A number of important ideas, developed during the past 100 years, form the framework of the present understanding of regional ground-water flow. The most important of these ideas are:
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Differences in topographic elevation provide the principal driving force for regional flow.
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Flow through confining layers forms an essential element of regional flow systems.
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Chemical evolution within the flow systems can be used to understand the flow.
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Moving ground water is an efficient transport mechanism for heat within the Earth.
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We trace the evolution of these ideas in the United States and demonstrate their influence on the present-day understanding of flow systems with examples taken primarily from the American literature.