • Sunlight and air temperature affect the “warming” and “cooling” of the groundwater flow, with more warming present during the day and less at night. Focus needs to be on determining the optimal time to use infrared pictures to show the “warming” (or “cooling”) trend.
  • The infrared camera itself has limitations. To use some functions of the camera, you have to correct your data for certain factors (like angle of the camera, humidity, etc.). If you don’t, you won’t be showing accurate data. This limits the amount of things you can do with the infrared camera and must be taken into account in order to ensure the pictures you captured are correct.

 

Despite the large number of limitations, infrared pictures is effective at locating groundwater seeps in all seasons, and able to distinguish between lower flowing seeps and higher flowing seeps (in the summer), which makes this technique a valuable, non-invasive way to study groundwater seepage. Future work should look at determining the optimal time to capture infrared pictures of seeps to determine a relationship between groundwater flow and temperature signatures.

 


 

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