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Groundwater is u nderground water found in the pore spaces and cracks of soil, sand, and rock. The source of all groundwater is precipitation, either through direct percolation into the earth’s surface, or through replenishment from local surface water including lakes, ponds, wetlands or rivers. Sometimes groundwater also flows into surface water through a process called baseflow. The process of groundwater replenishment is termed recharge.
Groundwater is stored in and moves at varying speeds through aquifers. An aquifer is a water-bearing geologic formation that can store and yield usable amounts of water, and consist of permeable layers of soil, sand, gravel or fractured rock such as granite or limestone. They are classified according to type, areal extent, thickness, yield, and direction of groundwater movement. There are two types of aquifers: consolidated rock and unconsolidated rock. Consolidated rock aquifers are composed of limestone, sandstone or other rock. Some, such as granite, are almost impervious and yield very little water, while others, such as limestone, are very porous and can yield vast amounts of water. Unconsolidated rock aquifers are composed of granular materials such as sand and gravel and typically yield larger amounts of water.
Aquifers are also confined or unconfined. Unconfined aquifers are typically located near the land surface, are composed of permeable materials such as sand or gravel, and recharge quickly, making them susceptible to contamination. The area of the aquifer that is filled with water is termed the saturation (or saturated) zone; the top of the saturation zone in an unconfined aquifer is termed the water table or phreatic surface, where water pressure equals atmospheric pressure. The area between the saturation zone and the land surface is the vadose zone.
Confined or artesian aquifers are typically located at greater depths and below impermeable layers such as rock or clay. They are typified by little or no recharge. For this reason, they often contain what is termed fossil or geologic water, and are thus susceptible to mining. Groundwater mining occurs either when groundwater extraction exceeds recharge (as in unconfined aquifers) or when groundwater will not be recharged naturally as in most confined aquifers. Artificial recharge is also possible either through the direct injection of water into the subsurface as in California or through directed rainwater recharge as is increasingly common in northern India.
Contrary to popular myth, groundwater does not flow in rivers or channels beneath the earth’s surface. The one exception is with Karst topography. Karst (an area of Slovenia) topography is where the solution of limestone, dolomite, gypsum, or marble, creates very erodable areas on the land surface or underground. It is possible for water to flow through the underground caverns created through this process. Karst is found in the U.S. states of Florida, Texas, and Kentucky, and in China, Slovenia, and Turkey.
Groundwater flows through aquifers toward lower elevations through the force of gravity. In confined aquifers, however, groundwater can flow up gradients, causing artesian conditions, where groundwater flows to the surface due to pressure created through the confined character of the aquifer. This occurs along the foothills of the Rocky Mountains in the United States, but is also common in other areas.
The largest aquifer in the United States is the Ogallala Aquifer (also called the High Plains Aquifer). It is an unconfined aquifer located in the states of South Dakota, Wyoming, Nebraska, Kansas, Colorado, Oklahoma, Texas, and New Mexico. The thickness of this aquifer ranges from 1 (0.3 meters) to 1300 feet (396 meters) and covers an area of 175,000 square miles (453,250 square kilometers). The Ogallala is used mostly for irrigation, especially in the Southern High Plains, but also supplies water to many cities. It irrigates 20 percent of total irrigated area in the United States, or 11,000 square miles (28,490 square kilometers), with a yearly discharge of 12 billion cubic meters of water. It has been heavily mined in Texas, with smaller declines occurring in other states. The future viability of the Ogallala is threatened due to overdraft.
In many parts of the world, including parts of the United States, Europe, Australia, Southwest Asia (i.e., the Middle East), Mexico, China, and India, groundwater is overexploited, with extraction surpassing recharge. This is of serious concern as groundwater is highly relied upon throughout the world. For example, it provides 51 percent of all drinking water in the United States, and in India supplies 70 percent of irrigation water and 80 percent of its domestic water. The largest user of groundwater in the world is irrigation. The advantages of groundwater over surface water for drinking and irrigation purposes are many: it is reliable in dry seasons and during droughts; it is cheaper to develop, since when unpolluted it requires less treatment than surface water and can be tapped by individuals, decentralizing costs to individuals; and it can be tapped when and where needed, such as at the household level, reducing expansion (of capacity) and conveyance costs.
There are several concerns, however, with this massive reliance on groundwater. The first is overexploitation. Second, groundwater is very susceptible to contamination. Contamination is both humaninduced (anthropogenic) and due to naturally occurring minerals. Anthropogenic causes of groundwater contamination include gasoline, oil, road salts, storage tanks, septic systems, hazardous waste sites, landfills, and industrial chemicals. One gallon of gasoline (3.8 liters) can contaminate one million gallons (3.8 million liters) of groundwater, making it unsuitable for drinking purposes. Furthermore, it is estimated that over 10 million underground storage tanks and over 20,000 abandoned hazardous waste sites exist in the United States. Naturally occurring sources of contamination include arsenic and fluoride. Arsenic contamination is a major source of groundwater contamination in the Ganges Plain of Bangladesh and northern India. As groundwater is withdrawn, naturally occurring mineral concentrations can increase, making groundwater unfit for human consumption or for irrigation. Third, saltwater intrusion may occur in coastal areas as groundwater withdrawal alters normal groundwater flow, inducing seawater to flow into nonsaline aquifers. Fourth, excessive groundwater withdrawal can cause the land surface to subside as it has in Mexico City, and in New Orleans, Louisiana, and Las Vegas, Nevada. Fifth, in many areas excessive groundwater withdrawal is substantially reducing baseflow to wetland and riparian areas, adversely impacting riverine and riparian species of flora and fauna. This has sparked fierce debate in the Platte River and the Ogallala Aquifer system in Nebraska, and also in the Edward’s Aquifer and San Antonio River system in Texas. And finally, these issues all lead to the matter of groundwater governance.
Governance of Groundwater
The greatest challenge for the 21st century facing groundwater is one of governance. When the first laws were created for water use, surface and groundwater were thought to be distinct. Historically, therefore, laws governing the use of surface and groundwater have treated these two separately, even though they are connected. This, in part, has led to a confusing set of legal institutions governing groundwater. Further complicating water law is the lack of legal standing for nonhuman uses, such as in-stream flow needs of fish and other flora and fauna.
Multiple formal and informal institutional arrangements have evolved for the management of groundwater. In the United States, groundwater regulation is the domain of individual states. Regulatory and rights structures vary by state, with much of groundwater management resting with local institutions as in Nebraska and Texas. There are four categories of groundwater rights in the United States. States east of the 100th meridian follow the Doctrine of Riparian Rights, while those west of the 100th follow the Colorado Doctrine (strict Prior Appropriation) as practiced in New Mexico; the California Doctrine (Correlative Rights Principle – a combination of riparian rights and prior appropriation) as practiced in California and Nebraska; or Absolute Ownership, as practiced in Texas.
The Colorado Doctrine of strict prior appropriation allows a landowner to use water based on historical precedent: “first in time, first in right.” The amount of water provided with a water right is based on the amount of water historically diverted and put to beneficial use: “use it or lose it.”
The California Doctrine applies the concept of “reasonable and beneficial use.” The appropriative right/use must be deemed economically beneficial; otherwise, a riparian user has the right to co-opt its use. For example, a rancher using water to irrigate alfalfa could lose their right to water if an industry could produce more capital with it. This differs from strict prior appropriation in that it distinguishes by use, where as strict prior appropriation does not.
Groundwater rights in Texas are based on absolute ownership and the “right of capture.” Under absolute ownership, the “landowner owns everything on his or her property from the land surface, up to the heavens, and down to the center of the Earth.” In theory, there are no limitations on pumping for the current or future based on current or past use, and it is legal to sell groundwater. In Texas, local institutions have formed for the management of groundwater. The High Plains Water Conservation District Number 1 (HPUWCD) is one such local organization. Comparisons of the New Mexico state centered model with the Texas self-organized model of groundwater management indicate that statemanaged groundwater usage is not superior to self-organized local management of the HPUWCD.
The most recent iteration of the debate surrounding the governance of groundwater boils down to essentially whether it is a public or a private good. Historically, water has been thought of as a public good, held in the public trust, for the use of all people for consumption, sanitation, aesthetic values, and environmental protection. Viewed as a private good, water can be developed, used, traded, and sold for economic productivity and financial gain. It is this latter view that is gaining currency around the world.
Under this second view, proponents follow the logic of Garret Harding that groundwater is an open access resource and is subject to the “Tragedy of the Commons.” They argue that private property rights over groundwater should be established yielding transferable or tradable rights that under the laws of supply and demand will inevitably move water toward the highest value uses, while preventing the problem of open access. But to think of groundwater or any resource as open access is to ignore that they are actually common pool resources and are subject to localized rules of use and institutions, which govern their use, distribution, and protection. Furthermore, it is problematic because uses such as irrigation will always have lower value added than industrial production, shifting water away from important primary commodity production. This would have drastic effects in developing countries such as India, where peasant producers rely on small plots of land and groundwater irrigation, the rights to which would probably be transferred to a higher economic use. Similarly, in a market-based system there is little incentive to protect stream flows or others’ property through reduced groundwater pumping. Groundwater is both a private and public resource. The solution is not, therefore, in either extreme but somewhere in the middle, taking into account local context and the local historical development of groundwater management expertise and institutions.
- Brooks and J. Emel, The Llano Estacado of the U.S Southern High Plains: Environmental Transformation and the Prospect for Sustainability (United Nations University Press, 2000);
- Thomas Cech, Principles of Water Resources: History, Development, Management, and Policy (John Wiley & Sons, 2005);
- Rosegrant, X. Cai, et al., Global Water Outlook to 2025: Averting an Impending Crisis. (United Nations, 2002).