@USGS Report: 'Groundwater Depletion in the United States (1900-2008)' Plus More!

Great report from friend and hydrogeologist extraordinaire Leonard (Lenny) Konikow, another Long Island kid, but one who made real good - Groundwater Depletion in the United States (1900-2008).

Abstract

A natural consequence of groundwater withdrawals is the removal of water from subsurface storage, but the overall rates and magnitude of groundwater depletion in the United States are not well characterized. This study evaluates long-term cumulative depletion volumes in 40 separate aquifers or areas and one land use category in the United States, bringing together information from the literature and from new analyses. Depletion is directly calculated using calibrated groundwater models, analytical approaches, or volumetric budget analyses for multiple aquifer systems. Estimated groundwater depletion in the United States during 1900–2008 totals approximately 1,000 cubic kilometers (km³). Furthermore, the rate of groundwater depletion has increased markedly since about 1950, with maximum rates occurring during the most recent period (2000–2008) when the depletion rate averaged almost 25 km³ per year (compared to 9.2 km³ per year averaged over the 1900–2008 timeframe).

Note that 1 km³ equals about 810,000 acre-feet, so over the entore timeframe we are talking about a depletion of about 810 million acre-feet! And since 2000 we're depleting our groundwater at an average annual amount of over 20 million acre-feet.

Brett Walton wrote about this report (and included Lenny's comments) in his excellent Circle of Blue article: 

Download Circleofblue.org-US_Groundwater_Losses_Between_19002008_Enough_To_Fill_Lake_Erie_Twice

Walton pesents this map, from the report, but with additional information below:

The United States has lost enough groundwater to fill Lake Erie twice. The biggest declines occurred in the Southern Great Plains, the Mississippi River Delta, and the Central Valley of California. Two aquifer systems in the Pacific Northwest show net increases since 1900, but those trends have reversed in the last few decades. 

And he concludes with several results of excessive pumping - two that have been known for quite some time, another one not so well-known:

A number of effects follow extensive groundwater pumping. For one, it can siphon water away from rivers. In January, for instance, Texas filed a lawsuit in the U.S. Supreme Court alleging that groundwater withdrawals in New Mexico were cutting into its share of the water from the Rio Grande.

Another problem is that if too much pumping happens, the land can drop along with the water table, a process called subsidence. Stretches of California’s Central Valley have dropped several meters in elevation since widespread pumping began there in the 1920s.

The least well known effect is on sea levels. According to Konikow’s calculations, roughly 1.3 percent of global sea level rise in the 20th century and 2.3 percent of the rise from 2000 to 2008, when pumping accelerated, can be attributed to groundwater depletion in the United States — and that is just the contribution from one country. Add the rest of the world, and groundwater withdrawals are responsible for 6 percent of the observed rise in the oceans, Konikow reckons. (Other estimates have put the figure several times higher, but Konikow told Circle of Blue that those studies overstate the effect.)

Konikow acknowledges that his estimates for U.S. groundwater depletion are not perfect. Scientists cannot measure the volume of an aquifer directly. Instead, they extrapolate from various measurements, based on well depths and the porosity of soils. Konikow told Circle of Blue that the margin of error for the study is approximately 20 percent above and below the 1-trillion-cubic-meter (264-trillion-gallon) estimate of depletion.

[Note: here is the paper by Lenny about the contributions of groundwater depletion to sea-level rise: Download Konikow_2011b]

Not real good news. Time to get more serious about groundwater management.

“In many of these systems, we’re removing water faster than it is being replenished. That is not sustainable in the long run.” - Leonard Konikow, from the Circle of Blue article

Comments

[geohydro]

Ha. I had to laugh when I read that Texas was suing New Mexico. Texas state policy allows, hell I'd say, encourages, mining of groundwater. It is possible that it is primarily Texas-based groundwater withdrawals that are causing stream depletion.