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An introduction to this special section

Hydrogeophysics

Kansas Geological Survey

Water is obviously essential for human survival. Energy, in one form or another, is critical to all life and necessary to the current and future world economy. There are renewable and nonrenewable forms of both water and energy. Energy is or has been the focus of much debate, research, exploration, regulation, and incentives. Similarly, potable water is globally explored for, commonly regulated and monitored, treated/refined, and throughout human history has been the catalyst for and spoils of more than one war.

Some Web browsing uncovered a document posted by the University of Michigan and one on CNN.com with a variety of interesting water-related factoids:

• The world's population has increased by 1 billion in the last 12 years and could be 7 billion by 2011; 90% of the young live in developing countries in the poorest communities, and 97% of the world's growth over the next 40 years will be in developing countries.
  
• More than 1/3 of the world's population are in water-stressed countries.
  
• In just 15 years, most Asian countries are projected to have severe water shortages; most African countries are currently considered water poor.
  
• On a per capita basis, the average inhabitant in an African country requires 85% less water than a North American and around 80% less than a European.
  
• WHO estimates 5 million people die each year from contaminated water.
  

These sobering facts become more daunting when considering that only 3% of Earth's water is fresh and of that nearly 70% is in ice caps and glaciers, leaving less than 30% in groundwater and 0.3% as surface water. The vast majority of economically accessible fresh water resides underground, most with little or no recharge potential (i.e., nonrenewable). Unlike fossil fuels, there are no viable alternatives to some reserves of nonrenewable fresh water.

An awareness of and interest in solving groundwater problems using geophysics emerged early in the 20th century. The birth of hydrogeophysics as a unique subdiscipline can be traced to the 1980s or early 1990s as it morphed from hydrogeology, geohydrology, and geophysics. Hydrogeophysics gained momentum during the 1990s as practitioners and researchers were driven by the need to map and study contaminant transport and fate in groundwater systems.

By the turn of the century, hydrogeophysics was beginning to flower, with the emergence of focus groups loosely associated with major professional organizations. Hydrogeophysics is defined by Rubin and Hubbard in the introduction to Hydrogeophyiscs (Springer, 2005) as the use of geophysical measurements for mapping subsurface features, estimating properties, and monitoring processes important to hydrologic studies, such as those associated with water resources, contaminant transport, and ecological and climate investigations.

This TLE special section highlights some exciting work in the search for larger and more accessible fresh water supplies and is the first of several publications on hydrogeophysics due in the next year. EAGE's Near Surface Geophysics will have an issue focusing on hydrogeophysics and a 2010 supplement to GEOPHYSICS, specifically targeting electrical methods, is scheduled.

Using nuclear magnetic resonance (NMR) in search of groundwater, initially introduced in Russia, has seen much of the development over the last couple of decades originating in Europe (surface nuclear magnetic resonance or SNMR). It has seen steady development and application (magnetic resonance sounding or MRS) to hold its current place within the hydrogeophysicist's toolbox. In a brief introductory paper, Roy describes MRS and its potential for addressing groundwater problems from a North American perspective. This relatively new technique is also the subject of European researchers Yaramanci and Müller-Petke who provide several case studies that demonstrate MRS's successes and limitations.

Seismic and GPR have been used for decades in hydrogeophysical applications. Parra et al. provide an example of how crosswell seismic can be used in conjunction with formation microimager logs to estimate soft and stiff zones within the inner well region and then correlate those zones to formation log data, which, in their case, demonstrated a lack of continuity between the wells that would have been missed with log data alone. Pugin et al. observed a wave train rich in all seismic modes regardless of source polarization or orientation during 9-C near-surface profiling as they searched for bedrock geometries consistent with localized, high-permeability glacial deposits. Many examples show how GPR has benefited from techniques developed for seismic. Van der Kruk and Jacob show how to identify and invert dispersive GPR guided waves produced when the soil-substrate contact is represented by a strong permittivity contrast.

Resistivity has been a geophysical mainstay in groundwater investigations for a half century. Petersen and Hagrey find new and innovative ways to use resistivity tomography for differentiating different stages of root development by estimating the moisture content of roots and host soils.

As commodities/consumables/resources, it is curious how energy and water are viewed so differently by most in the developed world. Does the fact that water falls from the sky, free to anyone with a bucket, play a role in this perception? A glass of fresh water is the one item that is free at your favorite restaurant. Push the button or turn the handle on any water fountain, common in most public venues, and out comes fresh water at no charge. On the energy side, not much is free. At first glance wind might seem free energy, available to anyone. Unfortunately, it takes more than a bucket to collect and transport wind energy.

Who knows, someday traders on the floor of the New York Stock Exchange might be trading futures in "barrels of sweet Texas crude" in the same pit as "buckets of fresh Kansas potable."

This Article Abstract Full Text (PDF) FREE Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Miller, R.