Much of the world’s population relies on groundwater for its water supply. But with growing demand and increasingly frequent shortages, this resource is becoming more precious and should therefore be managed with great care. More effective monitoring is required for issues such as groundwater recharge, and the effects of water use, drought, pollution and climate change.

BACKGROUND

In December 2020, the world population was estimated to be 7.8 Billion, and is expected to reach 8.6 billion in 2030, 9.8 billion in 2050 and 11.2 billion by 2100. This places growing pressure on all-natural resources including water. According to the United Nations World Water Development Report 2018, the global demand for water has been increasing at a rate of approximately 1 % per year in recent decades. This is due to issues such as population growth, economic development and changing consumption patterns, and demand will continue to grow significantly in the foreseeable future. Industrial and domestic demand for water will increase much faster than agricultural demand, although agriculture will remain the largest user overall with around 70%. Most of the growth in demand for water will occur in countries with developing or emerging economies. At the same time, climate change is generally causing wetter regions to become wetter, and drier regions to become even drier, resulting in increased risk of flooding and drought. Other global changes such as urbanization, de-forestation and the intensification of agriculture, add to these challenges and combine to place enormous pressure on water resources.

THE ROLE OF GROUNDWATER

Freshwater accounts for just 2.5% of the Earth’s water, with most of it frozen in glaciers and the icecaps. The remaining freshwater is mainly groundwater, with only a small fraction present as rivers, lakes, reservoirs, precipitation, clouds etc. Groundwater is mostly derived from rivers, streams and precipitation which soaks into the ground where it is stored underground in the pore spaces between soil particles and in rock fractures. These underground water resources are known as aquifers and the upper surface of the saturated zone is called the water table.

Groundwater measurement site.

Performing an important role in the Water Cycle, groundwater drains from springs and seepages into streams, rivers and oceans. This contribution to river flow is known as base flow and is responsible for maintaining the flow of rivers during extended periods of dry weather, when surface runoff virtually ceases.

In the European Union 75% of the population depend on groundwater for their water supply. Groundwater is also a vital resource in the USA; supplying around 37% of the water that county and city water departments supply to households and businesses.

It also provides drinking water for more than 90% of the rural population. In the USA about 42% of the water used for irrigation comes from groundwater.

GROUNDWATER SUSTAINABILITY

Groundwater is usually of high quality and is commonly withdrawn as a supply for drinking water and to support agriculture in dry areas. Groundwater can be considered a renewable resource i it is not withdrawn faster than it can be replenished naturally. However, in many dry regions’ groundwater is not renewed or only very slowly, which highlights the importance of monitoring. Groundwater abstraction rates need to be sustainable; and the only way to achieve that without relying on luck, is to monitor continuously. When groundwater is treated as an unlimited resource and the effects of its utilization are not monitored, there is serious risk that it will become exploited with deleterious effects on quality and quantity.

GROUNDWATER STATUS IN THE USA

The United States Geological Survey (USGS) is one of several federal agencies that monitor water resources, water use and availability.

Water use in the United States in 2015 was estimated to be about 322 Billion gallons per day which was 9% less than in 2010. In 2015 fresh surface-water withdrawals were 14% less than in 2010; however, fresh groundwater withdrawals were about 8% greater than in 2010.

Although groundwater provides 25% of the freshwater used in the USA, it provides 43% of the freshwater used for irrigation. Groundwater resources in the United States are not evenly distributed. In some areas, particularly in the more arid West, groundwater use is greater than groundwater recharge.

GROUNDWATER STATUS IN EUROPE

According to the European Environment Agency (EEA) despite an estimated decrease of total water abstraction of 19% since 1990 in Europe, the target for water abstraction remaining below 20% of available renewable water resources was not achieved in 36 river basins (around 19% of Europe) in the summer of 2015. Around 30% of the total European population was exposed to water scarcity conditions in summer 2015 compared to 20% in 2014; mainly in densely populated cities, agriculture-dominated areas of southern Europe and small Mediterranean islands. In 2009, the EEA produced a report entitled: ‘Water resources across Europe – confronting water scarcity and drought’ which highlighted the imbalance between water demand and availability, describing the situation as critical in many areas of Europe. The report said that reduced river flows, lowered lake and groundwater levels, and the drying up of wetlands are widely reported, alongside detrimental impacts on freshwater ecosystems, including fish and bird life. In addition, climate change will almost certainly exacerbate these adverse impacts in the future, with more frequent and severe droughts expected.

Groundwater measurement site.

Under the EU Water Framework Directive (WFD), all river basins in Europe should be managed using a River Basin Management Plan. Member States shall ensure that a plan is produced for each river basin district lying entirely within their territory, and it must include a summary of pressures and impacts of human activity on groundwater status, a presentation in map form of monitoring results, a summary of the economic analysis of water use, a summary of protection programmes, control or remediation measures etc.

AFFECTS ON GROUNDWATER

One factor affecting groundwater resources is drought. Droughts reduce groundwater recharge and thereby lower sustainable abstraction rates. In addition, groundwater is often exploited as an alternative or supplemental source of water during droughts. Lower groundwater levels due to drought or increased pumping can result in decreased water levels and flows in surface water resources such as rivers and streams. In addition to the effects on water quantity, there may also be effects on water quality and ecology. Reduced heads in aquifers can also cause land subsidence.

Droughts are the most detrimental of all the natural disasters (Bruce 1994, Obasi 1994, Cook et al. 2007, Mishra and Singh 2010). Globally, about one-fifth of the damage caused by natural hazards can be attributed to droughts (Wilhite 2000), and the cost of droughts is estimated to be around USO 80 billion per year (Carolwicz 1996).

In a study published in the journal Nature (Schwalm 2017), researchers found that more of the Earth’s land surface is now being affected by drought, and ecosystems are taking longer to recover from dry periods. Recovery was found to be worse in the tropics and at high latitudes; two areas that are already vulnerable to global change.

Traditionally, assessments of drought and recovery have focused on hydrology; the effects of precipitation on water in rivers, lakes, and soils. In the study, researchers addressed the health and resilience of plants because full reservoirs and rivers do not necessarily mean that vegetation has recovered. The analysis showed that plants in many regions are taking longer to recover from drought, often because weather is more extreme than in the past. lf the time between droughts grows shorter, and recovery times become longer, some ecosystems could be permanently affected, resulting in less carbon sequestration, and thereby accelerating the warming that leads to more drought.

Another factor affecting groundwater resources is the ongoing climate change. More extreme precipitation events may lead to more groundwater recharge, but water from heavy storms tends to runoff directly into rivers and other surface watercourses, so the effect of high precipitation on groundwater is less significant. In case drier seasons become drier and warmer, the recharge period may be shorter so overall there would be less recharge.

During hot summers the main impact on groundwater is an increase in demand, especially if the flow in rivers is reduced. With an increasingly stressed environment, it will be necessary to balance water demand for agriculture, industry and public supply.

Furthermore, climate change is the likely rising of sea levels. This may lead to the loss of groundwater resources in very low-lying coastal areas, because sea water can flow into aquifers and mix with freshwater.

There is substantial evidence that human-induced climate change has led to an increase in the frequency, intensity and/or amount of heavy precipitation events at the global scale (medium confidence), as well as an increased risk of drought in the Mediterranean region. In the report, Working Group II of AR5 (IPCC Sth Assessment Report) concluded that the detection of changes in groundwater systems, and attribution of those changes to climatic changes, are rare, owing to a lack of appropriate observation wells and an overall small number of studies (Jimenez Cisneros et al., 2014). Since ARS, the number of studies based on long-term observed data continues to be limited.

The groundwater-fed lakes in north eastern central Europe have been affected by climate and land-use changes, and they showed a predominantly negative lake-level trend in 1999- 2008 (Kaiser et al., 2014). WGII ARS concluded that climate change is projected to reduce groundwater resources significantly in most dry subtropical regions (high confidence) (Jimenez Cisneros et al., 2014).

Climate change adds further pressure on water resources and exaggerates human water demands by increasing temperatures over agricultural lands (Wada et al., 2017). Portmann (2013) indicated that climate change by 2° c would result in 2% of the global land area suffering from an extreme decrease in renewable groundwater resources. Researchers at Cardiff University have warned of an environmental time-bomb in relation to the effects of climate change on groundwater resources. Published in the journal Nature Climate Change (Cuthbert 2019), the research team have shown that in more than half of the world’s groundwater systems, it could take over 100 years for groundwater systems to completely respond to current environmental change. More frequent extreme weather events will result in greater frequency of flooding, so there is a growing demand for improved understanding of the factors affecting flooding, not least because budgets for mitigation measures are dictated by the potential costs of flooding. Raised groundwater levels can play a significant role in floods, but this is often overlooked, with most floods being blamed on overflowing surface water channels. In Saxony, Germany during 2002, 16% of flood damage was found to have been caused by groundwater flooding (Huber et al., 2003).

Rising groundwater levels are a concern in areas where groundwater levels are already high. In the Netherlands for example, rising groundwater can cause wet crawl spaces, mould in buildings and health problems for residents. Increased groundwater levels under roadways can also contribute to foundation instability. This also renders basements vulnerable to damage from cracks and leaks, and exposes plants to root-zone oxygen deficiency, which damages crop yields and increases the risk of falling trees.

GROUNDWATER OVER-USAGE A GLOBAL PROBLEM

Groundwater is used for agricultural irrigation, in the clean water supply system and by industry – as a water supply in the food and beverage industry, as a solvent, for cleaning, and for cooling in a wide range of processes. lt follows therefore, that water over-usage will follow in countries with increasing populations, especially in areas with a growing or developing agricultural sector.

The main factors affecting crop growth are nutrients, sunlight and water availability, so as drilling and pumping technology became more easily available, farmers have been able to boost yields by exploiting groundwater resources. However, in warm dry areas a high proportion of irrigation water is lost to evaporation and evapotranspiration from plants. lf groundwater abstraction exceeds the natural groundwater recharge for extensive areas and for long periods, overexploitation or persistent groundwater depletion occurs. The resulting lowering of groundwater levels can have devastating effects on natural streamflow, groundwater fed wetlands and related ecosystems. In addition, a drop of groundwater levels in coastal areas, can lead to land subsidence and saltwater intrusion.

Research involving the global modelling of withdrawal, allocation and consumptive use of surface water and groundwater resources, (Wada et al 2010) suggests that during 1990-2010 people have increasingly relied on groundwater, because surface water has been extensively exploited during earlier periods. Readily accessible groundwater is an obvious choice to fill the gap between the increasing demand and limited surface water availability, but this increasing dependence on groundwater is likely to worsen the groundwater depletion that has already been reported in regions such as northern Iran, north western India, north eastern Pakistan, north eastern China, Mexico, and the western and central USA.

INTERNATIONAL POLITICS

In the past, groundwater has suffered from a lack of PR, particularly in comparison with its celebrity sibling surface water. Journalists and politicians rush to the opening of a new reservoir, but few attend events relating to underground water. However, as the effects of climate change become better understood, governments and international organisations are starting to place a greater emphasis (and more money) in the management of water resources.

According to the World Bank, there are 276 transboundary basins, shared by 148 countries, which account for 60% of the global freshwater flow. Similarly, 300 aquifers systems are transboundary in nature, and 2 billion people worldwide are dependent on groundwater. Cooperation is therefore needed to achieve optimal water resources management. To achieve this, reliable monitoring data will be necessary to build trust and inform decisions on the development of solutions for all stakeholders. To deal with these complex and interlinked water challenges, countries will need to improve the way they monitor and manage their water resources.

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MONITORING GROUNDWATER

In many parts of the world, OTT HydroMet has witnessed a significant growth in the sale of groundwater monitoring instruments and systems, which is an encouraging sign that greater attention and budget is being applied to this important resource. In total, OTT HydroMet has now sold more than 43,000 units globally for continuous groundwater measurement systems. Approximately 30,000 of these have been for long-term monitoring.

The United Nations Sustainable Development Goal 6 (SDG 6) seeks to support countries in monitoring water and sanitation related issues within the framework of the 2030 Agenda for Sustainable Development. The long-term goal is to establish and manage a coherent monitoring framework for water and sanitation to inform progress towards the 2030 Agenda, and to contribute to country progress through well shared by 148 countries, which account for 60% of the global 2030 Agenda, and to contribute to country progress through well progress through well informed decision making in the water sector.

Measuring Site OTT ecoLog 1000.

Within SOG 6 the key targets relating to groundwater are: 6.4 By 2030, substantially increase water-use efficiency across all sectors and ensure sustainable withdrawals and supply of freshwater to address water scarcity and substantially reduce the number of people suffering from water scarcity. 6.5 By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate. 6.6 By 2020, protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes.

According to the UN, the purpose of monitoring is to help policy and decision makers at all levels of government to identify challenges and opportunities, set priorities for more effective and efficient implementation and communicate progress, or lack thereof (and therefore associated requirements), to ensure accountability and generate political, public and private sector support for further investments.

Over the past decade integrated groundwater monitoring networks, such as the US National Ground-Water Monitoring Network have been piloted, validated and expanded. Such networks aggregate selected groundwater data collected from federal, state and local agencies in a data portal to make datasets spanning state, county and aquifer boundaries more readily accessible.

Groundwater data accessibility is a topic on increasing interest. Even through groundwater moves more slowly than surface water, issues including drought, population growth, migration and climate change are driving the need for real-time data collection and alarm systems. Such systems, including the OTT ecoLog groundwater level loggers, provide all in-one, compact systems for measuring, collecting and transmitting data from the well to the office. The management and utilization of data sets with increasing spatial and temporal frequency requires powerful but easily accessible data management systems such as Hydromet Cloud, a web-enabled data visualization and management tool that provides water resource managers with an opportunity to monitor an entire network of wells continuously from anywhere at any time, using any web-enabled device. This network monitoring capability delivers a wide variety of advantages; enabling users to monitor trends across an entire catchment, correlating groundwater recharge with other key measures such as precipitation, river level and flow data. lt is even possible to include soil moisture sensors into a monitoring network so that groundwater status can be assessed from a meteorological, hydrological and agricultural perspective.

The trend being observed by OTT HydroMet has been for significant growth in the market for remote monitors with real-time data communications capability.

MONITORING GROUNDWATER IN THE USA

The states have primary responsibility for groundwater management; however, several federal agencies monitor, forecast, and assess groundwater conditions. The USGS has monitored and reported groundwater conditions across the country for decades. lt has also developed groundwater models for characterizing aquifers; and provided long- and short-term forecasts of changing groundwater conditions as part of local and regional groundwater studies. This information is used to inform decision making at a federal, state, and local level, and is often conducted in collaboration with federal, state, and local partners. For example, the data from the National Ground-Water Monitoring Network, a USGS distributed water database, is freely available to stakeholders. The database is fed by a locally managed network of stations that monitor surface water flow, groundwater levels, and water quality, and includes both long and short-term records from more than 850,000 groundwater measurement sites.

California’s Sustainable Groundwater Management Act of 2014 (SGMA), incorporates climate change into water planning because groundwater serves as a buffer during dry periods, and can store huge volumes of water during floods. The SGMA provides a state-wide framework that incentivizes the flexible management of groundwater basins, in part because it recognizes the impacts that climate change will have on water management and requires water managers to incorporate these impacts. For example, Groundwater Sustainability Agencies have to incorporate quantitative climate change assessments into projected water budgets. Groundwater data and water-use information are both critical components of water budgets, which are essential to surface water and groundwater availability studies.

MONITORING GROUNDWATER IN EUROPE

European Member States are required to establish groundwater monitoring networks based on the results of a classification analysis to provide a comprehensive overview of groundwater chemical and quantitative status. The WFD daughter Groundwater Directive (GWD 2006/118/EC) establishes a reg1me which sets groundwater quality standards and introduces measures to prevent or limit inputs of pollutants. The directive establishes quality criteria that take account of local characteristics and allow for further improvements based on monitoring data and new scientific knowledge. The directive thus represents a proportionate and scientifically sound response to the requirements of the WFD as it relates to assessments on the chemical status of groundwater and the identification and reversal of significant and sustained upward trends in pollutant concentrations.

The Common Implementation Strategy (CIS} for the WFD provides a document entitled: Guidance on Groundwater Monitoring, which details the requirements for Quantity Monitoring, Surveillance Monitoring, Operational Monitoring, Drinking Water Protected Area (DWPA) Monitoring, and Prevent and Limit Monitoring. The Guide aims to establish cost-effective, risk-based and targeted groundwater monitoring across Europe, but warns that inadequate investment in monitoring, including network infrastructure and data quality and management, will result in a significant risk of failure to meet the WFD’s environmental objectives.

GROUNDWATER MONITORING CHALLENGES

Given the challenges that groundwater faces, globally this vital resource needs more effective monitoring, both spatially and temporally. More monitoring sites will be necessary if a clearer picture of groundwater resources is to be developed. Without adequate spatial distribution of continuously monitored wells, water resource managers will have to rely too heavily on models with unacceptably high levels of uncertainty. In addition, more frequent monitoring will be necessary, partly to better inform the models, but also to raise earlier, more timely warnings when potentially detrimental conditions occur. Groundwater is a critical component of the Water Cycle, so the whole cycle needs to be monitored effectively. This means that continuous precipitation and river level monitors, for example, will need to be complemented by more than just an annual tape down measurements. Groundwater levels certainly change more slowly than surface water, but continuous datasets are necessary so that the causes and effects of level changes can be identified in the context of whole catchment or river basin monitoring.

The technology for continuous groundwater level monitoring is well established and relatively low cost, with most sensors employing a vented, temperature compensated pressure transducer. Such sensors need to be robust and low power to facilitate long-term deployment. For example, OTT’s groundwater level loggers typically employ a robust ceramic pressure cell in stainless steel tubing with Kevlar-reinforced cable. Same of the probes also include conductivity sensors which offer additional advantages such as the detection of saltwater intrusion. They can also be used to monitor at different depths so that the levels of freshwater and saltwater can be measured. This is particularly important for small oceanic islands, such as those in the Caribbean or Hawaii, which have very delicate freshwater or saltwater balances because the volume of fresh groundwater is so low. Changes in groundwater conductivity can also provide an indication of changes in water quality. This is because conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulphate, and phosphate anions, or sodium, magnesium, calcium, iron, and aluminium cations. This is a useful measure 1n areas threatened by nitrate pollution – from agricultural fertilizers for example.

LOOKING FORWARD

There is an incontrovertible need for more data so that water resources can be better managed and protected in the future, and there are three key issues making this possible. First, ‘Big Data’ is impacting almost every area of life, and water resources are no exception. The ability to manage enormous datasets has advanced considerably in recent years and looks set to continue as more people take advantage of the benefits that this provides. Second, communications technology has advanced considerably, offering water managers the opportunity to view water resources in real-time using any web-enabled device. This capability also enables the implementation of alarm systems that can issue warnings when potentially dangerous conditions arise.

OTT ecoLog 1000 application.

Third, sensor technology is advancing rapidly. This has meant that monitoring systems can be left to operate reliably, unattended in remote locations for extended periods – often for months, if not years. The latest sensors combine with communications technology to continuously relay their ‘health status’ as well as current readings. This means that proactive service can be undertaken, when necessary, to lower costs and minimise downtime. As a result of the changes mentioned above, we at OTT HydroMet estimate that the number of site visits to collect samples will be dramatically reduced, costs will be lowered and the value of data will be enhanced as we progress toward integrated water resource management. By making groundwater visible, societies are more likely to find ways to reduce consumption. For example, new irrigation methods are more efficient, grey water reduces demand on freshwater, and citizens can reduce consumption with more water efficient household devices. In addition, the water footprint of products is becoming better known, which encourages supply chains to find ways to lower water consumption and helps citizens to include water footprint in their buying decisions.

SUMMARY

A growing global population, over-use of water resources, extreme weather, climate change, pollution and insufficient groundwater recharge, all combine to place enormous pressure on groundwater. In the past, the effects of these issues have been largely unseen, but in the 21 st Century technology is making the unseen visible.

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lt has become clear that good data is essential in the search for good solutions, and for figuring out which solutions work. Water resources do not respect borders, so international cooperation will be necessary. To achieve this all stakeholders will need to be able to trust the data, so it must be accurate, comprehensive and reliable. Thankfully, the technology to do so is now available so groundwater is no longer a hidden resource and is starting to enjoy the celebrity status that it deserves.

By Graham Meller, Buttonwood Marketing Limited, Buttonwood House, Main Rd, Shutlanger, Towcester, Northants NN12 7RU, England