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The Unintended Consequences of Groundwater Overpumping

Overdrafting of aquifers can endanger not only water supplies but also crucial infrastructure. As communities work to implement new groundwater law requirements, available data can help, writes analyst Samantha Fox.

Written by Samantha Fox Published on Read time Approx. 3 minutes
California sinking central valley
A buckle in the lining of the Delta–Mendota Canal caused by sinking land near Dos Palos, Calif., is evident in this picture taken on Dec. 22, 2015. Years of drought and heavy reliance on pumping of groundwater have made the land sink faster than ever up and down California’s Central Valley, requiring repairs to infrastructure that experts say are costing billions of dollars.AP/Scott Smith

California’s water challenges are clearly overwhelming. Drought, failing infrastructure and questions about management are daunting, let alone all three at once.

During times of drought, farmers and other landowners turn to groundwater to supplement surface water supplies. Until recently, this usage was generally unregulated in California, and individuals often pumped as much as they needed, perhaps unaware of the effect it could have if everyone did the same. Pumping groundwater is a private property right, and landowners, quite reasonably at the time, built farms and business plans on the assumption that the groundwater would always be available.

In 2016, NASA’s GRACE satellite verified that aquifers all over the world are being depleted. Normally, over time, aquifers refill with rainfall, snowmelt and floodwaters, but due to increased use, combined with droughts that dry up surface water, more than half of the U.S.’s aquifers have not been refilling during the past decade. They’re like a bathtub with the plug pulled and the water on, except the plughole is much bigger than normal and the water flow much slower. In short, the tub drains faster than it refills.

One of the most telling cases is in California’s Central Valley. Decades of groundwater pumping have caused the land to sink, a phenomenon known as subsidence. Sometimes, when the land sinks, or compacts, it becomes irreversibly denser, and can’t hold water like it did previously. The result can increase surface flooding and permanently reduce aquifer capacity.

To make matters worse, another problem has cropped up: the impact of subsidence on infrastructure. California has an extensive network of man-made aqueducts, canals and pipelines, many of them located in fertile agricultural valleys where some of the highest groundwater pumping rates occur. Data reveals that some irrigation wells – and high rates of subsidence – are located perilously close to water conveyance infrastructure.

NASA satellite radar maps measured rapidly sinking land in the San Joaquin Valley along the Delta–Mendota Canal, which delivers 3 million acre-feet (3,700 million cubic meters) of water per year to downstream agricultural, municipal, industrial and environmental uses. A large 400 gallons (1,500 liters) per minute irrigation well sits near this area – and as the land subsided 2ft (0.6m), the water in the well dropped 100ft (30m). Are they causally linked?

Radar imagery of subsidence along the Delta–Mendota Canal. (NASA)

Satellite map of surrounding wells; the yellow star indicates a 400 gallons (1,500 liters) per minute irrigation well where the depth of the water dropped 100ft (30m) in the same time period that the land sank 2ft (0.6m). (Water Sage)

Did that irrigation well contribute to the subsidence? If the land is subsiding 2ft in three years, and it is due to groundwater depletion, how is groundwater pumping to be managed so that the Delta–Mendota Canal doesn’t rupture and fail to deliver 3 million acre-feet of water to others who depend on it, not to mention the cost to repair it? The irrigation well owner was operating perfectly legally. What recourse does the well owner have to recover any lost water supply or, due to well-deepening costs, has this well owner’s supply just become more expensive, perhaps due to others’ pumping?

Someone will have to answer these questions soon. Pursuant to the new Sustainable Groundwater Management Act, any area deemed high or medium priority for groundwater management, yet not covered by a Groundwater Sustainability Agency (GSA) by the end of June 2017, will be managed by the state. The area above is located just outside the bounds of a new GSA and is in a high-priority management area. With so much groundwater being pumped in the San Joaquin Valley, there are likely to be more cases like this. Groundwater regulation may not be a pleasant prospect, but it’s got to be better than a busted canal. Pumpers and groundwater management stakeholders must take advantage of available data now to better plan for the future.

The views expressed in this article belong to the author and do not necessarily reflect the editorial policy of Water Deeply.

A version of this story first appeared on Manteca Bulletin.

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