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Good groundwater management makes for good neighbors

Good groundwater management makes for good neighbors

Post by Samuel Zipper, postdoctoral fellow at both McGill University and the University of Victoria, in Canada. You can follow Sam on Twitter at @ZipperSam.

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Dedicated Water Underground readers know that this blog is not just about water science, but also some of the more cultural impacts of groundwater. Keeping in that tradition, today’s post begins with a joke*:

Knock, knock!

Who’s there?

Your neighbor

Your neighbor who?

Your neighbor’s groundwater, here to provide water for your plants!

Figure 1. Typical reaction to joke written by the author.

Ahem.

Perhaps this joke needs a little explanation. As we’ve covered before, groundwater is important not just as a supply of water for humans, rivers, and lakes, but also because it can increase the water available to plants, making ecosystems more drought resistant and productive. However, we also know that groundwater moves from place to place beneath the surface. This means that human actions which affect groundwater in one location, like increasing the amount of paved surface, might have an unexpected impact on ecosystems in nearby areas which depend on that groundwater.

Imagine, for example, two neighboring farmers. Farmer A decides retire and sells his land to a developer to put in a new, concrete-rich shopping center. Farmer B continues farming her land next door. How will the changes next door affect the groundwater beneath Farmer B’s land, and will this help or hurt crop production on her farm?

In a new study, my colleagues and I explored these questions using a series of computer simulations. We converted different percentages of a watershed from corn to concrete to see what would happen. Our results showed that the response of crops to urbanization depended on where the land use change occurred.

Figure 2. Conceptual diagram showing how urbanization might impact crop yield elsewhere in a watershed. From Zipper et al. (2017).

In upland areas where the water table was deep, replacing crops with concrete caused a reduction in groundwater recharge, lowering the water table everywhere in the watershed – not just beneath the places where urbanization occurred. This meant that places where the ecosystems used to be reliant on groundwater could no longer tap into this resources, making them more vulnerable to drought. However, places where the water table used to be too shallow saw boosts in productivity, as the lower water table was closer to the optimum water table depth.

In contrast, urbanization happening in lowland areas had a much more localized effect, with changes to the water table and yield occurring primarily only in the location where land use changed, because the changes in groundwater recharge were accounted for by increased inflows from the stream into the groundwater system.

So, what does this mean for the neighboring farmers we met earlier?

For Farmer A, it means the neighborly thing to do is work with the developers to minimize the effects of the land use change on groundwater recharge. This can include green infrastructure practices such as rain gardens or permeable pavement to try and mimic predevelopment groundwater recharge.

For Farmer B, the impacts depend on the groundwater depth beneath her farm. If the groundwater beneath her farm is shallow enough that her crops tap into that water supply, she should expect changes in the productivity of her crops, especially during dry periods, and plan accordingly.

*Joke written by scientist, rather than actual comedian.

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For More Information:

Zipper SC, ME Soylu, CJ Kucharik, SP Loheide II. Indirect groundwater-mediated effects of urbanization on agroecosystem productivity: Introducing MODFLOW-AgroIBIS (MAGI), a complete critical zone model. Ecological Modelling, 359: 201-219. DOI: 10.1016/j.ecolmodel.2017.06.002

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Sam Zipper is an ecohydrologist. His main research focuses broadly on interactions between vegetation and the water cycle, with a particular interest in unintended or indirect impacts of land use change on ecosystems resulting from altered surface and subsurface hydrological flowpaths. You can find out more about Sam by going to his webpage at: samzipper.weebly.com.

Of Karst! – short episodes about karst

Of Karst! – short episodes about karst

Episode 2: Dissolving rock? (or, how karst evolves).

Post by Andreas Hartmann, Lecturer in Hydrology at the University of Freiburg (Universität Freiburg), in Germany. You can follow Andreas on twitter at @sub_heterogenty.

Didn’t get to read Episode 1? Click this link here to do so!

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In the previous episode, I introduced karst by showing how it looks in different regions in the world. This episode will now deal with the processes that create such amazing surface and subsurface landforms. The widely used term “karstification” refers to the chemical weathering of easily soluble rock composed of carbonate rock or gypsum. Most typical is karstification of limestone (consisting of the mineral calcite, CaCO3) or dolostone (consisting of the mineral dolomite, CaMg(CO3)2). If exposed to CO2 rich water these rocks are dissolved to form aqueous calcium (Ca2+) or magnesium (Mg2+) and bicarbonate (HCO3 ) ions. For calcite, karstification is described by the following chemical equilibrium:

The dissolution of carbonate rock depends on various factors. Imagine a solid block of salt, which you pour water on. If completely solid, the water will flow down the salt surface slowly dissolving the block. If fractured, water will eventually enlarge the fractures in the salt block and dissolution will occur much faster. Now imagine smashing the salt block before pouring water on it. In such circumstances the salt will dissolve even faster as the surface area exposed to the water is much larger.

Karst and its evolution (educational video provided by Jennifer Calva on Youtube).

The same is true for karstification. If the carbonate rock is heavily fractured, it will dissolve faster than unfractured carbonate rock. Another factor is the availability of CO2, that depends on the relative amount of CO2 in the air, air temperature and soil microbiotic processes. Other factors are the purity of the carbonate rock, the availability of water, and the supply of CO2 from the surface. As soon as karstification takes place, more water will be able to pass the dissolution enlarged fractures providing more and more CO2, and creating a positive feedback between rock dissolution and water flow:

Positive feedback between carbonate rock dissolution and water flow (Hartmann et al., 2014, modified).

The hydrochemical processes described in this episode of the Of Karst! Series not only create beautiful karst landscapes but they also have a strong and particular impact on water flow paths in the subsurface, which will the topic of episode 4 that can be expected in early 2018. Before, I will present a special feature about karst in the movies as topic of episode 3 in autumn 2017.

Further reading

Hartmann, A., Goldscheider, N., Wagener, T., Lange, J. & Weiler, M. 2014. Karst water resources in a changing world: Review of hydrological modeling approaches. Reviews of Geophysics, 52, 218–242, doi: 10.1002/2013rg000443.

Ford, D.C. & Williams, P.W. 2013. Karst Hydrogeology and Geomorphology. John Wiley & Sons, 576 pages.

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Andreas Hartmann is a lecturer in Hydrology at the University of Freiburg. His primary field of interest is karst hydrology and hydrological modelling. Find out more at his personal webpage www.subsurface-heterogeneity.com.

 

Groundwater & Education – Part One

Groundwater & Education – Part One

Post by Viviana Re, postdoctoral researcher at the University of  Pavia (Università di Pavia), in Italy. You can follow Viviana on Twitter at @biralnas.

Part one of a two part series on groundwater and education by Viviana.

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Education /ɛdjʊˈkeɪʃ(ə)n
The process of receiving or giving systematic instruction, especially at a school or university.

  • from Latin educatio(n-), from the verb educare
  • Educare is a combination of the words e (out) and ducare (lead, drawing), or drawing out.

Based on this definition, I should change the title of this post to: Drawing out groundwater (from the well). This is actually the main occupation of groundwater scientists, isn’t it? Not only are we always withdrawing groundwater from a well or a borehole while sampling, but we also often have to “draw it out” when dealing with managers and policy makers, as sometimes they seem to forget about this hidden (but very important) component of the water cycle. Therefore, we are quite used to these forms of “drawing out” – but what about education? Are we really that effective in “drawing out” groundwater in explaining its peculiarities, issues, and connections within the whole water cycle and, more generally, with the environment?

Indeed, the effort of shedding light on something that is not so visible nor easily studied has the side effect of forcing us to focus solely on it, with a resulting tendency of developing sectorial approaches to water management.

In the preface of a UNESCO Technical paper, I found the following excerpt: “Water resources schemes are now increasingly considered as integrated systems and consequently, civil engineers, geologists, agricultural engineers and hydraulic engineers engaged in planning and design no longer work in isolation”. The document is dated 1974 but, still in 2017, we are somehow struggling to fitting groundwater into Integrated Water Resources Management (IWRM) and to connecting mental and structural “silos”. Quoting Daly (2017), the latter is particularly relevant (especially when education is at stake): if on the one hand, specialization can be the driver for a sound knowledge; on the other hand, this can encourage people to get stuck in their own individual disciplines (or said in other words, their “silos”). Indeed, “silos” exist in their structures, but can also exist as a state of mind that can go hand in hand with tunnel vision (Tett, 2015).

Therefore, in my opinion, the new generation of groundwater scientists (and teachers) should have a new mission: to work (and therefore, to teach) coherently with the integrated and complex nature of the water cycle. In fact, the role of hydrogeologists and groundwater scientists in times of increasing freshwater demand, exacerbated by population growth and climate change effects, requires a serious shift towards a more holistic approach targeting sound groundwater assessment and long-term management.

Arguably, if we are still discussing possible ways of practically implementing this integration, we should definitely start asking ourselves if the the “business as usual” way of working and teaching is effective.  If it is not, we must begin investigating how we can go beyond classical approaches to draw groundwater out of the well.

Playing with kids while sampling … can we call it capacity building?!

 

To be continued …

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Is highway de-icing ‘a-salting’ our aquifers?

Is highway de-icing ‘a-salting’ our aquifers?

Post by Mark Cuthbert, Cardiff University, and Michael Rivett, GroundH20 plus Ltd; University of Strathclyde.

If you live in a cold climate, have you ever wondered where all the de-icing salt (or ‘grit’ as we call it in the UK) that gets spread on the roads in winter time ends up, aside from that accumulating salty grime that coats your car? As you might expect, most of the salt gets washed off the highways as the salt has the desired effect of melting the ice, or carried away by rain. This salty ‘runoff’ ends up in streams nearby via pipes which drain the highway. However, that is not the end of the story…

We studied a major highway intersection on the edge of UK’s second largest city, Birmingham (more than a million people), to see how much of the salt spread on the highway ends up in groundwater. Our interest stems from concerns of the national regulator to understand not only how much salt ends up in streams, but also the potential long-term build-up of salt in underlying groundwater resources that are pumped for public and private water supply. Although the origin of salt in streams and lakes is relatively well studied, the pathways by which salt moves from highways to groundwater are poorly understood and quantified.

The various ways salt could be getting in to the groundwater are shown in Figure 1 and a bit of detective work was required to find out what was going on.

Figure 1*

This involved dressing in silly (and warm) clothes, and pulling our equipment around on a sledge, which was a lot of fun (see photos below).

The authors, Mark (left) and Mike (right), enjoying some urban winter fieldwork.

Our main field activities were fortuitously timed to include the severe winters of 2009-10 and 2012-13. We collected information about the amount of salt spread on the roads and measured the salt concentrations in the local streams, as well as in the shallow and deep groundwater wells in the area around the highway network.

7 km of motorway drained to the studied stream. Over the winter of 2012-13 we estimated that around 510 tonnes of de-icing salt was applied to the highway and major road network across the catchment. Most of that washed off the road via drains when it next rained or as the snow and ice melted, and ended up in the stream which flows under the highways. Some of it ended up on the roadside verges – this was not quantified, but would likewise eventually leach into the underlying groundwater over time.

We estimated about 12% of the de-icing salt, that’s around 63 tonnes over the 2012-13 winter, leaked through the bottom of the stream channel into the groundwater in the sandstone aquifer beneath, and may pose a risk to groundwater supplies in the area (see “9” in Figure 1, and results in Figure 2). While increases in groundwater chloride concentrations observed to date have been modest, and fortunately remain far below the drinking water standards, the steady year-upon-year build-up of salt in groundwater remains a concern. This is especially the case as the UK’s de-icing salt applications reached record levels in the recent severe winters and add to a potential de-icing salt legacy in our aquifers that has accumulated now over some 50 plus years.

Figure 2*

So how concerned should we be that so much salt is flowing down these streams and into the groundwater around our highways? There isn’t yet a simple answer to that but, with a global trend towards increasing urbanisation, this is an important area of ongoing and future research.

 

Further details of our published research to date on the Birmingham case study may be found at:

Rivett, M.O.,  Cuthbert, M.O., Gamble R., Connon, L.E., Pearson, A., Shepley, M.G., Davis, J., 2016. Highway deicing salt dynamic runoff to surface water and subsequent infiltration to groundwater during severe UK winters.  Science of the Total Environment 565, 324-338. http://dx.doi.org/10.1016/j.scitotenv.2016.04.095 (*figures reproduced with permission) [Read More]

How did our planet get its water?

How did our planet get its water?

Post by WaterUnderground contributors Elco Luijendijk and Stefan Peters from  the University of Göttingen, in Germany.

After my first ever scientific presentation, someone in the audience asked a question that caught me off guard: “Where does the groundwater come from?”.  “Ehm, from rainfall”, I answered. The answer seemed obvious at the time. However, we did not realize at the time that this is actually a profound question in hydrogeology, and one that is rarely addressed in hydrology textbooks and courses: “How did our planet get its water?”. To find out how far science has come to answering this question I (EL) joined up with a geochemist and meteorite expert (SP) to write this blog post.

We are lucky to live on a planet of which ~71% of the surface is covered with water, located mostly in rivers, lakes, glaciers and oceans at the surface and as groundwater in the shallow subsurface. Liquid water sustains life on our planet and seems to play a critical role in plate tectonics. And incidentally, it also to gives hydrogeologists something to study. Liquid water is so important in sustaining life, that the search for life on other planets in our solar system or beyond always focuses first on finding planets with liquid water.

Not only do we have abundant liquid water, we seem to have just the right amount. Compared to our direct planetary neighbors, Mars and Venus, we are extremely lucky. On the surface of Mars, at present, water mainly occurs as ice, whereas tiny amounts of water vapor are present in the Martian atmosphere. Venus also has minute amounts of water vapor in the atmosphere, but its blazingly hot surface is entirely devoid of water. In contrast to Mars and Venus, some objects in the solar system that are further away actually have too much water. Take for instance Enceladus, a moon of the planet Saturn, at which an icy crust overlies a 10 km deep water ocean. The amount of water on Enceladus is so large that it causes a wobble in the rotation of this moon, which is one of the reasons why this large volume of water was discovered in the first place. Clearly Enceladus is great for ice-skating, but probably not for sustaining land-based life similar to humans.

Figure 1: From left to right, Venus, Earth and Mars. Which one would you like to live on? Source: ESA (link) .

So how did we on Earth get so lucky?

It turns out that this depends on which scientist you ask. There are two theories:
Theory 1: The major building blocks of the Earth contained water from the start. This water then accumulated at the surface of our planet (by “degassing” from the mantle) and formed the oceans and the hydrosphere.
Theory 2: The major building blocks of the Earth were bone dry, and most of the water was delivered by comets and water-rich asteroids some time after most of our planet’s mass had formed by accretion.
So far, scientists do not have reasons to discard either of these theories, but there are two important arguments in favor of water being delivered after most of the planet had already formed:

Earth formed in a hot region of the solar system from which molecules with “low” condensation temperatures such as water had largely been removed before planetary accretion started (Albarède, 2009). Secondly, the ratio of heavy to light water in Earth’s oceans is similar to that of water in some comets and asteroids (Hartogh et al., 2011). Although you may not have noticed this when you last opened your water tap, a very small fraction (0.016 %) of the water on our planet is heavy, because it contains an extra neutron. The similarity in heavy water composition between asteroids and comets and Earth’s oceans does not prove that water on Earth was delivered by comets, but it certainly is consistent with this scenario. To make matters more complicated, however, the recent European space agency mission Rosetta to the water-rich comet 67P/Churyumov–Gerasimenko found that it has a very different ratio of heavy to light water than our oceans, which certainly complicates the debate.

Figure 2 Comet 67P/Churyumov-Gerasimenko losing water (and dust) as it gets closer to the sun. Source: ESA

Interestingly, neither theory can directly explain why our direct planetary neighbors, Mars and Venus, are so dry compared to Earth. So is it possible that these planets once were similar to Earth, and contained more water in their early days than that they do now?

Due to the high surface temperatures at Venus, any liquid water near the surface would immediately evaporate and diffuse into the atmosphere of the planet as a gas. We know that due to the lack of a protective magnetic field on Venus, solar winds continuously erode the atmosphere of the planet. If Venus had abundant water in the past, such erosion by solar winds would therefore have effectively stripped water from the planet’s atmosphere. Similar to Venus, Mars also does not have a protective magnetic field, but the temperatures and pressures at the Martian surface are significantly lower than at Venus’ surface, allowing water to be present at the surface as ice. In fact, Mars may have had a denser atmosphere in the past that allowed liquid water to be present at the surface. Nowadays, erosional features such as channels are the dry witnesses that water indeed once occurred as a liquid on the surface of the planet.

Figure 3. Dry channels (in inverted relief) in the Eberswalde delta on Mars as seen by NASA’s Mars Global Surveyor (link)

As a summary, we have an idea on why our planet was lucky enough to keep large amounts of water compared to Venus and Mars. However, do we know how our planet got its water in the first place? Unfortunately we are still not sure. There is hope though: we keep getting closer to the answer thanks to recent research on the composition of water on our planet and comets and asteroids in the solar system. So stay tuned, there’s a good chance that science will be able to answer this question in the coming years…

References
Hartogh, P. et al. (2011), Ocean-like water in the Jupiter-family comet 103P/Hartley 2, Nature, 478(7368), 218–220.
Albarède, F. (2009). Volatile accretion history of the terrestrial planets and dynamic implications. Nature, 461(7268), 1227-1233.

Limits to global groundwater use

Limits to global groundwater use

Post by WaterUnderground contributor Inge de Graaf. Inge is a postdoc fellow at Colorado School of Mines, in the USA.

Groundwater is the world’s most important source of freshwater. It supplies 2 billion people with drinking water and is used for irrigation of the largest share of the world’s food supply.

However, in many regions around the world, groundwater reserves are depleting as the resource is being pumped faster than it is being renewed by rain infiltrating through the soil. Additionally, in many cases, we are still clueless about how long we can keep drawing down these water reserves before groundwater depletion will have devastating impacts on environmental and socio-economic systems. Indeed, these devastating effects are already being observed.

The most direct effect of groundwater depletion is the decline in groundwater levels. As a direct impact, groundwater-pumping cost will increase, so too will the cost of well replacement and the cost of deepening wells. One of the indirect consequences of declining water levels is land subsidence, which is the gradual sinking of the surface. In many coastal and delta cities, increased flooding results in damages totaling billions of dollars per year. Next to this, declining groundwater levels lead to a decrease in groundwater discharge to rivers, wetlands, and lakes, resulting in rivers running dry, wetlands that are no longer sustained, and groundwater-dependent ecosystems that are harmed.

Over the past decades, global groundwater demands have more than doubled. These demands will continue to increase due to population growth and climate change.

The increase in demands and the aforementioned negative effects of groundwater depletion raise the urgent question: at what time in future are the limits to global groundwater use reached? This is when and where groundwater levels drop to a level where groundwater becomes unattainable for abstraction, or that groundwater baseflows no longer sustain river discharges.

In my PhD research, I predicted where and when we will reach these limits of groundwater consumption worldwide. I defended my dissertation last year April at Utrecht University, in the Netherlands.

Where and when are the limits reached?

Results show that many large aquifer systems are already highly depleted, especially for intensively irrigated areas in dryer regions of the world, like India, Pakistan, Mid West USA, and Mexico (see Figure 1). New areas experiencing groundwater depletion will develop in the near future, such as Eastern Europe and Africa. Future predictions show that some areas, like the Central Valley, and the High Plains Aquifer, partly recover when more recharge will becomes available. Notwithstanding, environmental groundwater demands will increase as to buffer more irregular streamflow occurrences due to climate change.

Figure 1: Estimated groundwater depletion (1960-2010) in [m], masked for aquifer areas, and zooms for hotspot regions, which are the intensively irrigated regions of the world.

In 2010, about 20% if the world population lived in groundwater depleted regions, where groundwater dropped below the economical exploitable limit. As a rule of thumb: the economic limit is reached when groundwater becomes unattainable for a local farmer, which is approximately when the water level drops to 100 m below the surface. In 2050, 26% to 36% of the world’s population will live in areas where the economic exploitable limit is reached (see Figure 2). Evidently, this persistence and increasing level of groundwater stress will impair local development and generate tension within the global socio-economic system.

Figure 2: First time that groundwater falls below the 100m limit.

 

Global-scale simulations

To answer my main question, I studied the effects of groundwater abstractions on river low flows and groundwater levels worldwide, as well as which trends in river low flow frequency and groundwater level change can be attributed to groundwater abstractions.

I used a newly developed physically based surface water-groundwater model to simulate i.a. river flows, lateral groundwater flow, and groundwater-surface water interactions at a high resolution (approx. 10×10 km) at the global scale. Total water demands were estimated and account for agricultural, industrial, and domestic demands. I simulated groundwater and surface water abstractions based on the availability of the resource, making the estimate reliable for future projections under climate change and for data-poor regions where we do not know how much groundwater or surface water is abstracted. Next, I developed a global-scale groundwater model. I estimated alluvial aquifer thickness worldwide, as no data at the global scale is available (see Figure 3). Aquifer thickness is one of the parameters you need to estimate groundwater flow and storage.

Figure 3: Estimated alluvial aquifer thickness. White areas are mountain regions, where no aquifers are simulated.

Simulations were done for the recent past and near future (1960-2050) and the results include maps and trends of groundwater heads, groundwater fluctuations, and river discharges.

In conclusion, most of our water reserves are hidden underground and most of our groundwater abstractions rates exceed groundwater renewing rates, leading to depletion. The growing demand and the expected climate change bring our groundwater reserves under mounting pressure. More than two-thirds of all abstracted groundwater is used for food production. Every year the world’s population is growing by 83 million people.

Improving our knowledge about how much water we can use in the near future while avoiding negative environmental and socio-economic impacts is therefore extremely important. A study like this contributes to the knowledge gap and can help guide towards sustainable water use worldwide to overcome potential political water conflicts and reduce potential socio-economic friction, as well as to secure future food production.

Want to read more? Check out the recent AGU press release or if you have more time… read my papers on dynamic water allocation (click here), development of a global groundwater model (click here, or here), or read my PhD thesis (here).

 

Author Inge de Graaf receiving her PhD degree from her advisor, professor Marc Bierkens (at Utrecht University, Netherlands). Note Tom Gleeson’s bald head in the lower left…

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.

Ogallala_WithMap.png

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

irrigation-sprinkler-large

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

PlatteRiver

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

Ogallala.jpg

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.

KB1

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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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).

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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

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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).

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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).

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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.

 

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

 

Nature Geoscience digging into water underground this month!

Nature Geoscience digging into water underground this month!

Nature Geoscience is digging hard into water underground – the February issue is part of a special focus on groundwater. The cover this month is a gorgeous (groundwater-filled?) waterfall by Glen Jasechko, Scott’s brother.  The groundwater focus includes:

As part of the focus the journal made our paper on modern groundwater free to registered users for a month – so go download it an check out this and the other papers too!

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