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What is the difference between ‘water withdrawal’ and ‘water consumption’, and why do we need to know?

What is the difference between ‘water withdrawal’ and ‘water consumption’, and why do we need to know?

Post by Inge de Graaf, postdoctoral researcher at the University of Freiburg, Environmental Hydrological Systems group

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Last week I had to teach my first class in global hydrology. When I showed the global trend on increasing demands and withdrawals (see Figure) I needed to explain the different terms as sometimes the term “water use” gets, well, misused.

The term “water use” often fails to adequately describe what happens to the water. So I told the students; if you see or hear to term ‘water use’ always ask yourself what’s actually being said. The term is often used for water withdrawals or water consumption, and it’s important to understand the difference.

Water withdrawal describes the total amount of water withdrawn from a surface water or groundwater source. Measurements of this withdrawn water help evaluate demands from domestic, industrial and agricultural users.

Water consumption is the portion of the withdrawn water permanently lost from its source. This water is no longer available because it evaporated, got transpired or used by plants, or was consumed by people or livestock. Irrigation is by far the largest water consumer. Globally irrigated agriculture accounts for 70% of the total water used and almost 50% is lost either by evaporation or transpiration.

Understanding both water withdrawal and consumption is critical to properly evaluate water stress. Measurements of water withdrawal indicate the level of competition and dependence on water resources. Water consumption estimates help to quantify the impact of water withdrawals on downstream availabilities and are essential to evaluate water shortage and scarcity. For example, most water used by households is not consumed and flows back as return flow and can be reused further downstream. However, water is rarely returned to watershed after being used by households or industry without changing the water quality, increasing water stress levels.

Already more than 1.4 billion people live in areas where the withdrawal of water exceeds recharge rates. In the coming decades global population is expected to increase from 7.3 billion now, to 9.7 billion by 2050 (UN estimate). This growth, along with rising incomes in developing countries, is driving up global food demands. With food production estimated to increase by at least 60% (FAO estimate), predicting water withdrawal and consumption is critically important for identifying areas that are at risk of water scarcity and where water use is unsustainable and competition amongst users exist.

Global trend I showed in my class, published in Wada et al (2016).

Ref:

Wada, Y., I. E. M. de Graaf, and L. P. H. van Beek (2016), High-resolution modeling of human and climate impacts on global water resources, J. Adv. Model. Earth Syst., 8, 735–763, doi:10.1002/2015MS000618.

 

How prehistoric water pit stops may have driven human evolution

How prehistoric water pit stops may have driven human evolution

Post by Matthew Robert Bennett, Bournemouth University and Mark O Cuthbert, Cardiff University

Our ancient ancestors seem to have survived some pretty harsh arid spells in East Africa’s Rift Valley over five million years. Quite how they kept going has long been a mystery, given the lack of water to drink. Now, new research shows that they may have been able to survive on a small networks of springs.

The study from our inter-disciplinary research team, published in Nature Communications, illustrates that groundwater springs may have been far more important as a driver of human evolution in Africa than previously thought.

Great rift valley.Redgeographics, CC BY-SA

The study focuses on water in the Rift Valley. This area – a continuous geographic trench that runs from Ethiopia to Mozambique – is also known as the “cradle of humanity”.

Here, our ancestors evolved over a period of about five million years. Throughout this time, rainfall was affected by the African monsoon, which strengthened and weakened on a 23,000-year cycle. During intense periods of aridity, monsoon rains would have been light and drinking water in short supply. So how did our ancestors survive such extremes?

Previously, scientists had assumed that the evolution and dispersal of our ancestors in the region was solely dependent on climate shifts changing patterns of vegetation (food) and water (rivers and lakes). However, the details are blurry – especially when it comes to the role of groundwater (springs).

We decided to find out just how important springs were. Our starting point was to identify springs in the region to map how groundwater distribution varies with climate. We are not talking about small, babbling springs here, but large outflows of groundwater. These are buffered against climate change as their distribution is controlled by geology – the underlying rocks can store rainwater and transfer it slowly to the springs.

The lakes of the African Rift Valley.SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

We figured that our ancestors could have stayed close to such groundwater in dry times – playing a greater part in their survival than previously thought. When the climate got increasingly wet, groundwater levels would have risen and made springs more plentiful – feeding smaller rivers and leading to lakes becoming less saline. At this point, our ancestors would have roamed across the landscape free of concerns about water.

Life and death decisions

To test this idea, we embarked on a computer experiment. If the springs and water bodies are thought of as the rest stops, or service stations, then the linkages between can be modelled by computers. Our model was based on what decisions individuals would have taken to survive – and what collective behaviours could have emerged from thousands of such decisions.

Individuals were give a simple task: to find a new source of water within three days of travel. Three days is the time that a modern human and, by inference, our ancestors could go without drinking water. The harder and rougher the terrain, the shorter the distance one can travel in those vital three days.

We used the present landscape and existing water springs to map potential routes. The detailed location of springs may have changed over time but the principles hold. If our agent failed to find water within three days, he or she would die. In this way we could map out the migration pathways between different water sources as they varied through 23,000-year climate cycles. The map shows that there were indeed small networks of springs available even during the driest of intervals. These would have been vital for the survival or our ancestors.

The model also reveals movement patterns that are somewhat counter-intuitive. One would assume that the easiest route would be along the north to south axis of the rift valley. In this way, hominins could stay at the bottom of the valley rather than crossing the high rift walls. But the model suggests that in intermediate states between wet and dry, groups of people may have preferred to go from east to west across the rift valley. This is because springs on the rift floor and sides link to large rivers on the rift flanks. This is important as it helps explain how our ancestors spread away from the rift valley. Indeed, what we are beginning to see is a network of walking highways that develop as our ancestors moved across Africa.

Mapping human migration.

Human movement allows the flow of gossip, know-how and genes. Even in modern times, the water-cooler is often the fount of all knowledge and the start of many budding friendships. The same may have been true in ancient Africa and the patterns of mobility and their variability through a climate cycle will have had a profound impact on breeding and technology.

This suggests that population growth, genetics, implications for survival and dispersal of human life across Africa can all potentially be predicted and modelled using water as the key – helping us to uncover human history. The next step will be to compare our model of human movement with real archaeological evidence of how humans actually moved when the climate changed.

So next time you complain about not finding your favourite brand of bottled spring water in the shop, spare a thought for our ancestors who may died in their quest to find a rare, secluded spring in the arid African landscape.

The ConversationThis research was carried out in partnership with our colleagues Tom Gleeson, Sally Reynolds, Adrian Newton, Cormac McCormack and Gail Ashley.

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Mark O Cuthbert, Research Fellow in Groundwater Science, Cardiff University

This article was originally published on The Conversation. Read the original article.

Fire and groundwater

Fire and groundwater

Post by Andy Baker, University of New South Wales

The effects of fire on the surface environment are clear to see. Landscapes are coated in ash. Intense fires can destroy all vegetation and alter soil properties. Less intense fires destroy just the surface leaf litter, grasses and shrubs.  Grass fires can be fast moving, destroying buildings and threatening lives. Intense fires can even form their own local weather systems.

But what about the effects of fire on water underground? Let’s think about what happens on the surface, and translate that to what is likely to happen to the subsurface.

Firstly, ash is burnt vegetation. It is rich in carbon, nutrients and trace metals, and can be mobilised after heavy rainfall. Heavy rainfall events are most likely to cause groundwater recharge as some of the rainfall makes its way down to the replenish the water table. As this happens we should also expect nutrients and carbon to be moved downwards towards the water table, as well as horizontally to rivers.

Secondly, where a fire destroys tree cover, then the canopy shading will be lost. We would predict hotter surface temperatures. This could alter the water balance, changing evaporation and also the amount or timing of groundwater recharge.

Finally, we would expect increased sediment movement. This could block flow routes to the subsurface, such as fractures and sinkholes. This would change the routes by which water moves from the surface to the water table.

Of course, the problem with water underground is that it is hard to see and measure. So how can we observe the effects of fire in the subsurface? We have been using caves in karstified limestone as a way to sample the water as it moves from the surface to the groundwater.

In caves, you can monitor the water chemistry and hydrology after a wildfire. If you know when a fire will occur, you can make measurements before and after. And you can investigate the chemical record of past fires preserved in cave stalagmites.

What do we see from the cave? We see increased evaporation and decreased recharge in the years immediately after  an intense wildfire. We see nutrient flushes from the surface to the subsurface, moderated by vegetation uptake as regrowth occurs. And we have started to compare the stalagmite geochemical signals of fire, cyclones and global warming.

We are starting to understand a little bit about the effects of fire on water as it moves through the unsaturated zone of limestone. What about other rock types? What about the groundwater aquifer itself? We need to know more about the effect of wildfires on our subsurface water resource.  The fire season is getting longer. A greater extent of the earth’s surface is being burnt. Both will continue to increase with global warming, but how will this affect the water underground?

image source

Squeezed by gravity: how tides affect the groundwater under our feet

Squeezed by gravity: how tides affect the groundwater under our feet

Post from the Conversation, by Gabriel C Rau, Ian Acworth, Landon J.S. Halloran, Mark O Cuthbert

When returning from a swim in the ocean, sometimes it seems as though your towel has moved. Of course, it’s just that the water line has shifted.

The natural rise and fall of the ocean at the beach is an excellent demonstration of gravitational forces exerted by the Sun and the Moon. Although the tidal force is small, it is strong enough to pull regularly on the ocean, making an enormous volume of water rise and fall.

What you might not know is that tidal forces from the Sun and Moon also influence the air we breathe and the solid ground we stand on. These effects are referred to as atmospheric and Earth tides.

While we don’t tend to notice Earth and atmospheric tides, they do affect both the land and the world’s largest freshwater resource located underneath our feet: groundwater. This occupies the pores that exist in geological materials such as sand or soil, much like water in a kitchen sponge.

We have developed a method that incorporates tidal influences to monitor our precious groundwater resources without the need for pumping, drilling or coring.

Water beneath our feet

It has been estimated that groundwater makes up 99% of the usable freshwater on Earth. If all of Earth’s groundwater were extracted and pooled across the world’s land surface, it would be enough to create a lake 180 metres deep.

While this sounds like a lot of water, it is important to remember that not all groundwater is available for use. In fact, groundwater is currently mined on a global scale, especially in drier parts of the world, where groundwater underpins human activities during times of drought.

Groundwater extraction can lead to a downward shift in the land surface level (known as “subsidence”), particularly if groundwater is removed from underground zones that contain soft clays. This is a significant global problem, especially in coastal areas, due to urbanisation and associated water demand.

Alternatively, a long wet period with excess rainfall can cause the groundwater to rise up and cause flooding.

Effect of tides on groundwater

Deeper groundwater buried underneath layers of different types of sediments is under great pressure (in groundwater terminology this is called “confined”). The gravity change from Earth tides squeezes the sediment, and therefore changes the pressure of the water in the pores.

The atmospheric tides add to the weight that is sitting on top of the groundwater and cause a change in stress that results in a downward squeezing.

Groundwater at that depth responds to these stress changes, which can be measured as tiny water level fluctuations inside a groundwater borehole.

We have developed a new approach that exploits these tidal influences to calculate important subsurface properties. For example, this can predict how the pressure is lowered when groundwater is pumped, and by how much the land surface would sink as a result of shrinking subsurface material (just like squeezing a kitchen sponge).

The method basically allows accurate calculation of the compressible subsurface properties from the groundwater response to Earth and atmospheric tides.

This development is significant because it will allow analyses of a subsurface water reservoir (called an aquifer) without human-induced stresses such as pumping or taking physical samples of the material through drilling or coring in addition to constructing a borehole.

All that’s needed for this analysis is a roughly 16-day period of continuous measurements of groundwater levels and atmospheric pressure at hourly intervals.

Groundwater levels are routinely recorded as part of water monitoring programs around the world and in Australia, as funded by the Federal Government groundwater NCRIS scheme. Atmospheric pressure is a standard parameter measured by weather stations, such as operated by the Bureau of Meteorology.

The effects of tidal forces on groundwater might be less apparent to us than their effects on the ocean, but they’re just as important. Our new method of understanding the influence of tides on groundwater significantly reduces the effort to predict the response to groundwater pumping and the potential for land subsidence.

This technique can make passive use of existing boreholes and could be applied to the global archive of groundwater levels to inform more sustainable groundwater resource development in the future.

Monitoring groundwater drought without measuring it

Monitoring groundwater drought without measuring it

Post by Anne van Loon, University of Birmingham

You might remember that the summer of 2015 was extremely dry in large parts of Europe (Figure 1), leading to crop losses, wildfires, drinking water supply deficiencies, and reductions in energy production and navigation (Van Lanen et al., 2016), whether you experienced it yourself or read about it in the newspapers. Based on incomplete information the European Environment Agency already estimates the total economic losses of the event at more than 2 billion Euros (http://www.eea.europa.eu/data-and-maps/indicators/direct-losses-from-weather-disasters-3/assessment).

Figure 1: Media coverage of the 2015 drought in Europe (source: The Guardian)

Seventy-five percent of EU inhabitants depend on groundwater for their water supply, which makes groundwater management extremely important. To manage groundwater effectively during drought periods like 2015, data about groundwater levels are needed in (near-) real time. However, observations of groundwater levels are rarely available in real time, even in Europe, one of the most densely monitored areas of the world.

In a just published paper, we therefore tested two methods to estimate groundwater drought in near-real time (Van Loon et al., 2017). The first method is based on satellite data from the GRACE satellites (Gravity Recovery and Climate Experiment, grace.jpl.nasa.gov), a cool new pair of satellites that measure the Earth’s gravitational field to estimate changes in the amount of water on Earth. Previous research had suggested that the Total Water Storage (TWS) anomalies derived from GRACE could represent hydrological drought (e.g. Thomas et al., 2014). With models the TWS anomalies can be decomposed into their compartments, including groundwater storage. The second method uses a statistical relationship between rainfall and historic groundwater levels, which depends on aquifer properties and has previously been used to study past drought events (e.g. Bloomfield and Marchant, 2013).

To test both methods we looked at the benchmark 2003 drought for two regions in southern Germany and eastern Netherlands. First, we used observed groundwater level data from 2040 monitoring wells to calculate the Standardized Groundwater Index (SGI), which ranges from 0 (abnormally dry) to 1 (abnormally wet) (Figure 2a). Interestingly, the SGI reveals the patchiness of the 2003 groundwater drought caused by differences in aquifer characteristics. Quickly responding aquifer systems experienced drought in response to low rainfall in previous months and slowly responding aquifer systems experienced wetness in response to high rainfall in the preceding year (you might be aware of the 2002 summer floods in the same region). GRACE TWS showed dry anomalies in Germany and (to a lesser extent) in the Netherlands (Figure 2b), but the coarse resolution of GRACE prevents it from picking up the high spatial variability in groundwater levels we saw in the observations (Figure 2a). The groundwater storage derived from GRACE TWS by subtracting surface and soil storage gave abnormally wet conditions in most parts of the study regions (Figure 2c), with drier than normal values only in the eastern part of Germany which in the observations was mostly wetter than normal (Figure 2a). Finally, we calculated a form of the SGI based on the response of groundwater to precipitation (Figure 2d). The spatial pattern of this precipitation-based SGI closely resembles the observed SGI (Figure 2a), although it slightly overestimates the severity of the groundwater drought in Germany.

Figure 2: The 2003 groundwater drought in southern Germany and eastern Netherlands, derived from a) observed groundwater levels (standardised groundwater index, SGI), b) GRACE Total Water Storage (anomalies with regard to the long-term average), c) groundwater anomalies based on GRACE and model outputs (anomalies with regard to the long-term average), and d) observed precipitation and the relationship between precipitation and groundwater levels based on historic data (standardised groundwater index, SGI). Adapted from Van Loon et al. (2017).

We then used the precipitation-based SGI to estimate the 2015 groundwater drought in the same regions (Figure 3). This showed a completely different picture than the 2003 drought. Almost the whole region of southern Germany experienced an extreme drought, whereas the Netherlands was quite wet in August 2015. No patchiness in groundwater levels was observed in 2015, because both short- and long-term rainfall were below average. This means that the 2015 drought was more severe in terms of water resources for drinking water and irrigation because all groundwater wells had low levels, compared to about two thirds in 2003.

Figure 3: The 2015 groundwater drought in southern Germany and eastern Netherlands, derived from observed precipitation and the relationship between precipitation and groundwater levels based on historic data (standardised groundwater index, SGI). Adapted from Van Loon et al. (2017).

Based on our analysis, we think that using readily available rainfall data and the historic relationship between rainfall and groundwater is a cunning way to monitor groundwater drought at a high enough resolution for water management. However, this technique still has more uncertainties than using real-time groundwater observations directly. To prevent issues with drinking water supply for the EU’s 380 million people that depend on groundwater, there is a clear need to measure groundwater levels and make them freely available in real-time.

The scientific paper on which this blog is based can be found here (http://www.hydrol-earth-syst-sci.net/21/1947/2017/).

References

Bloomfield, J. P. and Marchant, B. P. (2013) Analysis of groundwater drought building on the standardised precipitation index approach, Hydrology and Earth System Sciences, 17, 4769–4787, doi: 10.5194/hess-17-4769-2013.

Thomas, A. C., Reager, J. T., Famiglietti, J. S., and Rodell, M. (2014) A GRACE-based water storage deficit approach for hydrological drought characterization, Geophysical Research Letters, 41, 1537–1545, doi: 10.1002/2014GL059323.

Van Lanen, H. A. et al (2016) Hydrology needed to manage droughts: the 2015 European case. Hydrological Processes, 30: 3097–3104. doi: 10.1002/hyp.10838.

Van Loon, A. F., Kumar, R., and Mishra, V. (2017) Testing the use of standardised indices and GRACE satellite data to estimate the European 2015 groundwater drought in near-real time, Hydrology and Earth System Sciences, 21, 1–25, doi: 10.5194/hess-21-1-2017.

 

Musical groundwater?

Musical groundwater?

Post by Kevin Befus, University of Wyoming

I don’t mean to get your hopes up, but keep them up there. I’m not talking about recording the sonorific excitement that is groundwater flow. And, I’m not talking about the squeak of a pump handle, the gurgling of a spring, the grumble of a generator, or the roar of a drill rig. Rather, I want to share with you some songs that reference groundwater in one capacity or another, though references to specific capacity have yet to be found. Groundwater might not be photogenic …more discussion to follow, but is it musical?

For the last couple of years, I have been amassing a playlist of songs that reference water (well, ever since I discovered how perfect “Once in a Lifetime” by the Talking Heads was for motivating me during graduate school…in my opinion, there is no better song to listen to before hitting submit on that manuscript or grant for good scientific mojo). Sifting through a couple hundred songs that sometimes only marginally use water to metaphorize the human condition, I have honed the list to an ordered version of what I consider “The best/only groundwater songs”:

1) Once in a lifetime – Talking Heads
See previous post for a thorough run down

2) Water of Love – Dire Straits
A yearning for water/love, deep underground and hard to find. Let’s hope for some recharge to elevate the water table and maybe even support the river’s running free.

3) Cold Water – Old Time Relijun
Warning, this song is different, but it is about groundwater and wonderfully so. “Cold water going down…through the roots, through the mud, through the rocks, through the ground, through the sand, through the Earth and all the land”. Talk about groundwater flow and potential recharge! It’s also cold, fitting the gross expectation that groundwater near recharge areas is cooler (in regional flow systems at least) than further along the flow system.

4) I am a River – Foo Fighters
They find a groundwater system that thinks it is a river beneath a subway floor…a classic case of mistaken identity.

5) Hallelujah Band – Eilen Jewell
“I climbed down underground
to listen for a new sound
found a river underneath our feet
dark and silent, deep”

Sounds like a quiet unconfined karst groundwater system to me.

6) You Don’t Miss Your Water – Otis Redding

7) Cool Water – Sons of the Pioneers (later sung by Johnny Cash, Joni Mitchell, and others)

8) Water in a Well – Sturgill Simpson

9) Water – Jack Garratt

10) Our Lady of the Well – Jackson Browne

11) Crow Jane – Skip James (also Derek Trucks Band)

12) Well Run Dry – Phat Phunktion

My musical explorations have taught me love is like water. Groundwater? Maybe, depends on its amount, depth, and quality. Wells can be the source of good and bad waters, and we can have some say on whether it’s one or the other. These songs and others (that don’t reference groundwater specifically) bemoan or extol love/water, which comes or goes and can be so uncontrollable.

Groundwater can also be a source of contemplation. Water underground is often interpreted as “silent” (in both “Hallelujah Band” and “Once in a Lifetime”), but springs are allowed to burble and gurgle. So long as we have saturated conditions in a simple single-porosity system, I would bet the groundwater flow is generally difficult to hear. But remember, groundwater is under pressure (atmospheric, hydrostatic, or otherwise) and “wants” to break free (Queen references…couldn’t help myself), especially when in confined aquifers.

There is at least one more way groundwater systems can invoke contemplation. Back before powered pumps, drawing water from a well took time, and that time could be used to think through the triumphs and trials of life. Maybe that’s one reason why groundwater hydrologists are often excited to get into the field.

Quick aside, San Diego has recently started a music festival called GROUNDWATER, where modern house music is the theme. I have not yet sifted through their performers’ lyrics in search of water references, but I would gladly take your help. Words may be in low concentrations.

Join my musical adventures in groundwater and share your finds with us in the comments below!

For your hydrogeological musical pleasure:

feature image: IAH Netherlands Chapter

Of Karst! – short episodes about karst

Of Karst! – short episodes about karst

Episode 1 – A different introduction to karst

by Andreas Hartmann Lecturer in Hydrology at the University of Freiburg

Usually, textbooks or lectures start with the theoretical background and basic knowledge of the topic they try to cover. Writing my first contribution to the Water Underground blog I want to take advantage of this less formal environment. I will introduce karst as I and many others around the world see it. As the most beautiful environment to explore and study.

Some of you may not be familiar with the term karst, its geomorphology or hydrological consequences. But I am almost certain that most of you have seen the landforms in the four pictures below.

Tower karst (1st photo) is typical of tropical regions. The picture below is taken close to Guilin, Southwest China, and I am sure many of you remember James Bond “The Man with the Golden Gun” and the beautiful tower karst islands at which parts of movie takes place (episode 3 will be a special feature about karst in the movies). Tower karst reaches heights up to 300m and often referred to by its Chinese name Fenglin or Fengcong karst, when occurring in a large number.

The 2nd photo shows the opposite landform: a huge hole in the forest ground. This is not a crater but a very big collapse sinkhole at Vermillion Creek, Northwest territories, Canada. It has an ellipse shape (60m x 120m) and 40 m below the surface, it has a lake whose depth has not yet been determined. You may not have previously heard the term sinkhole. But on the news one day you will hear stories of holes suddenly swallowing cars or entire houses in Florida or Mexico. If not due to mining, those were most probably collapses that occurred due to karstification.

Figure 1: (1) amazing tower karst Li River, Gulin, China (duskyswondersite.com), (2) collapse sinkhole , Vermillion Creek, Northwest territories, Canada (pinterest.com), (3) Kalisuci Cave at Jogjakarta, Indonesia (ourtheholiday.blogspot.com), (4) spring of the Loue River, France (wikiwand.com)

The most popular features of karst are caves, some of them as large as entire buildings. The 3rd photo shows how it may look inside a karstic cave (Kalisuci Cave at Jogjakarta, Indonesia). Note that there are plenty of stalactites and that there is a lot of water that will eventually find its way back to the surface discharging a karstic spring.

The 4th photo shows the spring of the Loue River, France, which is one of the largest springs in Europe. The volumes of water coming out easily compare to the discharge of medium size rivers. If you ever saw a spring that big it must have been a karst spring!

In the Of Karst! series, I will take you on a journey through more of these amazing characteristics of karst. I will show how its evolution over time can produce the landforms shown here. I will show how karstification affects the resulting movement of water on the surface, in caves systems and in karstic rock. And I will explain why karst is so relevant for our societies. In episode 2 (late June 2017) I will speak of how karst evolves. Episode 3 (early October 2017) will a special feature about karst in James Bond other famous movies.

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

Research mini-conference in fourth year groundwater class

Research mini-conference in fourth year groundwater class

Fourth year and graduate students led a fun mini-conference during class in Groundwater Hydrology (CIVE 445, Civil Engineering at University of Victoria) yesterday. Local consulting and government hydrogeologists joined, making the students both nervous and excited to be presenting to professionals with up to forty years of groundwater experience. The presentations were the culmination of a term-long independent group research project – they also write a research paper (which is peer-reviewed by their classmates). And the mini-conference culminated in beers at the grad club, unfortunately drinking beer brewed with surface water.

It seemed like a win-win-win for everyone. The students loved meeting and presenting to, and being grilled by, the people who had mapped the aquifer they were modeling or asked if their model is based on any real data. The practitioners loved seeing the new ideas and enthusiasm of the students. And I loved seeing the interaction and learning.

For any prof reading this, here is a description of the Group Research Project and the conference poster:

 

 

 

 

 

WTF of the WTF method

WTF of the WTF method

by Tara Forstner, University of Victoria

I recently wrote a term paper for one of my graduate classes on the limitations of the water table fluctuation (WTF) method, and I have to say, WTF!

Techniques using groundwater level fluctuations as a means of calculating recharge are very common. With observation well hydrographs and precipitation data, this method can be applied quite simply, requiring no field work or data collection. Although, this is definitely not the method to end all recharge methods for a number of reasons. As a newbie hydrogeologist studying the WTF method, the application of the method quickly became convoluted based on its limitations and uncertainties.

My term paper focused mainly on the WTF method as described by the classic papers by Healy and Cook (2001), and Cuthbert’s novel estimation of drainage (Cuthbert, 2010) and straight line recession (Cuthbert, 2014).  Here is a list of the three most important things I learned:

  • Developing a good conceptual model of the region is essential for the success of this method, as large uncertainties entail if effects of pumping, proximity to surface water bodies, water table depths, and geology are not considered. With the water table fluctuating based on several factors, it becomes essential to investigate possible influences.
  • The WTF method has two main approaches; (a) to solve for a time series model of recharge, or alternatively, (b) to calculate a long term average recharge value from the groundwater recession constant. The time series approach is best used to observe fluctuations of recharge in response to precipitation over a smaller temporal scale compared to the long term average recharge value calculated from the groundwater recession constant.
  • Simply ‘plugging in’ the values or using computer programs to estimate drainage recession constant could seriously warp the ‘real’ recharge value. Mark Cuthbert mentioned to me in a discussion that he still prints off the hydrographs and often plots the groundwater recession by hand in order to help visualize the groundwater recession before taking a computing approach.

In closing I thought I would share one of my silly ‘WTF!?’ moments and that ‘oooooohhh’ moment that follows once I figured it out. In Healy and Cook (2002), the formula for recharge is written as R = Sy dh/dt, and later in Crosbie (2005) as R = Dh Sy and Cuthbert (2010) as R = Sy dh/dt + D. There are two things that tripped me up with this method. Firstly, the meaning of the symbols R and Dh varies slightly between papers which is easy to miss, and recharge is either calculated as a rate or a value over a specified time. Secondly, the approach in deriving the groundwater recession constant is also different in all three papers, and should be chosen on the basis of the conceptual model.

So alas, the WTF can definitely have it’s ‘WTF!?’ moments, however when the method, possibilities, and limitations are properly understood, this method has the potential of providing a cost effective and non-invasive approach in deriving recharge values.

Deep challenges: China’s ‘war on water pollution’ must tackle deep groundwater pollution pathways

Deep challenges: China’s ‘war on water pollution’ must tackle deep groundwater pollution pathways

by Matthew Currell, School of Engineering, RMIT University, Australia

As part of its recent ‘war on pollution’, the Chinese Central Government released a major policy on water pollution control and clean-up, called the ‘10-point water plan’ in 2015. The plan aims to deal once and for all with China’s chronic water quality problems. China’s water quality deficiencies became widely recognised around the turn of the millennium, following publication of seminal works by Ma Jun, Elizabeth Economy and other local and overseas environmental campaigners. It is now widely acknowledged that chronic exposure to water pollution in China has contributed to the emergence of hundreds of cancer villages, where rates of particular types of cancer that are linked to water pollution far exceed normal population-wide averages. In addition to agricultural pollution and domestic wastewater, in many regions the pollution has resulted from industries that are part of multi-national supply chains, meaning international factors have played an important role.

In a recent review paper published in Environmental Pollution, my colleague Dongmei Han and I compiled data from official Chinese government reports to provide a snapshot of the current status of water quality in China’s major river basins, coastal waters and groundwater systems, including shallow unconfined and deeper confined aquifers (Figure 1). The results are sobering, showing that despite some recent progress, about a third of China’s river monitoring stations and more than 60% of sampled groundwater wells are seriously polluted. These data agree with an internal Ministry of Water Resources report that was briefly made public in early 2016, which showed that more than 80% of the more than 2000 monitored shallow groundwater wells in northern China’s plains areas contain serious pollution and that the aquifers they monitor are unfit to supply drinking water.

Figure 1 – Status of water quality in China based on recent government statistics. a) Surface water, ranked according to the 6-class water quality classification standard. b) Groundwater, ranked using the 5-class system in 6 sub-areas of China, including shallow and deep groundwater. Overall percentages of sampled stations/wells in each water quality class are shown as large pie-charts; percentages in yellow and red on small pie-charts indicate proportion of samples in the lowest two classes (IV & V) for shallow and deep groundwater, respectively. Both maps have been overlain with the locations of known ‘cancer villages’.

In addition to the government data, we also targeted the research literature and compiled as many datasets as possible reporting concentrations of nitrate in shallow and/or deep aquifers throughout China. Compiling these data from over 70 different sources provides greater local detail about the severity of groundwater pollution (Figure 2). We chose nitrate as an ‘indicator pollutant’ because it is widely measured, easy to detect and highly water-soluble. The presence of nitrate in a sample is often an indicator that other pollutants may also be there. The results indicate that all shallow aquifers sampled contain nitrate above the typical natural background level (approximately 1 mg/L nitrate-N or 4.5 mg/L nitrate as NO3 ion), indicating some degree of pollution. Of these 36 aquifers, samples from 25 contained nitrate concentrations exceeding the US EPA maximum contaminant level (MCL) of 10 mg/L nitrate-N. Worryingly, all but one of 37 deep or karst aquifers examined contained nitrate above the background level, while 10 of these aquifers had samples above the MCL. In five of the shallow aquifers and four of the deep aquifers, median nitrate concentrations also exceeded the MCL, meaning half of all wells in the aquifer pump groundwater with nitrate levels exceeding the maximum safe level. We also compiled groundwater stable nitrogen isotope values of the nitrate where they were available. These isotope data help to identify the major sources of nitrate pollution such as chemical fertilizers, soil nitrogen, manure and domestic wastewater, as each potential source can have a unique isotope ‘signature’. Nitrogen isotopes can also provide evidence of microbes breaking down pollution; this is important when considering whether the nitrate will naturally degrade, or if engineered clean-up strategies are required.

Figure 2 – Nitrate concentrations in groundwater from major groundwater systems in China: a) Location map of the 52 study areas from which data were compiled; b) & c) Boxplot distributions of nitrate concentrations (as N) in shallow and deep groundwater throughout China. Boxplots show median, inter-quartile range and 10th and 90th percentile values. Data is compared to the United States Environmental Protection Agency maximum contaminant level (10 mg/L) and a background concentration of 1 mg/L Nitrate-N (equivalent to approximately 4.5 mg/L nitrate as NO3- ion).

Perhaps the issue of greatest concern from our review was the observation that in addition to being ubiquitous in shallow groundwater (as is perhaps expected in areas of intensive agriculture or wastewater pollution), nitrate pollution also frequently appears in deep wells (drilled to >100m below the surface) throughout China. Normally, the time taken for water to reach these confined aquifers is long, and much of the deep groundwater in China has been dated using radio-isotopes, which indicate that it was recharged thousands or tens of thousands of years before the present. The presence of nitrate above natural background levels in these groundwater bodies suggests that pollution is undergoing rapid ‘bypass flow’ (e.g. taking short-cuts) from the surface into deep aquifers.

The Chinese Ministry of Water Resources has made public statements indicating it believes that China’s deep aquifers are safe drinking water sources, isolated from surface pollution effects due to natural geological barriers (called ‘aquitards’ by hydrogeologists). However, our data call into question this assumption. A similar finding was recently made by a group at the Chinese Academy of Sciences, who conducted a geochemical survey of tap water from various sites around Beijing. Most of Beijing’s water supply plants pump from deep groundwater wells around the city. The survey found that a significant number of samples contained nitrate and other pollutants, consistent with our findings that contamination is reaching deep aquifers through short-cut pathways. The most likely explanation is that polluted water is flowing from shallow depths down preferential conduits, such as poorly constructed or badly maintained wells, and bypassing natural geological barriers (Figure 3).

It is estimated that over 4 million wells have been drilled in China’s northern plains alone since the groundwater boom of the 1960s and 1970s. However, only a fraction of these are registered with the government or maintained. Clearly, a program to identify and plug leaking and abandoned wells is needed to stop further pollution of China’s precious deep groundwater reserves.

 

Figure 3 – Mechanism by which faulty wells can allow shallow contaminants to bypass into deep aquifers, compromising water supply safety. China has millions of unregistered wells that may act in this way, and depends on deep aquifers for much of its drinking water.

We hope that our research highlights the scale of China’s water pollution challenges, and can help the public and policy makers better understand the extent and mechanisms of groundwater pollution – a problem which is causing serious human health effects. While addressing the problem of pollution in deep aquifers will be difficult, it is too important a task to ignore, as these aquifers supply drinking water to millions of Chinese people.

References & Further reading

Currell, M.J., Han, D., Chen, Z., Cartwright, I. (2012). Sustainability of groundwater usage in northern China: dependence on palaeowaters and effects on water quality, quantity and ecosystem health. Hydrological Processes 26: 4050-4066.

Currell, M.J., Han, D. (2017). The Global Drain: Why China’s water pollution problems should matter to the rest of the world. Environment: Science and Policy for Sustainable Development 59: 16-29. http://dx.doi.org/10.1080/00139157.2017.1252605

Han, D., Currell, M.J., Cao, G. (2016). Deep challenges for China’s war on water pollution. Environmental Pollution 218: 1222-1233. http://www.sciencedirect.com/science/article/pii/S0269749116310363

Peters, M., Guo Q., Strauss, H., Zhu, G. Geochemical and multiple stable isotope (N, O, S) investigation on tap and bottled water from Beijing, China. Journal of Geochemical Exploration 157: 36-51. http://www.sciencedirect.com/science/article/pii/S0375674215300030

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