California Colloquium on Water - Leonard Konikow





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Uploaded on May 11, 2009

"Ground Water Depletion: A National Assessment and Global Perspective"
Leonard Konikow, Scientist, U.S. Geological Survey

Abstract: Development of ground-water resources for agricultural, industrial, and municipal purposes greatly expanded during the 20th century, and economic gains from ground-water use have been dramatic. In many places, however, ground-water reserves have been depleted to the extent that well yields have decreased, pumping costs have increased, water quality has deteriorated, aquatic ecosystems have been damaged by reduced ground-water discharge, and land has irreversibly subsided. Some causes and effects of groundwater depletion, however, are neither obvious nor easy to assess. A surprisingly large fraction of ground water pumped from confined aquifers derives from storage losses in adjacent confining layers, but depletion in low-permeability layers is difficult to estimate, rarely monitored, and too often overlooked. A new simplified method for estimating depletion from confining layers was developed, tested, and applied. Results indicate that depletion of storage in confining layers can greatly exceed the depletion from the confined aquifer itself. A nationwide assessment indicates that more than 700 km3 of water was depleted from ground-water systems in the U.S. in the past 100 years. Worldwide, the magnitude of ground-water depletion from storage may already be large enough to constitute a small but measurable contribution to sea-level rise during the 20th century.

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