Groundwater Management
A significant proportion of the global water supply exists as groundwater. Unfortunately, our knowledge of this resource—both its renewable component and its “fossil” reserves—is severely limited both globally and regionally. While most water resource professionals are trained to manage surface water, groundwater is hidden from view and has received relatively little management attention. It is believed, however, that as much as 10% of global annual water consumption may come from depleting groundwater resources. The depletion and pollution of groundwater is identified by many professionals as the single greatest problem of water resources management for the coming century.
Global Dependence on Groundwater
Groundwater is a critical component of supply for cities, industries, and agriculture. Where it exists in accessible quantities, it is often preferred for its reliability in comparison to erratic surface supplies. At least 1.5 billion people worldwide rely on groundwater as their only source of drinking water. Aquifers supplement surface water for irrigation in many countries and are a large reason for the success of the “green revolution” that resulted in remarkable increases in agricultural productivity in the past century. An explosion during the past three decades in the use of wells and pumps for irrigation, domestic, and industrial water supply is resulting in the rapid drawdown of aquifers. As a result, many countries (including China, India, Pakistan, Mexico, and nearly all of the Middle East and North Africa) have enjoyed a temporary “free ride” at the expense of depleting their groundwater resources over the past twenty to thirty years.
Aquifer Depletion
The magnitude of the aquifer depletion problem has only recently become evident. Although comprehensive data do not exist, it is believed that global groundwater over-pumping (i.e., beyond the rate at which groundwater is recharged) totals at least 160 billion cubic meters a year, equal to twice the annual flow of the Nile rivers. For example, the rate at which groundwater is extracted in India is more than twice the rate of recharge, with some water tables now falling by one to three meters per year. As a result, India could lose 25% or more of its current crop production during the next 25 years due to unsustainable aquifer usage rates. Similarly, Mexico is depleting ground water reserves in some agriculturally important regions at rates exceeding 3 meters per year. The implications for global food security are enormous. It is estimated that nearly 10% of the global food supply (160 million tons of grain) is currently based on the unsustainable practice of depleting groundwater.
Aquifer Contamination and Soil Salinization
The contamination of aquifers and salinization of soils compound the problem of managing groundwater resources. Waterlogged soils typically occur in large-scale irrigation projects where surface hydrology is changed substantially. While both surface and groundwater irrigation can be problematic, the problem becomes particularly acute when salts leach from soils and become concentrated through continued recycling of groundwater for irrigation. Salinization can make agricultural lands unproductive and leave groundwater sources and irrigation projects unusable. This is troublesome prospect for countries with low-lying agricultural areas, such as Pakistan. Even more serious from a public health standpoint, contamination of groundwater is also caused by a wide range of pesticides, nutrients, heavy metals, hydrocarbons, and other toxics used in the agricultural, manufacturing, processing, and transportation industries, as well as the by the leaching of such toxics from solid waste dumps. Once polluted, groundwater sources are extremely difficult and expensive to clean up.
Sustainable Groundwater Management
While the problems and causes of aquifer depletion and contamination are clear, immediate solutions are not. Water professionals agree, however, that active aquifer management must be undertaken in the wider context of watershed management. Most solutions involve some combination of increased recharge rate, reduced consumption rate, overall efficiency gains, and reduced or eliminated contaminant sources. For example, reducing the velocity of runoff and providing time for recharge could enhance groundwater supplies significantly and at the same time reduce land-based sources of pollution to receiving waters. Reducing rates of pumping, on the other hand, may involve a close look at linkages with the energy sector and other root causes of over-pumping. Sustainable groundwater management will also require looking at larger management questions, including the development of alternative surface water supplies, reallocation among economic uses of water, and regulatory limits on abstraction. As with other water resources management issues, all elements of active aquifer management must be undertaken through stakeholder participation and whole basin analysis based on projected demand.
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