Geology for Global Development

Geology for Global Development

Guest Blog: Anthropogenic climate change – what does this mean for groundwater resources in Africa?

Borehole in Tanzania (Credit: Tumaini Fund)

On the 25th October, Laura Hunt (Cardiff University) attended the joint meeting of the International Association of Hydrogeologists (IAH) and the Hydrogeological Group of the Geological Society, which included the Ineson Lecture at the Geological Society of London. 

It is a common misconception that Africa is an entirely dry, arid continent, parched for water. A resource that we in the UK take almost for granted, but that we assume all across Africa is hard to come by, with women walking many miles a day for drinking water, which is for the most part polluted with toxins and waterborne diseases. And for many communities, in many countries within Africa, this unfortunately is the case; the lack of surface water is a barrier to social and economic development.

But Africa is also a resource rich continent in terms of water. The continent has a huge groundwater resource, including large transnational aquifers. The exploitation of this incredible resource could be the key to facilitating Africa’s development, and coping with its rapidly increasing population.

Increasingly, investment in Africa’s water resources from NGOs, charities and private firms is in boreholes to extract clean groundwater. However, with anthropogenic driven climate change in this century and beyond predicted to be most adverse and rapid in the lowest (and highest) latitude regions, it’s important to understand the implication of a (overall) warmer and wetter world on this important resource prior to huge investment and increased dependency of many vulnerable countries upon it.

At the IAH conference, which I was lucky enough to attend with support from Geology for Global Development, University College London’s Richard Taylor spoke of his work aiming to answer this question with use of the ‘Chronicles Consortium’ – a collaboration of many groundwater resource’s multi-decadal hydrographs from a number of African countries to understand the response of aquifers to short term climatic events.

Africa is a vast continent with huge contrasts in climate between regions, and so climatic changes will not be unilateral across the continent, hence leading to different impacts on distant groundwater resources. The 2015/2016 El Nino event which was the second strongest event experienced for 150 years lead to contrasting impacts on the water balance across the continent. The Limpopo Basin (central southern Africa) experienced dry conditions, enhancing aridity in the area, whereas Northern Mozambique experienced wetter weather, with groundwater recharge recorded at 2000 boreholes.

The ENSO (El Nino Southern Osscilation) evidently had a strong influence upon groundwater recharge in some areas. In central Tanzania. Despite increased rates of pumping from the aquifers in the Makutapora basin (ie decline in water), ground water levels still rose.

The mechanism and conditions for recharge to occur is important in understanding the response of climatic change. Recharge velocities associated with the application of the regular diffuse model to recharge of the Makuapora Basin are simply inadequate to account for the rates of recharge recorded. However a mechanism of recharge focused pathways that focus diffuse recharge allow for faster infiltration and recharge of groundwater. These recharge pathways are the major, domain component of groundwater recharge as they are so focused compared to diffuse infiltration, but are only realised (utilised). Approximately 5-15mm of rain per day is required for 5-13 days are required for recharge to occur.

It can therefore be concluded that recharge occurs episodically and results disproportionately from heavy rainfall events.

So what are the implications of the changes in climate that we are already seeing and will continue into and beyond the 21st Century and beyond on these ground water resources? The key to sustainability is that development and investment should benefit future generations and so we need to make sure that this resource is viable for the future.

Firstly, climate change will lead to increased aridity around the equator, but enhanced rainfall around the tropics, creating disparity in the health of aquifers across the Africa.

Around the tropics, precipitation is expected to be less frequent but more intense, and so the threshold required for recharge is likely to be met, and so recharge will be greater (along with increased frequency of flooding events).

However, heavy rainfalls and increased macrogenic flow of water in the soil zone leads to greater contamination of shallow waters and are more vulnerable to pathogen transfer. Antecedant conditions also have a significant control over water quality with dry antecedent conditions leading to lower water quality with the highest degree of contaminiation than if antecedent conditions are wet. If climatic change causes more intense precipitation, and less gentle rainfall events, groundwater in regions of recharge are likely to become increasingly contaminated.

This research is just the beginning of understanding and predicting the response of the water table to climatic change, but allows us to begin to understand what challenges will be faced by Africa’s hydrogeologists and water authorities. This incredible resource with the power to drive Africa’s development, if chosen to be located in areas where overall long term recharge will occur, can be managed to reduce the effects of enhanced contamination and therefore provide a reliable and safe drinking water supply to some of the people most vulnerable to anthropogenic driven warming. With management of disease spread that was also showcased at the IAH conference by Cambridge University, it seems that there is the potential for a positive future for some African countries water resources to be revolutionised by the use of ground water. And this can be done sustainably – so long as the right long term management and planning, and of course further research is implemented.

This post is a guest contribution, sharing initial thoughts of a student attending the Ineson Lecture (and associated meeting) in London. For further information about the event, please see the event webpage and  contact the speakers directly.

Jesse Zondervan’s #GfGDPicks (Nov 2017): How did people in ancient times fare during climate changes? Should we use geoengineering? #SciComm

Each month, Jesse Zondervan picks his favourite posts from geoscience and development blogs/news, relevant to the work and interests of  Geology for Global Development . Here’s a round-up of Jesse’s selections for the past month:

How successful were people in the Neolithic and ancient times in adapting to climate change? Two contrasting stories emerged this month:

A new study from Past Global Changes (PAGES) suggests that abrupt shifts in climate caused by eruptions helped to trigger violent uprisings and other political upheaval in the Ptolemaic era. A more constructive message comes from the University of Plymouth, where researchers suggest we can learn from human behaviour during the last intense period of global warming.

Staying with the volcanic theme: David Bressan reports on the volcanic fatalities database published this month in the Journal of Applied Volcanology. What are the deadliest hazards associated with a volcano?

Further in the disaster risk reduction world, we see optical fibre strands underneath Stanford University used as an earthquake observatory. Meanwhile, earthquake apps bring more superpowers to your smartphone: learn how to use them in Andrew Alden’s post on the Oakland Geology blog.

I will finish with the question Anna Pujol-Mazzini poses: Could geoengineering the planet to curb climate change leave people in poor countries better – or worse – off?

A historical perspective:

Sustainable cities

Credit: Yanick Folly winner of the Sustainable Cities photo competition (http://tinyurl.com/y9jju98h)

Disaster Risk Reduction

Climate Change Adaptation

Opportunities

Check back next month for more picks!

Follow Jesse Zondervan @JesseZondervan. Follow us @Geo_Dev & Facebook.

Robert Emberson: Geomythology – Why understanding cultural traditions of landscape are important for sustainable development

Every culture has myths and legends about their native lands. Before we understood the geological forces that forced up great ranges of mountains or sculpted barren deserts, humans needed an explanation for the scale and majesty of natural phenomena. Stories of deities inhabiting volcanoes, or angry gods shaking the very ground upon which people lived, helped people make sense of disasters when tectonic forces were unimagined. Since the advent of the scientific method, and secularised science, such tales are often forgotten when we look at a landscape; why resort to a story when the facts say otherwise?

Devil’s Tower, Wyoming. Image courtesy psaudio / Pixabay

In some cases, it’s true that such stories don’t offer geologists much factual evidence about how the landscape formed. Even beautiful stories about features like the Devil’s Tower, in Wyoming, USA; the ancestral tale tells of people pursued by a giant bear; once they had reached the top of the peak, the bear could not reach them, but the scratch marks on the sides were testament to its attempts. Today, we know these are classic examples of columnar jointing. Although we might enjoy the story, it definitely doesn’t tie to the more modern understanding!

But there are some instances where we should perhaps pay more attention to myths, and particularly in the context of geology and sustainable development. While the tangible evidence of geological processes are often visible at a grand scale, it’s also true that the signals or proxies we look for to understand these processes can be very scarce. Trace fossils, or small shifts in element abundances, for example; we should take advantage of every shred of evidence we can find. As a result, some scientists have been turning to ancestral stories – in particular those about catastrophic events – for information.

Researchers have found tantalising clues about past events in mythical tales, and it seems often there is no smoke without fire. Amongst other studies, geologists have found evidence of volcanism in previously thought-dormant Pacific Volcanoes from local accounts, and evidence of giant floods in China, partly linked to tales of Emperor Yu 4000 years ago. The cultural memory of such giant catastrophes is etched into the myths told there; it seems that using these stories could help us better establish the timing and recurrence of natural disasters, allowing for improved risk analysis and development in tune with natural events.

There’s another, perhaps even more important aspect of geological myths to bear in mind for sustainable development. It’s increasingly well understood that the best approaches taken to encourage development, economic or otherwise, will differ across the world, driven by cultural differences. Development anthropologists could point to studies (e.g. see here) indicating that the definition of quality of life varies widely to suggest that a local approach would be the most sensible in approaching development, rather than assuming a standard ‘western’ approach would work everywhere.

The relationship of people to their landscape is, for the same reasons, an important variable to consider when discussing development. For example, Mt Machapuchare in Nepal is of special significance to Hindus, and as such is off-limits to climbers (and indeed has never been summitted). It is not the only mountain steeped in myth in the Himalayas,  and as such, it would be a mistake to assume that the burgeoning tourist industry could operate freely on every mountain. Similarly, the recent decision to ban tourists from climbing Uluru in Australia may not make economic sense, but consideration of cultural associations clearly is more important.

Some of these cases may seem isolated. But every culture has its own unique relationship with land, which is to some degree (big or small) influenced by myth and legend. Applying the same development strategy in each setting is misguided – and to me it seems this is particularly true for the modern concept of treating the landscape as a commodity to be exploited for profit. Indigenous peoples (in Canada, for example) have treated the land they depend on in a highly sustainable fashion, informed by their cultural memory of fables and myth. We may not be able to return to such a state of living in the modern era, but if we want to build a more sustainable economy and change our current ‘business as usual’ model, it would be fitting to look to those cultures that have achieved a sustainable fashion of living – and particularly fitting to ask ourselves what about their cultural memory encouraged them to live that way.

Robert Emberson is a science writer, currently based in Victoria, Canada. He can be contacted via Twitter (@RobertEmberson) or via his website (www.robertemberson.com).

Heather Britton: Sinkhole Occurrence and Mitigation

Sinkholes are often overlooked geohazards which, although far less destructive in the short-term than earthquakes and landslides, can be catastrophic to life and severely impact the built environment. This post will explore how these features form and the strategies that have been adopted to predict their appearance. It will also consider how urbanisation in karstic areas is accelerating sinkhole formation and what can be done to mitigate these effects.

Sinkholes form most commonly in karstic terrain – topography shaped by the dissolution of soluble rocks such as limestone, gypsum and dolomite. This dissolution creates cavities beneath the ground surface, and the subsidence of the land into these cavities creates sinkholes. Karstic regions are generally associated with three varieties of sinkhole, displayed in the figures below.

  • Figure 1 – Rainfall and surface water percolate through joints in the limestone. Dissolved carbonate rock is carried away from the surface and a small depression gradually forms. On exposed carbonate surfaces, a depression may focus surface drainage, accelerating the dissolution process. Debris carried into the developing sinkhole may plug the outflow, ponding water and creating wetlands. (Source: USGS Water Science School)

    The first are dissolution sinkholes, which form when dissolution is concentrated in a particular area, often along pre-existing joints or fractures within the rock where groundwater flow preferentially occurs. This causes the land to sink in this area and the result is a sinkhole.

  • Cover-subsidence sinkholes are characterised by a thick overburden of granular sediment which gradually falls into an underlying cavity.
  • The final variety, cover-collapse sinkholes, are undoubtedly the most dangerous as they can develop over a period of hours. Cover-collapse sinkholes occur where cohesive material overlies a soluble bedrock. When dissolution occurs in the carbonate/evaporite the overlying cohesive substance will form an arch over the cavity, making it very vulnerable to collapse. In 2013 Jeff Bush disappeared into one such sinkhole as he slept in his home in Seffner, Florida, demonstrating just how catastrophic these geohazards can be.

 

Figure 2 – Cover-subsidence sinkholes, where a thick, overlying, sandy sediment layer fills an underlying cavity, usually produced through carbonate/evaporite dissolution. Source: USGS Water Science School

Figure 3 – Cover-collapse sinkhole formation. Due to the cohesive nature of clay and similar sediment, these sinkholes often do not form gradually and instead tend to appear very suddenly, creating the greatest risk to human life and property. This is usually as a result of an influx of water, causing the layers in the clay to slide over one another. Source: USGS Water Science School

Worryingly, the appearance of sinkholes seems to be on the increase. Urbanisation is accelerating the rate at which sinkholes form, as it is intrinsically linked with processes such as construction and mining. Groundwater pumping associated with construction work changes the natural drainage patterns of the land, leading to dissolution in regions where it has not been seen before. On top of this, increased agriculture to feed the growing population involves the drainage of organic soils, leading to the runoff of organic carbon and the production of highly acidic water sources (pH 3.4-4 recorded in some instances) which inevitably accelerates the dissolution of soluble bedrock. Groundwater pumping in particular was responsible for 80% of identified subsidences in the US where sinkholes are a problem across many states. And the issue is not limited to the US – karstic regions around the world are seeing an increase in the number of human induced sinkholes, for example those which effecting the Madrid-Barcelona High Speed railway. Human activities are undoubtedly impacting sinkhole formation, be it through mining, agriculture or construction.

Aerial view of a large collapse structure, the Tres Pueblos sink, along the Rio Camuy, which exits on the far side of the sinkhole. Solution of underlying rock removed the support and the roof of soil and thin bedrock collapsed into the void. This produces what is known as karst topography. (Courtesy United States Geological Survey)

So what is the best way of allowing development to occur without exacerbating the anthropogenic effect that urbanisation can have on sinkhole formation? One of the simplest and most frequently implemented solutions is to avoid building in regions that may develop sinkholes, or have been shown to be prone to sinkholes in the past. This planned development can be implemented on a small scale, but it is unrealistic to avoid the development of large karstic regions altogether. Carefully considering the drainage networks of new builds and infrastructural projects may help to minimise the effects of development on sinkhole evolution – but sometimes the development pressure is much greater than any impetus to properly consider the state of the land which is being built on.

Currently our best solution to urbanisation in karstic areas is to monitor sinkhole development and attempt to detect them as soon as they appear. Monitoring is possible through geomorphological mapping and the use of GIS and DEM (Digital Elevation Mapping), whilst detection can be achieved with relative ease using geophysical methods (e.g., seismic data and radar). Although not preventative, such techniques do allow sinkholes to be identified early in their development, therefore they can be either avoided or filled before any serious damage is attained.

Even knowing where developing sinkholes lie does not stop construction occurring over them. A short term solution to a developing sinkhole is to fill it, often with concrete, as was done in Zaragoza, Spain. Here the sunken region was waterproofed before being injected with concrete. Whilst it might be thought the initial waterproofing step would end the cycle of dissolution and sinkhole formation, this action was actually seen to increase karstic activity. Filling sinkholes with concrete is not a sustainable solution – it does not prevent sinkholes from continuing to subside (although it may prevent catastrophic collapse) and too much concrete would be required to fill all sinkholes which pose a threat to human property. Other materials are in greater abundance, however, for example rubbish. It is highly unlikely that we will grow short of this ‘resource’ and the planet is currently in need of more landfill sites. The primary risk of this technique is the contamination of groundwater and other water sources – even if rubbish was only used in regions where there was a low risk of water contamination, the danger that groundwater flow would change and begin to poison sources of drinking water would always exist, making this a risky strategy, particularly in regions undergoing heavy urban development or in tectonically active areas. Geologists are working towards solutions – This student paper looks into how sinkholes can be stabilised, removing the danger of collapse – but many sinkholes have unique features which set them apart from the rest, therefore one solution may not be appropriate in all instances.

As the number of sinkholes grows, it is becoming more and more important that we develop better ways of dealing with and preventing this geohazard. Currently our efforts are limited to planning around sinkholes and detecting and monitoring their evolution early, but with urbanisation spreading into karstic regions around the world further work must be done to reduce the risk that this hazard holds for communities. Research is ongoing, and hopefully in the near future will yield not only better detection and mitigation technologies, but more effective and sustainable methods of dealing with sinkholes once they form.