Groundwater level monitoring-importance global groundwater monitoring network

Ramasamy Jayakumar

Asia and Pacific Regional Bureau for Education, UNESCO, Bangkok.

Abstract: The paper illustrates the concept, methodology, essential components and importance of groundwater level monitoring in terms of various aquifers such as multiple aquifer, karst aquifer and other aquifers. The groundwater resources in Mekong countries including Cambodia, Laos PDR, Myanmar, Thailand and Vietnam have also been reviewed.Finally, the author briefly presents Global Groundwater Monitoring Network.

Keywords: Groundwater monitoring; Groundwater resources; Mekong countries; Monitoring network

Introduction

It is estimated that world-wide, almost 900 million people do not have access to an improved drinking water supply, of whom 84% live in rural areas (WHO/UNICEF, 2010). The world as a whole is on track to meet the Millennium Development Goal (MDG) Target to “halve, by 2015 the proportion of the population without sustainable access to safe drinking water”.

We all are groundwater users, farmers use it for irrigation, industries for production and a vast majority of population use it for drinking and domestic purposes. Groundwater, although a renewable resource, is limited in its occurrence in time and space. The mindless pursuit for extracting more and more groundwater by all the users has already started exerting tremendous pressure on this vital resource.

Because groundwater is stored underground, it is better protected then surface water from the threat of pollution from human activities.Processes such as filtration, sorption and natural reduction in the un-saturated zone (i.e. above the water table) work to reduce or eliminate contaminants to enter the groundwater system(ARGOSS, 2001). Groundwater is one of the most important natural resources. In several countries groundwater is the principal source of drinking water. In addition, several countries in the semi-arid region use groundwater for agricultural purposes.

Groundwater has an important role in the environment: It replenishes streams, rivers, and wetlands and helps to support wildlife habitat. It is therefore also a significant, but often unrecognized,component to sustain and maintain of the surface water resources. Around the world, groundwater resources are under increasing pressure caused by the intensification of human activities and other factors such as climate change. Reductions in groundwater storage have implications for the water cycle because groundwater supplies the base-flow in many rivers and it supports evapotranspiration in high water table regions.Reductions in groundwater storage also have major implications for water quality because the salinity of the extracted water frequently increases as the volume of the reservoir decreases. Groundwater resources need to be carefully protected because in many regions, withdrawal rates exceed recharge rates. Once groundwater is modified or contaminated, it can be very costly and difficult to restore.

1 Groundwater monitoring

Groundwater monitoring programme includes both groundwater quantity (e.g. groundwater level and recharge rates) and quality monitoring(analysis of selected physical and chemical variables) networks. Monitoring groundwater is a continuous process. The methodology and techniques are involving in-situ, satellite and airborne observations and laboratory analysis of quality variables.

Groundwater monitoring programmes operate at the international, national, regional and local scales. Local groundwater level monitoring activities often include a great density in terms of time and space, unconfined, semi-confined and confined aquifers for quantity as well for quality.

The use of satellite and airborne observations are valuable to fill in spatial and temporal gaps in in-situ monitoring and, although their reliability is more uncertain when high quality input data are not available.

Satellite observations are now playing an increasingly important role in global groundwater resources assessment and groundwater storage change, but only at lower spatial and temporal resolutions.

The main aims of groundwater monitoring are:

(1) Collecting, processing and analysing the data as a baseline for assessment of the current state, anticipating changes and forecasting trends in groundwater quantity and quality due to natural processes and human impacts in time and space;

(2) Providing information for improvements in the planning, policy and management of groundwater resources.

All these information types, used synergistically, can yield a consistent picture of the current state of global groundwater resources, so that in the future it will be possible to provide more accurate prediction of variations in groundwater availability.

2 Groundwater level

Groundwater level is a term that is used in a relatively loose way, normally referring to the level, either below ground level or reference to mean sea level. This is also referred to as the water table and represents the top of the saturated zone.Above the water table lies the unsaturated zone.

2.1 Why monitor groundwater levels

Groundwater systems are dynamic and adjust continually to short-term and long-term changes in climate, groundwater withdrawal, and land use.Groundwater level measurements from observation wells are the principal source of information about the hydrologic stresses acting on aquifers and how these stresses affect groundwater recharge, storage,and discharge. Groundwater levels reflect the amount of water in storage in the monitored aquifer. When recharge exceeds natural discharge plus abstraction, groundwater levels rise. When recharge is less than natural discharge plus abstraction, groundwater levels will fall.

Long term, systematic measurements of water levels provide essential data needed to evaluate changes in the resource over time, to develop groundwater models and forecast trends, and to design, implement, and monitor the effectiveness of groundwater management and protection programs.

Comparisons of measured groundwater levels with long-term averages provide an indication of the state of groundwater resources within an aquifer. Observations over several years allow the prediction of aquifer response to current climatic and hydrological conditions. The data from the archive are used to prepare archive products such as the monthly hydrological summaries, annual summaries and the statistics volume.

The data are used for quantitative analyses, for instance of annual recharge, and provide a valuable source of data for the calibration of groundwater models.

Benefits of monitoring groundwater levels:

(1) Determine annual and long-term changes of groundwater in storage

(2) Estimate recharges rates

(3) Determine direction and gradient of groundwater flow

(4) Understand how aquifer systems work

(5) Gain insight for well construction and where to set pump bowls for efficient extraction.

2.2 How are groundwater levels measured

Groundwater levels are measured in several ways, manually using a dipper or automatically by a pressure transducer. Automatic readings may be stored in a data logger that is visited periodically and downloaded by field staff, or sent automatically over the phone network to a database in a data centre (telemetry).

However, there is always some components need to be addressed as indicated below:

Multiple aquifers: Where multiple aquifers are present there may be significant differences in water level between aquifers, especially if there are perched water tables or confined aquifers making it unclear which aquifers are measured.

Karstic aquifers: In karstic aquifers and other aquifers where fissure flow dominate there may be no defined water table in a regional sense, but rather each fracture system may respond independently, leading to significant variations in level over short horizontal or vertical distances.

Clays: In clays a water table may be present,but not be a useful concept, if the low permeability of the clay prevents the draining of surface water.

Seasonal variations: Seasonal variations in level range from a few centimetres in some confined aquifers to several tens of metres. Interannual variations show similar fluctuations in response to climatic variations.

Pumping: Levels may be artificially depressed by pumping. Where regional depressions occur it is the current depressed level that is normally of interest, although reversion to the natural“unpumped” level is likely if pumping ceasesfrequently historical data has been gathered during periods when pumping was intense, and less data may be available after pumping stops. Where unrecognised localised depression of the water table occurs through pumping they may distort interpolations of regional levels that include measurements made in nearby boreholes. More rarely levels may be higher in observation boreholes due to localised recharge leading to groundwater mounding. Measurements made during or immediately after the drilling of a borehole may be affected by the injection or extraction of water as part of the drilling process.

3 Essential components of groundwater level monitoring

3.1 Selection observation wells

All groundwater level monitoring programs depend on the operation of a network of observation wells for the collection of water-level data in one or more specified aquifers. Decisions made about the number and locations of observation wells are crucial to any water-level data collection program. Ideally, the wells chosen for an observation well network will provide data representative of various topographic, geologic,climatic and land-use environments.

Groundwater level monitoring programs for complex, multilayer aquifer systems may require measurements in wells completed at multiple depths indifferent geologic units. Large, regional aquifers that extend beyond country/province boundaries require a network of observation wells distributed among one or more country/province.

When the groundwater level monitoring is part of the ambient groundwater resources, or the effects of natural, climatic-induced hydrologic stresses, the observation network will require wells that are unaffected by pumping, irrigation. For further reading on many other technical considerations pertinent to the design of a groundwater level observation network are discussed in more detail in technical papers by Peters (1972), Winter (1972), and Heath (1976).

3.2 Frequency of groundwater level measurement

The frequency of groundwater level measurements is the most important components of a monitoring program. Although often influenced by economic considerations, the frequency of measurements should be determined to the extent possible to fully characterize the hydrologic behaviour of the aquifer.

Typically, collection of groundwater level data over one or more decades is required to compile a hydrologic record that encompasses the potential range of groundwater level fluctuations in an observation well and to track trends with time. The availability of long-term water-level records greatly enhances the ability to forecast future water levels. Therefore, observation wells should be selected with an emphasis on wells for which measurements can be made for an indefinite time.

3.3 Quality assurance

To maintain the accuracy and precision of groundwater level measurements, ensure that observation wells reflect conditions in the aquifer being monitored, and provide data that can be relied upon for many intended uses. The locations and the altitudes of all observation wells should be accurately surveyed to establish horizontal and vertical datum for long-term data collection.Recent advances in Global Positioning System(GPS) technology, have simplified the process of obtaining a fast, accurate survey of well location coordinates and datum.

To help maintain quality of the data, a permanent file that contains a physical description of well construction, location coordinates, the datum used for groundwater level measurements,and results of hydraulic tests should be established for each observation well.

3.4 Data reporting

The accessibility of groundwater level data is greatly enhanced by the use of electronic databases,which is compatibility with Geographic Information System (GIS) technology to visually depict the locations of observation wells relative to pertinent geographic, geologic, or hydrologic features.

Hydrographs, the graphical plots showing changes in water levels over time are particularly useful form of data reporting. Such hydrographs provide a visual depiction of the range in waterlevel fluctuations, seasonal water-level variations,and the cumulative effects of short-term and long-term hydrologic stresses.

4 Status of groundwater resources in Mekong countries

4.1 Cambodia

Status of groundwater resources in Cambodia:

• Groundwater is available almost everywhere in plain area except Dry-Zone in Central and Northwest region;

• Groundwater study is in progress (7 provinces out of 24 completed);

• Groundwater is major source for drinking water supply in Cambodia; 53% of Cambodian households uses groundwater sources during dry season;

• No data available for Groundwater Exploitation in Cambodia yet. About 270 000 tube-wells with hand pump are functioning for drinking water purpose.

Major issues and challenges threatening groundwater resources:

• Groundwater quality problems with high arsenic and iron (Fe) contents in Mekong and Tonle Sap river basin (along the rivers);

• Saltwater intrusion in coastal aquifers(Southeast Provinces);

• Industrial zones are expanding in Cambodia;potential problems of groundwater contamination from untreated industrial wastes;

• Currently, groundwater is used only for small community water supply; but trends to exploit more groundwater for industrial use and agricultural irrigation;

• Potentials major threat is over exploitation without legal control of groundwater administration. Groundwater management partially included in the Water Resources Law.

Government interventions for groundwater issues:

• Investigation and testing for Arsenic reduction technology development by MRD/NGOs and Institute of Technology of Cambodia;

• Potable Iron Reduction Plants are developed and installed on high-iron content tube-wells(operated with hand pump);

• Continuation of Groundwater Study in Northeast Region (By MRD with assistance of JICA) Groundwater Database under developing (by MRD/ MOWRAM with WB assistance);

• Groundwater Water Quality Mapping by MRD in cooperation with RDI (NGO) and WHO.

Challenges:

• At present groundwater are extracted from shallow aquifers; there are potentials for exploration of deep aquifers (deeper than 200 m). These deep aquifer explorations required updated technology applications;

• Groundwater, river basins and shallow aquifer areas are always replenished by rainwater and river-flood water. Climate change impact can affect to groundwater recharge in these areas;

• Salt water intrusion in Coastal region is big challenges; need technology development to control of mitigate impacts.

Policy supports to increase groundwater resource sustainability:

• Law enforcement on Groundwater Management and Environmental Laws to protect Groundwater contaminations;

• Groundwater Studies (investigation, groundwater mapping,) are essential for Groundwater Resource Management;

• Groundwater Database and Functional Monitoring System establishment (on quality and quantity) related with inter-ministerial cooperation;

• Mekong River is one important source for recharging of shallow groundwater and subsurface in Cambodia. Mekong River Management is a regional issue (Sok Sophally,2011).

4.2 Laos PDR

Status of groundwater resources in Laos PDR: Groundwater is emerging as a large and generally untapped resource. However, there is very little monitoring of groundwater quality in Lao PDR, even though it is the main source of rural water supply. There are three different aquifer systems:

• The Annamian aquifers occur randomly. These are local systems that discharge locally to the river or its tributaries. As local flow systems, they are not part of the regional flow system and will not carry pollution into the regional groundwater system. The potential water supply from groundwater in the northern part of the country is considerable in view of the high amount of recharge available. Water quality should be reasonably good and for the most part potable but will be iron rich. Yields up to 5 liters/sec can generally be anticipated;

• The Indosinian group of aquifers, which have regional flow, includes rock of the Indonisian Moyennes and Superieures and is relatively young. They are mostly freshwater sediments,although there are horizons of brackish water,and one major zone of saline water. Yields of 12-24 liters/sec can be developed;

• The alluvial aquifers associated with the sedimentary deposits of the Mekong River are not rated highly as aquifers (Water Environment Partnership in Asia, 2015).

Major issues and challenges threatening Groundwater Resources:

• Groundwater resources extent and quality largely unknown, because lack of systematic monitoring, borehole logging and yield test;

• No systematic or national approach to defining the groundwater resource means using groundwater for water supply is often a high risk option for water supply;

• Climate change-abnormally fluctuating shallow groundwater levels can have a significant impact on iron and manganese content of shallow groundwater, need further studies;

• Lack of a water quality data base means that for example “arsenic hotspots” on the plains of Southern Lao are now just being recognized as an issue. Problem is that in many cases there is no alternative to the existing, inexpensive shallow dug wells.

Policy g barriers towards groundwater resource sustainability:

• Policies need to be supported with timely Decrees in order to implement the Regulations and Decisions;

• Need all kinds of resources to support the policies and inter-ministerial cooperation is required (Phouvong Chanthavong, 2011).

4.3 Myanmar

Status of groundwater resources in Myanmar:

• On the basis of stratigraphy, there are 11 different types of aquifer in Myanmar;

• Depending on their lithology and depositional environments, groundwater from those aquifers has disparities in quality and quantity;

• Out of those, groundwater quality of Alluvial and Irrawaddian aquifers is more potable for both irrigation and domestic water use;

• In the water scarce regions, groundwater from Peguan, Eocene and Plateau limestone aquifers, though not totally suitable for drinking purpose from hygienic point of view,are extracted for domestic purpose;

• Water use in Myanmar has been on the increase particularly in the agricultural and industrial sectors;

• It is found out that as much as 89 percent of water use is tapped for irrigation purpose,about 8 percent is for domestic consumption and 3 % is for industry.

Major issues and challenges threatening groundwater resources:

• Groundwater is the principal source of domestic water supply in Myanmar;

• Between 1952 and 1976, RWSD (predecessor of WRUD) constructed 6261 tube wells serving some 4.5 million rural populace(These works were funded by the government);

• Negotiations initiated in 1976 with resulted in the formulation of a tube well program in the dry zone of central Myanmar which comprised the construction of 3 100 tube wells for the three regions of Sagaing, Magway and Mandalay (implemented in 1977-1978 with the combined resources of the Government and external agencies, namely WHO. UNICEF and ADAB);

• So far, WRUD has completed a total of 38320 tube wells in different types and sizes for drinking water supply throughout the country(U Aung Khaing Moe, 2013).

Experts warn of groundwater depletion dangers:

While some areas of Myanmar suffer from dwindling water supplies during summer, it is not unusual at this time of year to see water dripping from overflow pipes set outside high-rise buildings in Yangon (Aye Sapay Phyu, 2014).

4.4 Thailand

Status of groundwater resources in Thailand:

• The stress on water in the main development regions is especially heavy, and groundwater has become an important resource for industrial use and urban water-supply.Moreover, as a consequence of recent droughts,it has become more widely exploited for irrigated agriculture to insure dry-season cropping;

• Thailand needed a soundly-based and effectively-implemented management system to ensure sustainable and efficient use of its valuable groundwater resources. In general terms it can be said that all of the major alluvial aquifers possess very large reserves of freshwater in storage, but their rates of active replenishment (while very significant) are still subject to a large degree of uncertainty.

Major issues and challenges threatening groundwater resources:

• Careful monitoring of the aquifer response to existing or new pumping, and to alreadyexistent pollution plumes, is the cost-effective way of confirming conceptual models, and calibrating numerical models, used as the basis for groundwater management;

• A particularly important need is to assess shallow aquifer recharge mechanisms and rates, together with evaluation of shallow-deep aquifer interactions, in typical alluvial aquifer situations. This is related to the field assessment of hydrogeological sustainability and socioeconomic benefits of existing informal conjunctive use of groundwater for supplementary agricultural irrigation;

• There was also a need to rationalise data basing, including establishment of a computerised linkage system (with joint numbering and agreed location) between well-based entries in the scientific hydrogeologic database and the abstraction regulation database, and also widening the data-capture up-grading and completion of the computerised regulation database (IGRAC,2015).

4.5 Vietnam

Status of groundwater resources in Viet Nam:

The Vietnamese territory can be divided into 6 hydrogeological regions (HGR)

• West BắcBộ HGR located in folded mountain structure in West BắcBộ. This is a complicated hydrogeological region;

• East BắcBộ HGR belonging to formation of mountainous area in East BắcBộ;

• BắcBộ Delta HGR including the whole delta plain in North Việt Nam, which extends from ViệtTrì City to the East Sea. This delta is built up by Red and TháiBình River systems;

• North TrungBộ HGR including coastal plain provinces in the north of Central Việt Nam such as Thanh Hóa, NghệAn, HàTĩnh, Quảng Bình and Thừa Thiên- Huế;

• South TrungBộ HGR including coastal plain provinces in the south of Central Việt Nam such as TuyHoà, BìnhThuận and Nha Trang-KhánhHoà;

• Nam Bộ Delta HGR including the whole delta plain of Mekong and ĐồngNai River systems.

Groundwater on the Vietnamese territory exists in following formations:

• Groundwater in loose sediments is distributed mainly in two large delta;

• Groundwater in basalts is distributed mainly in the TâyNguyên plateau belonging to the Kon Tum, Gia Lai, ĐắcLắk, LâmĐồng Provinces and some provinces of South TrungBộ and East Nam Bộ;

• Groundwater in carbonate (karst aquifer)occupies an area of 50 000 km2;

• Groundwater in crushed formations (terrigenous sediments, effusive, intrusive and metamorphic rocks) usually has good quality and satisfies the water use demands. However,because of small reserve, its exploitation is scattered with each well of only some cubic meters per day of output.

Major issues and challenges threatening groundwater resources:

Issue of quality management is an urgent problem not only at present but also in the future.To manage and control the quality of water sources,we need to perform the following works:

• Obeying strictly protective requirements for water sources during the time of exploitation and use;

• Establishing protective areas and belts to protect aquifers;

• Managing successfully and controlling strictly waste and pollutant sources that lead to the degradation of water quality;

• Building monitoring systems for the fluctuation of groundwater;

• Assessing the environmental impact to factors causing pollution and exhaustion of water sources, such as annulation of natural recharge sources (forests, rivers, streams…), exploitation of water with large output and in long time, mineral exploitation causing serious influence to groundwater quality and reserves.

Solutions for managing and protecting groundwater resource:

To well perform the task of management and protection of precious groundwater resource, we need to realize the following works:

• Seriously designing a law for water resource protection;

• Strictly realizing guides, decretes and underlaw documents. Managing successfully the works of drilling for groundwater exploitation.Listing water exploitation works to establish database for different works;

• Propagandizing broadly to people the ways to exploit and use water effectively and economically. By late years of this decade, all people should have good sense in the protection of water resource;

• Building protecting zones for water sources,especially in present exploiting areas of HàNội,HồChi Minh Cities and other urban areas…

• Modernizing water management work. It is necessary to have immediately courses on water management for individual, community and organizations related to the exploitation and protection of groundwater;

• Processing pollutant and toxic waste sources which there influence on water sources;

• Planning and building water exploiting centres to manage and supply with water more effectively to minimize catastrophes during exploiting process (BÙI HỌC PHẠM KHÁNH HUY and HOÀNG THỊ MINH THẢO, 2005).

5 Global Groundwater Monitoring Network (GGMN)

Groundwater is monitored in many parts of the world by measuring groundwater levels, groundwater abstraction rates, spring discharge and groundwater quality. Groundwater level point measurements are often interpolated and combined with other data (e.g. remote sensing and modelling)to assess the state of groundwater resources.

There is however, a lack of information on groundwater monitoring at the regional and global scales, which hampers assessment and informed water management. Recognizing the need for a systematic collection of groundwater data, IGRAC took initiative to establish the Global Groundwater Monitoring Network (GGMN). The GGMN is a programme in which groundwater data from a global network of groundwater professionals is gathered, processed and made accessible to a range of stakeholders. The GGMN Programme combines groundwater experts and technological services into an online portal that facilitates the assessment of changes to groundwater resources globally. The GGMN Programme consists of two components:the GGMN Portal and the GGMN People Network.

5.1 The GGMN Portal

The GGMN Portal enables users to produce online maps showing groundwater changes over time on a regional scale. A web-based software application assists in the analysis of monitoring data and gives insights into changes occurring in groundwater levels worldwide. The simplicity of the application and clear information ownership (it remains with the data supplier) ensure the essential support and commitment of the global groundwater community for the GGMN Programme.

5.2 Country workspace

Groundwater specialists, who are members of the GGMN People Network, can access the country-dedicated workspace of the portal. This workspace allows users to upload, interpolate,aggregate and analyse the groundwater data from their country using the following steps:

(1) Representative groundwater point measurements are uploaded. Alternatively, the measurements can be transferred from a national system via web services;

(2) Point data are spatially aggregated per grid cell using customised grid overlays. Automatic interpolation can be used as a first step to interpolate available point data;

(3) Final adjustments are made manually, using available proxy information and personal expertise;

(4) Time series analysis can be performed for each point measurement location. This functionality is currently being extended to also allow for the optimisation of monitoring frequency.

5.3 Public view

The GGMN portal has a public view mode that is meant for the general public, including researchers, consultants, teachers, policy makers and NGOs. Changes in groundwater level point measurements can be calculated and visualised over time on a regional and a global scale. It also allows simultaneous display of the country-based spatial aggregations to create a regional or a global picture of the state and changes of groundwater levels. With permission from countries and data owners, the data sets can be used for calibration and verification of numerical models and remote sensing data.

5.4 Future database connections

Many countries already have online databases but currently only few provide open-access to groundwater data. In collaboration with the countries championing international data sharing,IGRAC is establishing automated data flows between these countries’ national databases and the GGMN. Other countries are encouraged to follow these examples. In the meantime, they can join the People Network and upload measurements into the GGMN portal themselves via the country workspace.