Header link June 22, 2020

LinkedIn

  • Read more
Header link September 15, 2014

Cart

  • Read more
Header link November 3, 2015

Donate Now

  • Read more
Header link May 15, 2014

Twitter

  • Read more
Header link May 15, 2014

Facebook

  • Read more
Instagram
Header link May 15, 2014

Instagram

  • Read more
Header link May 15, 2014

Contact Us

  • Read more
More options
Water Education Foundation
Home

Water Education Foundation

Everything about California water that matters
  • Water Academy
    • Agriculture
      • Agricultural Conservation
      • Agricultural Drainage
    • Background Information
      • Legislation — California and Federal
      • Regulations — California and Federal
      • Water History
      • Water Rights
    • Bay-Delta
      • Bay Delta
      • Bay Delta Conservation Plan
      • Delta Issues
      • Delta Smelt
      • Sacramento San Joaquin Delta
      • San Francisco Bay
      • Suisun Marsh
    • Dams, Reservoirs and Water Projects
      • California Aqueduct
      • Central Valley Project
      • Folsom Dam
      • Friant Dam
      • Hetch Hetchy
      • Hoover Dam
      • Infrastructure
      • Lake Mead
      • Lake Powell
      • Oroville Dam
      • San Luis Dam
      • Shasta Dam
      • State Water Project
    • Environmental Issues
      • Anadromous Fish Restoration
      • Ecosystem
      • Endangered Species Act
      • Invasive species
      • Lake Tahoe
      • Mono Lake
      • Public Trust Doctrine
      • Salmon
      • San Joaquin River Restoration
      • Watershed
      • Wetlands
    • Leaders and Experts
    • Regions
      • Central Coast
      • Central Valley
      • Mexico
      • Nevada
      • North Coast
      • Pyramid Lake
      • Sacramento Valley
      • Salton Sea
      • San Joaquin Valley
      • Sierra Nevada
      • Southern California
      • Tulare Lake Basin
    • Rivers
      • Carson River
      • Colorado River
      • Klamath River
      • New River
      • North Coast Rivers
      • Russian River
      • Sacramento River
      • Truckee River
      • San Joaquin River
    • Water Issues
      • Climate Change
      • Coronavirus
      • Drought
      • Earthquakes
      • Energy and Water
      • Flood Management
      • Fracking
      • Growth
      • Hydropower
      • Levees
      • Tribal Water Issues
      • Water Conservation
      • Water Equity
    • Water Quality
      • Drinking Water
      • Nitrate contamination
      • Pollution
      • Stormwater
      • Wastewater
      • Water Quality
    • Water Supply and Management
      • Acre Foot
      • Aquifers
      • California Water Plan
      • Conjunctive Use
      • Desalination
      • Grey water
      • Groundwater
      • Integrated Regional Water Management
      • Recreation
      • Surface Water
      • Water Marketing and Banking
      • Water Rates
      • Water Recycling
      • Water Supply
      • Water Transfers
  • Tours & Events
    • Water Tours
      • 2023 Tour Sponsors
    • Events
    • Event Calendar
    • Past Tours & Events
      • Anne J. Schneider Fund Lecture Series
  • Specialized Programs
    • Water Leaders
      • Class Rosters
      • Yearly Class Reports
      • Your Alumni Network
      • Alumni Profiles
    • Project WET
      • Workshops
      • Special Workshops & Events
      • Supplementary Materials
      • California Content Standard Correlations
      • Facilitator's Trainings
      • Foundation School Programs
        • Elementary Programs
        • Secondary Programs
      • Water Kids
      • California Project WET Gazette
      • Gazette Archives
    • Colorado River Project
    • GRA Scholastic Fund Program
  • Maps & Guides
    • Maps & Posters
    • Layperson's Guides
    • Map & Guide Bundles
    • Books
    • Colorado River Materials
    • California Runoff Rundown
    • Other Publications
    • Water Awareness Materials
    • Downloadable Publications
    • Videos and DVDs
      • Video Clips
    • School Age Publications
    • Stickers
    • Free Programs and Publications
  • Newsroom
    • Western Water News
    • Aquafornia
      • About Aquafornia
    • Information Desk
    • Western Water Magazine Archive
      • Full Print Edition
      • Print Edition Excerpts
    • River Report Archive
  • Aquapedia
    • Alphabetical List of Subjects
      • A
      • B
      • C
      • D
      • E
      • F
      • G
      • H
      • I
      • J
      • K
      • L
      • M
      • N
      • O
      • P
      • Q
      • R
      • S
      • T
      • U
      • V
      • W
      • X
      • Y
      • Z
    • Historical Water People
    • Where Does My Water Come From?
      • Northern California
      • Sacramento
      • North Bay
      • South Bay
      • Central Valley
      • Los Angeles
      • Inland Empire
      • San Diego
      • All California Water Sources
    • Timelines
    • Videos
    • Image Gallery
    • Water Directory
      • Federal Agencies
      • State Agencies in California
      • Environmental Organizations
      • Other California Organizations
      • State and Federal Legislative Committees
      • Water Associations and Groups
      • Western States Water Agencies and Districts
    • Online Resources
    • Useful Acronyms
    • About Aquapedia
  • About
    • About Us
      • Board of Directors
      • Staff Biographies
      • Job Openings
    • Announcements
    • Support Our Mission
      • Become a Member
      • Donate in Honor/Memory
      • Donate to Aquapedia or Aquafornia
      • Shop Amazon
      • Planned Giving
    • Contact Us
Aquapedia background February 11, 2014

Overdraft

Overdraft occurs when, over a period of years, more water is pumped from a groundwater basin than is replaced from all sources – such as rainfall, irrigation water, streams fed by mountain runoff and intentional recharge. [See also Hydrologic Cycle.]

While many of its individual aquifers are not overdrafted, California as a whole uses more groundwater than is replaced.

Some 15 million acre-feet of water is pumped each year on average. About 6.5 million acre-feet of water seeps back into the ground as irrigation water is spread onto fields or run through irrigation canals. An additional 7 million acre-feet of water is naturally recharged by rain and runoff percolating into the ground, and still more is intentionally recharged through artificial replenishment projects.

On average, California uses about 2 million acre-feet of groundwater more than is naturally or artificially recharged. Much of the overdrafting has occurred in the agricultural Central and San Joaquin valleys.

As a result, overdrafting aquifers can have long-lasting consequences that are not resolved by a cloudburst or a flash flood.

Groundwater Overdraft Overview

Groundwater extraction for individual years varies considerably.

In dry years, when there is less natural recharge and less surface water available, groundwater pumping typically goes up. In wet years, when more recharge occurs and more surface water is available, less groundwater pumping is needed.

As extensive pumping lowers the water table, the energy costs of lifting water to the surface increases. In extreme cases, the water table can fall below the reach of existing wells, requiring costly extensions or new, deeper wells. But over-pumping can lead to even more serious problems if the excessive extraction takes place over a long period of time – including the lowering or sinking of the land surface, which is called land subsidence, and, in areas along the coast, sea water intrusion.

Another less visible effect of overdraft and chronic declining groundwater levels is that many streams and rivers in the state have become disconnected from the underlying groundwater. This groundwater disconnection can result in the loss of wetlands and riparian habitat and can cause these streams and rivers to go dry periodically.

Meanwhile, in 2009 the U.S. Geological Survey found that about 60 million acre-feet of groundwater has been lost in the San Joaquin Valley since 1961. While the northern and western parts of the valley saw level recovery “overall, the Tulare Basin part of the … valley still is showing dramatic declines in groundwater levels and accompanying increased depletion of groundwater storage.”

Elsewhere, the University of California Center for Hydrologic Modeling at the University of California, Irvine, estimated in 2011 that the groundwater loss in the Central Valley between October 2003 and March 2010 was 16.5 million acre-feet (20.3 cubic kilometers), which is more than half the size of Lake Mead – the nation’s largest reservoir with a 28.5 million acre-feet capacity – the third largest decline in 50 years.

“Continued groundwater depletion at this rate may well be unsustainable, with potentially dire consequences for the economic and food security of the United States.” University of California Center for Hydrologic Modeling.

Overall, persistent overdraft continues to cause problems in California. Groundwater increasingly is tapped to satisfy growing urban needs, to produce about half of the fruits, nuts and vegetables grown in the United States, and to make up for surface water supplies that have been reallocated to restoring rivers and marshes.

  • Print-friendly

Referring Pages

Share this page

  • Share on Facebook
  • Share on Twitter
  • Share on LinkedIn
  • Sent to a friend.
Print-friendly

Related Links

Aquapedia background February 11, 2014
Back
This item appears in:
  • Topic: Groundwater
  • O
Footer pod May 20, 2014

Water Education Foundation

Copyright © 2023 Water Education Foundation. All rights reserved.

The Water Education Foundation is a nonprofit, tax-exempt, 501(c)3 organization, federal tax ID #942419885.

Privacy Policy

Donor Privacy Policy

  • Read more
Footer pod May 20, 2014

Contact Information

2151 River Plaza Drive, Suite 205
Sacramento CA 95833

Telephone (916) 444-6240

Contact Us via email

  • Read more

Quicklinks

Footer quicklink May 20, 2014

Contact Us

  • Read more
Footer quicklink May 20, 2014

Donate Today

  • Read more
Footer quicklink May 20, 2014

Tours

  • Read more
Footer quicklink May 20, 2014

Newsletter Signup

  • Read more
Footer quicklink May 20, 2014

Foundation News

  • Read more
Footer quicklink May 20, 2014

Calendar

  • Read more

Log in

  • Create new account
  • Request new password

Commands

  • Support portal
  • Log in