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Crop kites

Crop kites

Post by WaterUnderground contributor Mikhail Smilovic. Mikhail is a PhD  candidate in the Department of Civil Engineering at McGill University, in Quebec.

Crops use water for photosynthesis, absorbing nutrients, and transpiration, or the plant-equivalent of sweating. A crop may experience water-stress if the soil surrounding the roots is not adequately wet, and this stress will affect the crop differently depending on the crop’s stage of growth. Irrigation is the watering of plants to ultimately avoid such water-stress.

Non-irrigated crops are more vulnerable to intervals of dry and hot weather, and the increasing unpredictability of a changing climate will further complicate other crop management tools, such as choosing different cultivars (the particular variety of crop, some which may deal with certain stresses in an improved way) or changing planting dates.

Irrigated crops do not experience water stress (they may in fact experience water stress under a non-perfect irrigation system, but forgive this for now), but the water is necessarily derived from somewhere else. This somewhere else may also experience water withdrawals from municipalities, industry, and other agriculture. The source of water may be underground, or water from a river, lake, or spring, but a connection between both underground and surface waters shares with us that water removed from a system somewhere will have a response somewhere. This somewhere may very well be an ecosystem. Irrigation may also be costly related to the abstraction, transportation, and on-farm distribution.

Between non-irrigated and irrigated is a curious place where we can increase the resiliency of our agricultural systems to periods of drought and heat with limited irrigation, while allowing crops to experience well-timed water stress. Agricultural productivity or yield is determined as the amount of crop produced per area of land, say 3 tons/hectare for wheat. When water is a limiting factor, we would be sensible to also consider water productivity, that is the ratio of crop yield and water use, or, the amount of crop produced per drop of water. The practices of limited irrigation, also known as supplemental or deficit irrigation, makes an effort to increase this water productivity.

This space in-between non-irrigated and irrigated, however, has been often poorly explored or simplified. Crop kites is a novel tool to determine and quantify the potential agricultural and water productivity associated with different irrigation practices. This is important for regions interested in shifting investments into or away from irrigation, as well as for researchers interested in evaluating limited irrigation practices as initiatives to establish food and water security, both currently and with changing climates.

A first thought might be, if a crop uses three quarters of the water than it would under ideal conditions, does the crop produce three quarters as much as the crop under ideal conditions? In fact, the answer depends very much on when this water is used.

Let us take the example of winter wheat in northern Africa. Winter wheat can be broadly characterized into five different growth stages. We can illustrate water use throughout the season with the following figure:

Water use is represented by the bottom blue colour, and the associated deficit is represented with the upper orange colour – the top line of the shape is the amount of water the crop would use under ideal conditions on the associated day. This example shows a 0, 10, 20, 30, and 40% deficit occurring in stages 1 to 5 respectively, representing a 78% water use across the entire growing season as compared to ideal conditions. Understanding both the amount of water used and when the water was used, we are able to determine the associated yield, for this example, we reach 68% of potential yield.

Now, what if we were to simulate the yield using all reasonable water uses and all reasonable distributions of the timing of this water use? The resulting shape is our crop kite, with each point associated with a water use distributed throughout the growing season in a particular way:

 

This shape illustrates the incredible range of yields associated with each water use; for example, 80% of potential water use relates to between ~20 and 90% of potential crop yield.

Water distributed through canals are often delivered according to a schedule, and not necessarily related to growth-stage sensitivities or actual weather. From the crop kite we can derive estimates on how the crop yield will be affected by adopting certain irrigation schedules. We elaborate on this with three examples: S1) water use is distributed to optimize yield, S2) the deficit is distributed evenly across all growth stages, S3) water is used preferentially for the earlier growth stages. The resulting crop-water production functions are illustrated in the following figure:

 

Although the first schedule optimizing for crop yield may be in line with the motivations of the irrigating farmer, it is often an unreasonable assumption for farmers delivered water according to predetermined schedules, but may be appropriate for farmers irrigating with a privately owned well. Evaluating the potential of supplemental irrigation necessitates estimating the ability of farmers to manage both the amount and timing of irrigation applications. Otherwise, non-reasonable assumptions may be used to evaluate and over promise estimates for agricultural production, with the fault not in the practice of limited irrigation, but in the criteria used to evaluate the system.

Crop kites demonstrate the wide range of water use-crop yield relationships, and can be used to evaluate the potential of limited irrigation to shift both food and water security.

 

Mikhail Smilovic is a PhD candidate at McGill University and the University of Victoria . Mikhail’s work investigates the interplay between foot security, water resources, and energy, and evaluating and integrating initiatives that increase agricultural production while reducing demands on water resources.

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…

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

Socio-hydrogeology: bridging the gap between science and society

Socio-hydrogeology: bridging the gap between science and society

Authored by Viviana Re, Marie Curie Research Fellow at Ca’ Foscari University of Venice, Italy


Sustainability, integrated water resources management, climate change, groundwater governance. These are some of the currently trending topics in hydrogeology, as reflected by their widespread use as keywords in recently published literature. Indeed, hydrogeologists are at the forefront of guaranteeing the long-term sustainability of aquifers worldwide. But how can they assure that the outcomes of their investigations are really translated into effective science-based management practices? How can they make sure that their work really reaches water end-users and all those eventually affected by new water quality and quantity control measures?

Possibly the most effective way is to commit themselves to bridging gaps between science and society.

This is the aim of “socio-hydrogeology”, a new approach to groundwater investigations promoting the incorporation of the social dimension into hydrogeological studies willing to provide management practices with better support (Re, 2015).

Socio-hydrogeology proposes the coupling of robust hydrogeological investigations with a more comprehensive assessment of the socio-economic implications of the (ground)water problems in question. In agreement with the general definition of socio-hydrology—the science of people and water (Sivapalan et al. 2011)—socio-hydrogeology aims not only at studying the mutual relations between people and groundwater (i.e. the impact of human activities on the baseline characteristics of an aquifer and the impact of groundwater—its quality, its presence and scarcity—on human well-being and life), but more generally to include social dimensions in hydrogeological investigations. This means ensuring that the results of scientific investigations are not only based on real needs and local knowledge, but are also adequately disseminated to groundwater users .

Hydrogeologists can be leaders in socio-hydrogeology. They can advocate for groundwater management and protection. They can promote bottom-up approaches that embed local know-how into management strategies. As many hydrogeologists spend substantial time in the field, they are generally the first point of contact for well holders, farmers and other groundwater users. They may therefore act as mediators between theory and practice, or between the problem and the (potential) proposed solution to issues of sustainability and pollution. This is why allocating specific time to structured interaction with the relevant stakeholders and water users prior to and during hydrogeological investigations, they can maximize the use of hydrogeological information and outcomes, which are obtained, in the best cases, with the best available technology and tools.

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Socio-hydrogeology in practice:  in situ measurements and interviews with farmers (Cap Bon, Tunisia; Viviana Re, 2014)

This newly established field allows hydrogeologists to focus on mutual relations between groundwater and society and to foster both ‘horizontal’ (e.g. between state and non-state actors or across sectors such as agriculture or energy) and ‘vertical’ (between various levels) cooperation. This novel approach presents a standardized baseline method focused around hydrogeologists, which is easy to understand, flexible, not too time-consuming, and offers the chance to implement preliminary public engagement with limited effort.

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Discussions about water issues with farmers near Grombalia, Tunisia (Viviana Re, 2014).

In this framework, the Bir Al-Nas (Bottom-up IntegRated Approach for sustainabLe grouNdwater mAnagement in rural areaS*) approach is proposed as an initial attempt to put the concept of socio-hydrogeology into practice through hydrogeological and social analysis, the latter performed by means of a social network analysis and structured interviews with the people involved in the groundwater monitoring network. Bir Al-Nas is currently being tested and implemented in the Grombalia Basin (Tunisia), chosen as representative of the issues shared by most of the coastal aquifers in arid/semi-arid regions (i.e., aquifer pollution and salinization, water overexploitation, saline-water intrusion, and agricultural return flow).


*Research supported by a Marie Curie International Outgoing Fellowship within the EU 7th Framework Programme for Research and Technological Development (FP7-PEOPLE-2012-IOF, project reference 327287).

 –Featured image by Chiara Tringali (2014)

Brackish groundwater resources: is development advisable?

Brackish groundwater resources: is development advisable?

Authored by: Grant Ferguson – Assistant Professor in the Department of Civil & Geological Engineering at the University Saskatchewan


Groundwater makes up a large fraction of the Earth’s freshwater but that represents only a part of groundwater resources. Large volumes of groundwater are saline, with some reaching salinities of over ten times that of seawater. Brackish water is an intriguing part of the spectrum of groundwater resources, sitting just beyond the water quality salinity requirements for potable water. Many water scarce regions are considering the use of brackish groundwater, sometimes as a potable water resource via desalination or for industrial use where quality requirements are less restrictive. Recent studies by International Groundwater Resources Assessment Centre and the United States Geological Survey showed that these resources are relatively accessible in many areas around the globe.  For example, significant brackish groundwater is present at less than 500 feet below ground surface throughout most of the Great Plains.

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Distribution of saline groundwater resources in the contiguous United States. (image source).

Using brackish water certainly increases the amount of groundwater in storage that is usable, however what remains unclear is how this fits into the construct of groundwater management. Following ideas promoted by John Bredehoeft, pumped groundwater must be balanced by either an increase in recharge, a decrease in discharge or reduction of storage.  Typically, brackish water systems do not receive large amounts of recharge, nor are they well connected to surface water bodies. This suggests that most brackish water developments are mainly supported by withdrawal of water from storage and that the development of brackish water resources at large scales over longer time frames will result in groundwater depletion problems.

Given this possibility, is development of brackish groundwater resources advisable?

Possibly.

Some situations — such as auxiliary water supplies used during times of drought or high demand, and perhaps most notably for some regions, oil and gas development — only demand groundwater supplies for finite duration — for periods of months to a few years.  Both the Province of Alberta and the Canadian Association of Petroleum Producers have recently promoted such initiatives in oil and gas producing regions in Canada. However, the oil and gas industry has been using brackish and saline water in Canada for several decades.  During the 1970s, a few wells, installed across a small area in Saskatchewan and the Judith River Formation, pumped brackish water at high rates before they had to be abandoned due to excessive water table drawdown.  Other wells in the area have been used more or less continuously for the last few decades to support enhanced oil recovery, where water levels have not dropped to the point that these wells also need to be abandoned.  Simulations suggest that hydraulic heads have decreased by a few meters across distances of several kilometers from these pumping wells, however this regional drawdown has not been well documented (due a lack of monitoring) nor have water levels in the hundreds of wells in the shallow groundwater systems above Judith River Formation declined noticeably.

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

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.

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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.

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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.

fig3

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)

bonus2

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).

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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.

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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 ~

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